106 - Chemistry of smoke - Nitrogen, retardants and cancirogens with David Purser

Fire and Smoke Hazards

Speaker 1 0:00

Hello everybody , welcome to the fire science show .

Speaker 1 0:03

Today we're here with a final episode with Professor David Purser on toxicity and toxicological hazards related to fire , smoke and fires in general , and this serves as a summary to the previous content .

Speaker 1 0:17

So we've learned a lot about how chemicals are produced in fires . We've learned a lot how we measure them . Today we're gonna learn a bit more about the role of nitrogen . We're gonna learn a bit more about how fire retardants can change the fire atmosphere and the toxicological hazards related to fires . We're gonna learn about smoke , not only inside the building but also outside the building , and the dangers related to , let's say , wildfire smoke or large chemical fires that can affect whole cities . And in the end , we're gonna also learn about some more long lasting hazards related to consurgents and properties of smoke that are related to cancerous hazards , and what parts of our profession are particularly exposed to such hazards . So another great episode with David , another episode jam packed with chemistry , perhaps again a little difficult one to digest , but definitely full of great knowledge , full of great examples , full of interesting stories from the life of an amazing , amazing scientist who is one of the most impactful figures in the field of toxicology and fires , undoubtedly this year's recipient of Howard Emond's plenary lecture at the .

Speaker 1 1:43

FSS The biggest honor that a fire scientist can have . So I'm very , very happy for the full time to have David Pusser in the fire science show . Let's spin the intro and jump into the episode . Welcome to the fire science show . My name is Vojty Wigzynski and I will be your host , As usual . I would like to say thanks to the sponsor of this podcast , ofr Consultants . So this podcast is brought to you in collaboration with OFR Consultants , a multi award winning independent consultancy dedicated to addressing fire safety challenges .

Speaker 1 2:31

Ofr is the UK's leading fire risk consultancy . Its globally established team has developed a reputation for preeminent fire engineering expertise , with colleagues working across the world to help protect people , property and planet . In the UK that includes the redevelopment of the Printworks building in Canada Water , one of the tallest residential buildings in Birmingham , as well as historical structures like the National Gallery , national History Museum and National Portrait Gallery in London . Many the work ranges from Antarctic to the Atacama Desert in Chile , to a number of projects in Africa 2023, . Ofr is growing its team and it's keen to hear from industry professionals who want to collaborate on the fire safety futures . This year . Get in touch at OFRConsultantscom . So just to make sure you're on the same page last episode . We've discussed how equivalency factors influence the different yields of products , how we measured that , and we've ended the discussion coming into the role of nitrogen in fires . So let's continue on nitrogen .

Speaker 2 3:32

So just to go a little bit further on the nitrogen thing , as I was saying , when you burn carbon in a fire , when it's well ventilated , you get lots of carbon dioxide , which is a fully oxidized version of carbon , and as you become under ventilated , the carbon dioxide yield starts to fall off in a predictable way . So when you measure carbon monoxide , there's none under well ventilated conditions and that increases as you get under ventilated . Well , exactly the same sort of thing happens with nitrogen . So when you've got organic nitrogen in your fuel , if you burn it under well ventilated conditions , you get oxides of nitrogen produced NO and NO2 , nox , which you know is under well ventilated conditions , which we know is a big problem in automobile engines .

Speaker 1 4:17

I feel a lot with that in road tunnels where we need to calculate NOx production from diesel engines and it's difficult to manage .

Speaker 2 4:26

yes , Now in engines . Probably most of it's coming from nitrogen in the air . In this case , I'm talking mainly about nitrogen products from organic nitrogen in the fuel that we're burning , which is .

Speaker 1 4:39

Are there many more organic materials , plastics that would have nitrogen in the structure , besides polyurethane ?

Speaker 2 4:46

Yeah , there's a whole load of them and to some extent they're more common in our environment than they were years ago . So of course you've got a classic one is polyamide nylon , which is because it's got a lot of cyanide when it's burned . I've done a lot of work with that .

Speaker 2 5:00

And then you've got , obviously , the polyurethane . So the stuff you've got in your furniture which is flexible polyurethane phones , they have quite a bit of nitrogen in , and there's another material called polyacrylonitrile , which is used to make various fabrics for clothing and for covering furniture , which is high in nitrogen . The use is quite a bit of cyanide when it's burned . And then you've got the rigid foam materials that are used in construction , which also have a quite a lot So there's quite a few nitrogen-fueling fuels .

Speaker 1 5:31

We work with this material actually a lot and it's increasing . Poly isosanerate , pir they are used a lot as thermal insulation and elements of facades .

Speaker 2 5:42

I've done a lot of work with PIR .

Speaker 1 5:43

that gives off quite a bit of cyanide , So actually the plastics that involve nitrogen in the structure would be commonly found in buildings , not only in your upholstery , where you would find PU , but also within the structure of the building , even and in form of those , maybe foams that are used to insulate it or some other . But it's okay . I just wanted to have a quick overview How relevant the nitrogen discussion is .

Speaker 2 6:09

You may remember , the last time we spoke I was saying that getting some kind of feel for the nitrogen content of your burning fuel is important and can have quite a big consequence , so that if you think of most cellulosic materials , which only have one or 2% nitrogen in , then any toxicity is going to be dominated by the carbon content because the nitrogen content is so low to start with . When you get something like a single armchair burning which is an insulation panel that has a high nitrogen content , say 10% or so then you need to consider carefully how much cyanide you might get if it burns in your particular scenario . But if you look at the terrible fuel load in a building then , as I was saying last time , it tends to be very much dominated by the cellulosic components . If you think of your office I look around me now it's full of books and wouldn't show any to you .

Speaker 1 7:01

I have a pulsed wall , so mine is full of good old nitrogen .

Speaker 2 7:04

Oh , well , there you are , you'd better get out quick . Yeah , sorry , i mean , that's the sort of thing that happened at the station nightclub , for example , which was a very , very rapid , like urethane burning fire .

Speaker 1 7:14

Okay , i broke your train of thought and it was intriguing . So you said that in well-oxidated conditions the main products would be NO NOx .

Speaker 2 7:23

Actually the main product still is N2 , which is harmless . There is a significant , or can be a significant , yield of NO or NOx And so we worry about that because it's an irritant , a long irritant . But once you get to , as the equipment strategy goes above one , you find all that NOx nearly all disappears because you're now under ventilated conditions . So just CO2 disappears , so NO disappears with me , and what we start to see is the non-oxygen containing components coming up , so or less oxygen . so we start to get CO coming up , we start to get HCN coming up right as a product . So they're kind of mirror images the CO2 and NOx drops away and the CO and the HCN comes up in terms of yield as we get into more under ventilated combustion condition .

Speaker 2 8:13

That was the point I was making . So basically , these are the sort of phenomena that are going on . As I said , what we set out to do as we developed this over the years was to come up with an apparatus where we could measure these things for different individual fuel materials , get them to burn with a flame . so we're really interested in flaming combustion And one of the requirements of the test , if you're doing it properly , is that you observe to make sure it's burning with a flame throughout the run . so it must be burning with a flame . and then you know the defined oxygen fuel ratio and you know the temperature , because you've got the furnace temperature measured and we calibrate all that . So then you can then correlate or define your yields of your products against those criteria . Use it burning with a flame , what's the sort of temperature regime that we're operating in and what is the fuel air ratio , and you then measure the yields of all the products of interest that you're interested in doing So , and then you can produce plots of those as a function of equivalent ratio for a known temperature regime , and I've said I'll try to fit algebraic expressions to these curves

Speaker 2 9:23

as altitude , and then you'll find them in the handbook , both minor and arches . What we get is a sort of sigmoid curve as a function of equivalent ratio of yield . So I fitted viable expressions to my curves , try and capture that sigmoid sort of shape . But what was very , very important to me was these yields that I'm getting under these conditions I've defined in my apparatus . Do you get the same yields under the same defined conditions in arches apparatus ? And , more importantly , do you get the same result in something like an ISO room test or a compartment fire test ? Now , of course , the problem is that the data that we've got for multiple repeat tests under ranges of equivalent ratios in full scale compartment fire tests is quite small because they're complicated and difficult to do . So it's a limited data set , but we do have some . I've done quite a few . And then there's the work . You'll find some in the handbook bio-less work pits and various people like that . So we do have a bit of a database of known fuels decomposed under a range of combustion conditions in compartment fires , for which we can measure the equivalent ratio of conditions produced them , and we can measure the yields of CO with time , et cetera , in these tests . And so what I've done was it's the last paper I published on this was to compare the yields I was getting in the tube furnace with the yields measured as a function of these parameters in compartment fire tests . And I feel we're getting pretty good agreement , and certainly quite good agreement with Archie's tests . So this makes me feel confident . We're measuring phenomena that are not apparatus dependent , not test dependent . They're physics dependent or chemistry dependent , and we're defining what we will get . I'm saying , if you set up these conditions , you should observe something pretty close to what I'm measuring , whatever apparatus you use , providing that you're careful to define your conditions . And this is one of the problems I've found with the tube furnace is that I feel I nurtured this wonderful baby in my laboratory And now it's grown up to be a rebellious teenager .

Speaker 2 11:44

People are using it around the world in all sorts of ways that perhaps they're not being as careful as they should be about accurately measuring their parameters . I'm getting some people again . It's an odd result , but what we found is that you have to be very , very , very careful , particularly to measure accurately your air supply . It's quite easy to measure the mass presentation rate of the fuel . You just set up an injection device at a constant rate , but people seem to not be able to accurately measure their air flows , and so if you get your airflow wrong , you get your actual fuel-air ratio , which can be very different from your nominal fuel-air ratio . Then you get funny results , and so , to try and deal with that , in the more recent version of the standards of this , we've told people to do test runs with PMMA and known fuels like that under certain conditions , and they have to make sure they get certain results to demonstrate that they've correctly set up the apparatus before they start with unknown materials . When I'm doing that , we're finding things improved .

Speaker 1 12:49

So basically , you're making them make sure they are in the same apparatus-independent regime as you were with the others .

Speaker 2 12:56

Yeah , exactly , you've got to calibrate things very accurately , because the problem is , this apparatus is something you more have to build yourself . You can't just bite off the shelf like a concoil image . So while I'm you know , something like concoil image there is .

Speaker 1 13:08

I'm pretty sure there's a company who can sell you one .

Speaker 2 13:11

Well , there are one or two . I mean the concoil image , for example , is very widely used in the bugs that have been ironed out on its physical use of the apparatus , So that's not really quite the case , we are proud owners of one person's furnace in our laboratory , and we like it . Well , yeah , so I'm pleased with that .

Speaker 1 13:31

I cannot guarantee we were using it correctly , though , after all of this , but please , please , contact me if you have any problems too .

Speaker 2 13:39

So I think we're getting somewhere . You know , I think we now have a handle on a better understanding of the main criteria that determine the yields of things under fire conditions , And maybe we do find some differences for a given equivalence ratio . If you operate at 900 degrees centigrade , you slightly get different yields from if you operate at 600 degrees centigrade with a flame on both casations And that's understandable in terms of chemical dynamics , which is a complicated subject .

Speaker 1 14:06

That's what I just wanted to ask you about maybe , maybe you can help me . I have two . now , as I understand how the yields and properties of the products are measured , i wonder . I want two things . One is to what extent is my upper layer in a compartment fire ? To what extent can the furnace really well capture these conditions ? Is it really the same thing ? And the second thing is to what extent these things would be dynamic , like to what extent the products directly above my plume would be different from smoke , let's say , 20 meters away , like how quick ? Yeah , all very excellent questions .

Speaker 2 14:53

Yes .

Speaker 1 14:55

So let's start with the compartment fire , and to what extent .

Speaker 2 14:59

I get to think of a compartment fire . So one distinction I want to make is between other apparatus , a bit like the cone parameter or like arches apparatus , where you have a static fuel and a dynamic airflow . So you just have a fuel is in some of a sort of circular plate , isn't it in most of these apparatus , and then you irradiate it from above with the cone parameter or from the side in arches apparatus , and you heat that up and it starts to decompose and burn with the flame And you measure the mass loss rate of your fuel And certainly in arches apparatus you can measure the air combustion air .

Speaker 1 15:34

One of the issues with this approach , or what features this approach , is that if you're burning something like polypropylene .

Speaker 2 15:41

That will then melt into a hydrocarbon fuel and will then paralyze off at a certain rate in the combustion zone , and the composition of the aerosolized fuel pyrolyzate before it's combusted will be fairly constant until it's all gone . It doesn't change in composition during the test . If you take something like a lump of wood , then it's very different , because the work starts off as being wood , with all the volatiles in the wood , which then starts to paralyze and burn with the flame , and then gradually the carbon content of what's left increases until you get a chore left in the end , and so the composition of the burning fuel and the pyrolyzate that's coming off that fuel changes throughout the curation of the test , and that's OK . But you have to be aware that that's what's going on .

Combustion Analysis in Tube Furnaces

Speaker 2 16:28

When we're doing CFD analysis or when we're thinking of combustion in the upper layer or in the combustion zone of a fire , we're really thinking about the composition of the gaseous components , not the solid left behind .

Speaker 2 16:44

So in this case we've got a changing fuel . I mean so if you actually think of a lump of charcoal , the only thing you've got to get off that is carbon which you heat it up , whereas if it was wood there's all sorts of stuff comes off wood in the early stage , whereas in the tube furnace we're burning fresh material all the time . So what's happening in the tube furnace is more , i would say , analogous to what's happening in a spreading fire . If I have a wooden table and somebody leaves a candle at one end and sets fire to one end of the table , then the flame zone moves along the table to spreads and expanding circle to involve more and more fresh material all the time . Or if I'm set fire to a wall lining , the flame goes up the wall and induces a new material . So real fires or spreading fires compartment fires are spreading fires And so what we'll do in a tube ? it sort of replicates the spreading fire type scenario rather than this lump .

Speaker 1 17:46

So the stage you have in fuel and it decomposes the early stages of the composition as it ignites , loses the first volatiles .

Speaker 2 17:54

That's right . So we have a bit of both in ours , but anything about what's happening above your burning fuel . So when it's above your burning fuel you have what we call the plume fire plume coming off above the fuel which is in training air And that's where we get primary combustion zone , where the flames are And that's where we have our fuel-air ratio equivalence ratio in our burning flaming plume And there's a parameter called the plume equivalence ratio that people mentioned . I think what we're doing more or less replicates that plume equivalence ratio situation . Then there is the product of combustion , then go into the upper layer And , as I say , most of the work I've done large scale , far as I'm looking at are under ventilated fires . So we have quite a deep upper layer and the flames are penetrating into the under-vitiated upper layer because you've got less oxygen up there , you're getting quite under ventilated conditions in your upper layer And as that flows away from the combustion zone , the temperature drops And once the temperature drops the chemistry slows right down . So essentially the upper layer is very low in oxygen . Usually most of the oxygen is gone And so if you've got a layer a meter deep , it's flowing away from your flame zone horizontally towards and , say , a doorway , then most of the entrainment is happening close to the burning fuel .

Speaker 2 19:23

There are some , but limited , entrainment into the upper layer , remote .

Speaker 2 19:27

As it flows away , and as the temperature drops the chemistry starts to freeze And so the relative composition of the different , say , carbon dioxide to carbon monoxide ratio becomes constant , becomes thick as the plume cools down and moves away from the combustion zone . Well , you can get secondary combustion , as if you for some reason introduced fresh air into that plume while it's still sort of 6 , 7 , 900 degrees centigrade . Then of course you'll get further combustion . And you may be aware of this famous paper that I think Pitt and Co did , where they looked at the global equivalence ratio particularly and they introduced , tried introducing air into a vitiated hot upper plume when they got further combustion in there . Of course that can happen , and in tube floneness we have the potential to examine this phenomenon by putting a lot of atmosphere through the tube and heating it to different temperatures . If you take that fuel-rich atmosphere and put it through another tube and then heat it up or cool it down , you can investigate those conditions , but you'd have to set them up as a separate entity .

Speaker 1 20:34

My God , if any students are listening , just take down notes , because these are like they're a brilliant , brilliant piece . I mean what I It used to be done .

Speaker 2 20:43

I'm a little bit frustrated because to me a tube furnace another other type variants of it was such a wonderful platform to investigate all these phenomena . There's so many tunes you could play on it by very having maybe two tubes in series with different heaters around them .

Speaker 2 21:00

I love it Or by putting various gases in , and one of the things , for example , with NookTak , is if you What an horrific question you should ask me is if I have one fuel burning say I have wood burning when I get a certain condition and a certain CO2-CO ratio , and then next to it I'll have a lump of PVC burning and the two flumes mixed , will the yield of CO from the wood be affected by the yield of hydrogen chloride from the PVC ? You ?

Speaker 1 21:29

see what I'm going to get ?

Speaker 2 21:30

And I'd say the answer is if you burn them as two completely separate fuel packages and only mix the plume where the temperatures drop down to sort of below 400 centigrade , then they're just be additive . Parallel tubes Yeah , just parallel sources of , yeah , sources of material . They only compile in flour anywhere . So you could treat each fuel as independently acting and just putting smoke up into the , up a layer , right . But if you had your PVC intimately connected with the wood so that both are burning together , then you'd expect to see a big increase in the CO yield from the wood component because the chlorine atoms in this flume , in this flame plume , are going to reduce the efficiency of combustion of the carbon from the wood . Now , i know this is theoretical , but it has actually been done . So I think Anna did a bit .

Speaker 2 22:26

I've done a little bit in the two films , but there was a very nice experiment , and years ago in an ISO room corridor rig And I like room corridor rigs rather than a nice civil ISO room So this is Many years ago we used to have this at BRE .

Speaker 2 22:39

So we had an ISO room with a doorway and the doorway open to a corridor which goes right angles across from the loom And then the end of the corridor , which might be 20 meters long to 15 meters long , you'd have your hood , and so this is a very interesting piece of kit because you can generate your fire in the ISO room and then you can have the plume and it relates back to your previous question .

Speaker 2 23:05

You have the plume flowing down , the Hot plume flowing down as a ceiling layer down the corridor , then coming out of the Into the hood at the end where you can measure the product . But in these experiments , which were done many years ago , we took Well , i wasn't involved in them personally , but Peter Fardell and his colleagues took samples of smoke from the plume as it moved down the corridor . So when it starts to come down the room , it's very hot . Well , as it moved down the corridor and there's some entrainment from the air below , well , it cools down And they did in fact find some . When they're close to the very hot area , they did find getting some oxidation of the carbon monoxide to CO2 as it went down the corridor and there was some entrainment , the monoxide did decrease .

Speaker 1 23:50

The concentration of monoxide was Yeah , something like that .

Speaker 2 23:53

But also one of the Tesla get was they built . These are 100 kilogram cribs , wood cribs , you know what they are . So you built 100 kilogram crib and they were burned to completion in these tests And one of the tests they replaced the upper quarter of the rig with PVC . So the energy is mainly coming from the burning wood crib , but the top half of the crib is PVC And they unfortunately didn't have the equipment to measure hydrogen chloride . But what they did find was a big increase in the CO yield And what's happening was that the PVC was , i think , affecting the combustion efficiency of the wood . So there are all sorts of interesting games one could play experimentally and PhD-wise on looking at all these phenomena . They're very interesting .

Speaker 1 24:38

Everyone's familiar with catalysis for combustion engines , where you put a piece of platinum to make the exhaust less toxic because you complete the combustion of them . So I guess the chloride is doing something opposite And it slows down the reactions or affects the capability of the interactions to cure . So this is brilliant . And another level of complexity I have not even thought about , like how different radicals present in the atmosphere where the combustion is happening will influence the reactions . That happened there Brilliant .

Speaker 2 25:14

There's particular the halogens that , because this is the principle of a lot of phyretolidin hadithes , that's why they put in the first place .

Speaker 1 25:20

Very interesting .

Speaker 2 25:21

With the gold side of the mist that they make it less likely that you're going to have a phoric nitrogen .

Speaker 1 25:26

It seems to me to say , mechanism may be even actually .

Speaker 2 25:30

It is . The good thing is that if you think of all the possible ignition sources that might attack your material , the probability that you get ignition in the first place is reduced if you've got some phyretolidin syndrome And hopefully if you do get ignition you will then get a slow growing phyton And there is some evidence for that . But the downside is that if you do get a large phy redeveloping , the yields of toxic products are likely to be higher of a normal toxic product like slow , and of course you're introducing fresh toxic products from the retardants themselves . So there's a trade-off there And of course there's a whole , as we were discussing , there's a whole another field of consideration there about where we should be going with phyretolidins , flame retardants and a whole new sort of field of environmentally friendly flame retardants that can hopefully achieve some improvement in performance without producing a lot of or giving us a lot of toxic products , both from their actual use as manufacturing , use in the environment and when they're involved in fires .

Speaker 1 26:35

David , i would like to try the previous interview to this one . In the previous interview we opened it with view on the fires in the 40s 50s that they were less harmful to the participants , and then observations that towards 70s , 80s , with the change of materials and stuff , the toxicity has increased . Now , based on what we've said today , it seems that the fires became bigger and because of them being bigger , they consume oxygen better , meaning they get higher equivalence ratios , less efficient combustions and the products increase exponentially with that change . Do you find this the reason of this increased toxicity ? The fires grown bigger , they're faster and equivalence ratios are different .

Speaker 2 27:25

This is where some complexity does come in .

Fire Retardants and Toxic Products

Speaker 2 27:28

We did a series of experiments in these room corridor rigs and also in a house .

Speaker 2 27:34

We had a typical suburban house where we did a series of armchair-type fires in the lounge large of the house , with the lounge doorway open or one bedroom upstairs open , so they had a fire room and an extension beyond it , but they otherwise it was enclosed , so these were enclosed fires .

Speaker 2 27:52

We did find a slightly anomalous result in the real world that you wouldn't find if you didn't go and look for it in the full scale . If you didn't replicate the full scale scenario properly , you would not necessarily observe this , and it was something along the lines of the yield for gramma fuel burned of the more retardant treated materials was somewhat higher . So you might get more CO grams per gram of material burned because of these inefficiencies that you're introducing . But when we ignite the fire in an enclosed space you get a layer descending from the ceiling , an officiated layer descending from the ceiling . As more and more of the flame plume from the fuel gets into this upper layer , you start to suppress the fire Because it's oxygen depleted when the oxygen concentration in this upper layer gets down to a certain level , the fire goes out .

Speaker 2 28:53

Because by the time the layer is descended by a metre or two , nearly all the flame of your burning chair is burning in more or less in the upper layer . And once that upper layer oxygen concentration gets down to about 15% oxygen , the fire goes out . 10% to 15% oxygen . What we found was , with the armchairs that were not treated with retardants , the fire would keep burning longer in a layer oxygen concentration in the upper layer in the environment And because it burned for longer before it self-extinguished , it would produce more toxic products . And not only that because it was burning in a more under-ventilated equivalence ratio conditions , the yield of CO went up and cyanide went up . See what I'm getting at . So because it was well as the flame-retardant treated material , the whole fire went out at a lesser level of oxygen depletion .

Speaker 1 29:49

So at higher oxygen concentration .

Speaker 2 29:51

Yeah , so sorry I won't forget to say . Remember I said this scenario . We had the fire burnt in the room when the layer got below the soffit of the doorway . The flame flowed out through the doorway into the hallway and upstairs in the house right , and then that layer filled down outside and one of the things we measured was the oxygen concentration of the air in the doorway near ground level . So this is the air coming into the room to feed the fire , so that at a certain point during the process that would start to drop , because the stuff that's going out and filling the house is oxygen-depletion , nothing coming back into the fire . So this is all going on .

Speaker 2 30:33

So you set that fire . You set that fire with a modern fire retardant treated armchair . It would burn for a period of time , but when the oxygen had only depleted a certain amount , the fire would go out . And then the house is full of what's been produced up to that point , and it would be . There would be quite a lot of carbon oxide and stuff in there . But if you took one that was not treated , which would burn more easily , it would keep burning for a longer period to a lower level of oxygen depletion , more oxygen depletion And because it was doing that , you ended up with a greater amount of product . When that fire went out , the house was full of more smoke , more products . So there are some interesting complexities in the full-scale performance of all those things , which I thought was quite interesting in that set of data that we produced , which is published , in fact .

Speaker 1 31:23

And what about the toxicity of the halon products from the retardants ?

Speaker 2 31:29

Well , the main thing you've got there is the hydrogen chloride or maybe hydrogen bromide , depending on what on some phosphorus products . So they're certainly irritant without the irritants of the smoke .

Speaker 1 31:42

That was a whole hour of discussion the last time , so let's not go there again . But because I have the final part of the interview we were so far we were talking about these major products , like you even referred to monoxide and CO2 as the major products . There were minor products like HCN and , i guess , the halon products . I wonder now we are considering so far the environment of the fire as related to the , maybe the building in which the fire is happening . But with the growing understanding of the environment as a whole thing , for example , our group is researching what's happening in the surroundings of the building , like in the building next door or maybe in the far remote parts of the building you are at , and obviously the concentrations of these toxic products that cause acute damage , like CO or HCN . They will be very strongly diluted if we are considering building 100 meters away . But still there are products that may come from fire , either carcinogens or maybe some of the super toxicants that we were discussing last time that are produced that could eventually be harmful And like people could be exposed to them .

Speaker 1 32:57

Even far away from the fires And I think an emerging field in building fires this may not be such a huge problem . You very rarely have these huge fires in your cities , but so many cities are next to wildfire areas And you have these massive blooms that actually change the color of your sky . So if the color of your sky has changed , it means the atmosphere your breathing is not clean of anything , so there must be a lot of products in there .

Hazards of Accidental Fire Smoke Exposure

Speaker 1 33:29

So let's talk about this accidental exposure to fire smoke , far away from the fire itself , what you can find in the smoke and what is it produced .

Speaker 2 33:39

Yes , i have something involved with the environmental hazards . So what is acute in the chronic ? So the question is if there's a fire incident near me and I get exposed outside for a day , say to smoke , what are the hazards from that ? And then the other problem is if there's combustion processes going on all the time , or I'm a fire fighter or I'm a fire investigator while I'm coming into contact with these fires or the fire deposits on a repeat basis over my working career , or if I'm exposed to combustion products because there's a factory next door and the combustion process , or busy traffic in the road . where are we going with all that ? So basically , yes , exactly as you say . it's quite interesting If you think of the acute hazards from , say , a fire in a factory or a fire in a burning building , then the way I looked at this one we're producing one of our first standards on this but to think of three zones or hazard zones , and the first hazard zone would be inside the building .

Speaker 2 34:47

And inside the building what we're really concerned about for occupants of the building during a fire is all the stuff we've been discussing Can I survive exposure to this fire plume and get out alive ? Well , in that terms . of course we're most concerned about things like carbon monoxide and solenoid and smoke and all the things we've been discussing , so whether somebody will survive an escape and to some extent the irritants . But once we get outside the building we've immediately got the dilution factor anyone where the smoke plume is blowing and what's happening to the plume coming from the building of 10 to 100 times . So when we do that we find that all these asphyxian gases and these sort of major toxic products the kill people in fires are diluted to more or less harmless levels and they're not really a hazard at all .

Speaker 2 35:35

So if you were to calculate the FED from those , it's very low , negligible , yeah , negligible nothing really , although I'm going to contradict myself now because a colleague of mine , when I asked him about this , was a fireman who used to go and fight wildfires . They didn't wear full BA when they're fighting these wildfires , which is another problem , and I can't remember now . But I did find some data somewhere that fire fighters without BA fighting wildfires can get the significant blood , carboxy and McLovin Not usually enough to cause incapacitation , but they are picking some up . You know there is some there For most people who are in the area around the burning building . It's not really these asphyxian gases we're concerned about .

Speaker 2 36:21

I sort of think that zone one is inside the building . Zone two would be within , say , 100 meters of the building where you might have emergency services or firefighters who are not wearing BA , the managers and not officers . Because they're not wearing BA , they're likely to get exposed to some smoke . So what's the problem there ? Well , i would say the main problem there is the irritant in the smoke . Irritant The smoke is orthopedic and irritants Or acute , a minor mostly . Most places are minor acute health hazard that would cause you to maybe go to sore throat the next day or something like that , and might sting your eyes at the time a bit , a bit unpleasant , But you should make a complete recovery from that . You shouldn't really be expected to have any long term From a single , from a single . So you spend a couple of hours at a fire scene during the national fire .

Speaker 1 37:13

Right , i wrote down 0.5 ppm for acroline , so 0.5 ppm , that's like nothing .

Speaker 2 37:21

You might well . No , acroline is an irritant , because irritancy works over such a large order of magnitude . You could sense it , you could smell the odor and the irritancy affects people at very , very low concentrations . So we are interested in the concentrations of these irritant chemicals , and I can also well that would be good for your chest , your lungs . And I may have mentioned last time I used to be on this air pollution committee when one of the things that was monitored in Britain and London was the particulate pm.10 and pm.2.5 concentration throughout the year on a different , on a daily basis , and what was found was that if you had a peak in air pollution on a certain day where it would go up I don't know factor of three or four , then you would get a peak Two days later you would get a peak in emergency presentations of respiratory and cardiovascular emergencies at hospitals .

Speaker 2 38:18

So obviously even these quite low concentrations are having acute effects on people's health And for a certain part of the population they can be serious , really serious , life-threatening . But most people would only notice relatively minor effects . And if you think of what I've called zone three , which is the sort of rest of the town more than a hundred meters or so from the fire scene , then we're talking , and we're talking about a fire lasting a few hours . Then you're talking about fairly minor effects from burning that smoke . If you smoke , if you can see sort of 50 to 100 meters through the smoke but you can see this , this , some foggy smoke wall , or the visibility is that sort of order then there shouldn't be a serious hazard to people , even even most people with some health problems , but they could potentially be in a small subset if a very large number of people are exposed .

Speaker 1 39:11

And we're talking even for a prolonged exposure of , let's say , half a day .

Speaker 2 39:15

It should be fairly minor , but some it should be . Most people would be pretty minor , if anything , but some people might be sensitive . One of the things that concentrated my mind on this was the Buntsfield form , which was about eight miles from where I live . That few member was where a tank farm caught fire some years ago And I heard something . I thought I heard a noise two o'clock in the morning She's in the winter and I got up . I looked out the window . I thought a lot . It was as if a large vehicle had gone , paused or something , something What had happened in the night . But I couldn't see anything . So I just went back to bed . When I got up the next morning looked out the window , a service enormous , huge smoke plume going , punching up into the sky on , flowing South towards London , and I felt , wow , you know What would happen if that plume came down to ground level . But because there was a temperature inversion and because the plant was fairly buoyant , as it were , fortunately The plume and it ended up going more a sin direction of Southampton . It didn't go over central London .

Speaker 2 40:19

In the end , hardly anybody was exposed to that huge fire , the combustion process , that huge fire . When the wind changed . There were people in Holland who started to complain of problems . So in other words , it wasn't until the plume grounded over a hundred , couple hundred miles away . So anybody really got exposed to that . But it was sufficient , even the dilution . You must have dilution in Holland from far .

Speaker 2 40:42

In I near London It was enough to people were aware of it and effective .

Speaker 2 40:47

On the only time I became aware of it , this fire burned for I don't know a week or two before it was extinguished , whereas I was at work , which is about four or five miles from where the fire is , and when they took all the energy out of the plume and put the fire out for the first time , the we smoke was mixing near ground level and you could smell it even five or six miles away .

Speaker 2 41:07

So I know you work in this area . So the dilution and movement of these plumes is really caught an interesting thing and the sort of target Concentrations people are going to be exposed to . So this is the acute side of it . I think a very interesting area is going to be medical epidemiological studies of people who Nealia or in the vicinity of your world's large wildfires Which have been so much more common in recent years , and a little bit of work starting to come up on Downstream health effects , asthma and stuff like that respiratory problems wildfires also are quite interesting because you have a very large Firefront with not such a huge energy density as it's burning .

Speaker 1 41:50

You know , when you have a fire of an oil tanker it's immense Energy density you have there . The plume is super hot . In forest fires , the plume , of course , it's hot and it can be big enough to create its own weather , but in many cases It's much less . It's not like a plume over an oil tanker . So so maybe this effects of grounding the smoke and mixing , especially if there's wind , maybe these effects may be a little more Prevalence than from a very strong thermal plume over a chemical spill , right . So absolutely .

Speaker 2 42:26

Yes , they're gloomy , absolutely , and that's that's right . So I would think we have a you know now got very large cohorts of people Who have been exposed for days or even weeks to these Diluted plumes . You know that are in there many days in the area and so you know It's an opportunity to really study the effects of these have on their health compared to control groups , and I think we will start to see a lot more Health problems coming out from that kind of area . So I think worry in that sort of situation where you're exposed , maybe for several days or even weeks To these kind of smelly dilute residues left over from large fires in the area , that we might start to see More health problems down the line and I have to take should be taken these very serious .

Speaker 1 43:12

Are there any specific Substances that we should be monitoring tracking ? you've mentioned the PM to 5 pm 10 . Yeah , that's right .

Speaker 2 43:20

So I'll say the particle size is very important because it determines where sonic deposits in the respiratory tract PM 10 is going to be in the sort of more upper airways . When PM 2.5 is small enough to get quite deep down into your lung and cause some Chronic obstructive pulmonary disease or acute obstructive pulmonary disease , that kind of thing Also . These very small particles get into the blood and affect the blood vessels and can cause heart problems . It's exciting . So PM 2.5 , physically as it's , to extent that it's just pure carbon , is of concern . But of course a more concern is the fact , as we've been discussing , contensed onto those particles is going to be your own sorts of pyrolysis and organic products , some of the partially oxidized , the sorts of things we've been talking about sorry , i always liked this comparison that the , the suit particles and the particulate matter acts like delivery Vehicles for all the worst things that happen in the fire all the oils .

Speaker 2 44:19

Absolutely Yes . I mean , like I did some An experiment on this I think I might mention last time once with a simple model which was hydrogen chloride . So when I got some animals to inhale hydrogen chloride gas the mice this was , then they had strong effects on the upper respiratory tract and their nose , you know . So they've got these RD50 response . But when I generated the high HCl as an aerosol of aqueous Hydrogen chloride acid , particle acid mist of reciprocal size about what I think was my point , five microns , monodisperses atmosphere , then I got lots of lung inflammation because because the small particles carry , carry the stuff down . And When I other experiments I've done with smokes , i've had lung problems with animals where they'd been smoked particles .

Speaker 2 45:12

So so the smoke part of the very important , as you say , as condensing points to pick up and carry these nasty chemicals down into the Into the lung . Well , once they get there , of course , if you look at the lung of a cigarette smoker , apportion them will be removed , but a portion stay there forever And so that those toxic effects locally to the cells in the lung can carry on . And of course the main site of lung cancer Is the tracheal bifurcation where the air flowing into the lung has to go two ways , split into two directions , to each lung And there's a sort of deposit point where particles get deposited . That's one of the key sites . So so where you've got got the genetic chemicals in the smoke which you will have From wildfire smoke or any other these smokes we've been discussing , then they can be deposited there .

Speaker 2 46:03

But it's as I say , a single incident isn't really going to give you enough to cause problems . What's the problem is going to be if you , if you're exposed to these atoms , who's ever a prolonged period , and that's where we we're interested , then , in things like the dioxins , the aromatic hydrocopy , aromatic hydrocarbons that are in the smoke .

Carcinogenic Substances in Fire Smoke

Speaker 2 46:23

Would you like to talk a little bit about the carcinogenist ?

Speaker 1 46:25

Yes , please . I was . I was about to ask if we have already identified some of , let's say , super carcinogenic , carcinogenic particles like the stuff that is is worse in the fire smoke Produced low content , but it's very dangerous .

Speaker 2 46:39

So just as an organization called the IARC It's an international classification scheme for carcinogens , yes , and it's individual Substances and their extent to which they're carcinogenic , and there's a thing called the IARC classification scheme on their group , according to their activity . So so something the same group one Is something that's been demonstrated as carcinogenic to humans , and then you've got group two , and group twos is group to a , probably carcinogenic to humans . True to be is possibly carcinogenic to humans . Growth through is not identifiable as carcinogenic . And group four is probably not Carcinogenic . And this is all both still an epidemiology , you know . So it's . That's why there's certain on some uncertainty with some of these clutch again . So what we're particularly concerned about is anything in group one on 2a and , to start lesser extent , press group 2b .

Speaker 2 47:35

Then , when we look at the sort of things that come off in fires , i've sort of classified these according to their composition . So one category is substances containing carbon and hydrogen , with or without oxygen . So these are hydrocarbon , e type materials or aromatic materials . Some of them have got partially oxidized aldehydes and things like that . And in that group you've got formaldehyde , which is the simplest Aldehyde , hco , which is a known carcinogen , and that's a very common product That's always found , and it's typically you have mentioned , this appeared as soon as you've introduced the oxygen to the tube furnace .

Speaker 2 48:14

Absolutely .

Speaker 1 48:14

Yeah , and it came from burning a base polypropylene , so it's not that the substance was very .

Speaker 2 48:22

Particularly comes from cellulosic material . So wood , all cellulosic material , produces lots of formaldehyde and acrolin , particularly from wood . That's why wood smoke can be very irritant . So formaldehyde is in group one , the quinoline is group three . So you don't really know enough about it , but it's suspected as possible . Then you could also tell the heights of these aldehydes ethylene oxide , buta dot one , three , buta diene And benzene , which is something you've sure you've heard of , which is known cos it's really bad carcinogen direne , methyl stein and then the polyanomatic hydrocarbons . So all these Well known or or suspected carcinogens , and they're all present , they're in their sort of products . It remember I was saying yesterday , nearly all our burning materials will produce that mix to a greater or lesser extent and hydrocarbons would have a tendency to create particles that close rings , and I see most of ring substances in this list .

Speaker 1 49:16

Already are Known carcinogens benzene , that which is the simplest ring .

Speaker 2 49:22

Already It's a nasty one and if you think of something like petrol , gasoline . When gasoline will burn to some extent , which is a fire of gasoline , fire to the extent that it's burning inefficiently , it will form benzene in the combustion . Products will be formed from the smaller molecules , but there's also a certain amount of benzene in already in petroleum , so some of that benzene might escape combustion , just be evaporated when the fuel gets heat up . So that would also apply to word or any any material . The burn will have that mixed . Then you've got substances which have nitrogen in as well as carbon , hydrogen oxygen . Um tobacco , for example , is one , or any nitrogen containing fuel were produced a sudden score .

Speaker 2 50:05

A prilo nitrile , the crilo nitrile is a suspected carcinogen . Ethyl carbonates the carcinogen . And then you've got the nitrosamines Which are carcinogens . Before you heard of nitrosamines , nitro aerines and toluene dyes , a cyanate . So there's some quite awkward chemicals that could come off from those . And then you've got the homogenated materials for PVC or anything with homogenated flame retardant in , of course , the Benz , pyreons and things that were things that we used to use sorry , they chlorinated by funnels that we used to use as coolants in Transformers and things like that . Orally now bound with all these produce or dioxins and Calculated raw products . When they're born , that can be . Some of them can be carcinogens , pcbs for example only created by things .

Speaker 1 50:54

Well , one second for halogens . Recently there has been a major fire of a train in us I think it was East Palestine where they were carrying PVC . PVC monomer and and it would fall into this containing halogen parts right .

Speaker 2 51:12

Yes , a viral chloride monomer is a carcinogen itself , and then you've been . When it burns , you have Various halogenated materials produced from what but one of the most important toxic products . I think you can get his first gene , which is a very powerful long irritant . So there's quite a few things there .

Speaker 1 51:29

That's like that , that's like a biological weapon actually . Yeah , not a great combustion product , okay , so let's . Let's move to the phosphorus . You mentioned phosphorus .

Speaker 2 51:39

Well , yeah , it's a sure to list , really . but because the famous case with the phosphorus is the tris treatment that was used for children's night wear to make them flame retardant , which is a suspected carcinogen , We were worried about not just the carcinicity but the potential neurotoxicity of some of the organic products that can be released from phosphorus-containing

Hazards and Concerns of Fire Contaminants

Speaker 2 52:01

materials . in nitrogen , phosphorus-containing something , There is something that needs a lot more research . we don't know much about it . Basically , when you have phosphorus as a material in your materials , burning , most phosphorus ends up as phosphorus pentoxide and then phosphoric acid .

Speaker 2 52:18

when you burn with something containing phosphorus , which is a lot but is relatively not too dangerous , But there is some evidence that a small proportion does come off as organic nitrogen phosphorus materials . So it's an area that needs more research , but it's a concern . And then we haven't finished yet , because the other thing you can get there are metals chromium , nickel , molybdenum , antimony trioxide , which is used in some materials , Or , after you can let some of these materials can be given off in a small amount in certain fuels , so in wood and coal and things like that .

Speaker 1 52:54

What about if you aluminum substructures , for example facades ? like aluminum is widely used in construction and I often see if I'm having a very severe fire test of aluminum structure , there's nothing of it that's left after a fire , after a very big fire , so I assume it's in a way . is that dangerous in some ways ?

Speaker 2 53:14

Because there's a debate about how much aluminum actually combusts during the fire and put in oxidizers and how much it actually adds to the heat release which is something people talk about , but oxides of aluminum are not really that toxic . So I went to a big fire once , or in a hotel in Egypt where they'd been , an aluminum facade had burned And what my memory from that is seeing like Dalek Selic tides with molybdenum , else in solidified aluminum on the ground .

Speaker 2 53:44

You know where they'd all run down and then solidified on the ground . Yeah , so this is a mine . It tends to be a fairly minor concern in the metals , but they are there . And then in tobacco smoke you can actually get radioactive polonium because it's in the tobacco when it's grown , in the soil , where the tobacco's grown And what's reminding is a more concern recently from far instance , are mineral fibers And obviously if you've got asbestos in your fire , the breaking up and some of that , those fibers can get broken up and entrained into the plume and deposited them down the countryside or inhaled by people who are nearby .

Speaker 2 54:18

And of course asbestos is a known carcinogen problem .

Speaker 2 54:22

Ceramic fibers as well , ceramic fibers , which are asbestos like , if you like , in the composition , because the problem with these is that if you inhale them while they get deposited in the lung , the lung has a mechanism for cleaning itself and the mucus that comes up out of the lung is the way that particles are deposited along a cleaned out , and particles that get deep into the lung are removed by a different mechanism .

Speaker 2 54:45

So if you get little particles that are as far as the alveolar region of your lung , then that's removed by little cells called macrophages , blood cells which are like a little enneba . They come and engulf the particle and try and carry it away to disposals to keep your lungs clean , and to some extent that works . But when you get asbestos in there , then the macrophage can't absorb the particle because it's like a long , thin spike . And I've seen photographs of this where you end up with three or four macrophages on a fiber of asbestos , looking like kebabs on a stick , and what happens then is that you've got a whole rupture in the lining of the macrophage , which means that the cellular contents leak out when the macrophage dies , and so you never really get those fibers out . They get stuck in the lung . And not only that , but the product leaked from the macrophages were highly inflammatory . So you get this constant inflammation site for years in the lung , which is why asbestos fibers are so dangerous .

Speaker 1 55:49

It's interesting Dave once added that to tobacco filters in the 60s . How horrible is that , when these properties were not known .

Speaker 2 55:58

No , that's right . Celerica is another problem . So one of the problems that followed the World Trade Center which was rather different in some files was that you have the building collapse . You had a huge cloud of cementitious dust If you remember seeing those videos of the time And so people inhaled these mixtures of fibers and dust particles and all sorts of things in And then down down the line . Some of the firefighters in particular survived the World Trade Center event . I've got a developmental source of lung problems and the deposits in the lungs from that one incident . So that's another concern .

Speaker 1 56:37

And how about lead ? I think after Notre Dame Cathedral fire there was considerable amount of interest in lead poisoning around because the structure , the historical structure , has used lead as a construction and joint material and it just evaporated in the fire .

Speaker 2 56:55

Well , if you inhale it it's a problem , but it's more likely to be a problem by ingestion . That would be deposited all around and then it might get involved in food You know , vegetable growing food or something like that . Suddenly , with dioxins and things , they can contaminate vegetables and things in areas that have got contamination . I wouldn't have thought inhalation of lead was too big a problem , but it's one of the ones I've just listed . So in theory , yes , it could be an issue .

Speaker 1 57:23

Okay , david , we went into a loophole of this guy and I'm having huge fun listing all these chemicals and learning about them , but the point is firesome and far away from the fire , you're most likely not inhaling , in a single event , a significant dose of that . Of course , it may vary within the population and you may be at extreme risk at some point and then probably it's not very good . But it's especially important for people like investigators , firefighters , fire researchers , who are exposed daily to those substances which add up and increase .

Speaker 2 58:05

Yes , we should be more careful The two times we should be more careful . One is when we're actually conducting the tests . We should make sure we're not exposed to the smoke and we have reasonable respiratory protection or separation . But particularly when you go in afterwards to clean up and take samples and fire investigators especially , or firefighters who are going and damping down or cleaning up an event in a dusty , smoky and where they were disturbing the deposited smoke , particulates and other chemicals around , and in fact you can get sick buildings as well . This way I came across cases where if there's been a fire in a building , the building's been refurbished but not properly cleaned and professionally cleaned And so to some extent the smoke deposits and all the sort of paralysed associated with them have been covered up and are still in various ducts and places in the building , and then you can end up with a sick building that that building is going to off-grass those products at very low levels over long periods of time . Some people's health is affected And the one particular case I got involved with was a school where there'd been a fire and the school was refurbished .

Speaker 2 59:15

They went back to work at the school and then a new teacher came to work at that school and over a period of time started to get allergies and various other respiratory problems and things like that , which eventually were linked to the fact that they hadn't done a proper cleanup .

Speaker 2 59:29

After the incident , you know , they were still off-gassing of materials which could be detected in the atmosphere or in the duct work and things like that . So I think in terms of exposure to some of these things like dioxins , the hazards from inhalation at the sea , particularly if you take basic residue protection , it's not a big hazard . I did some qualitative calculations on this once . But what is a big hazard potentially is getting soot and contamination on your hands and your clothes and even put them down the line on your food , or when firefighters go home and they have dirty clothing and then they take it off in the home and dust is spread around the home which has got all these deposits in , and then you're getting long-term exposure of the skin of yourself and maybe even your family , which over a long period of time can be hazardous . I think that's an area of a lot of research interest at the moment . So just dermal and oral exposure , more perhaps than inhalation exposure . What's the inhalation exposure ?

Speaker 1 1:00:33

I will second that . If someone's interested in this and haven't seen the podcast episode with Gavrion about the unsafe fire scene , I'm going to link it into the show notes of this podcast episode . And David on this , I would like to end this interview . It was again brilliant and I have learned a lot . So thank you once again for coming to Fire Science Show to show your knowledge and experience and most interesting histories of research you have conducted . Thank you so much .

Speaker 2 1:01:06

Well , thank you very much . It's been very interesting to talk to you about all this and I hope people find it with some value .

Speaker 1 1:01:12

And that's it . And boy , some value we found definitely in this episode with David Purser . It's such a joy and pleasure to interview people like David who are passionate scientists devoted lifetime of research into understanding fundamental things in fire in a way that perhaps no one else on the planet does pure joy for me and something that I've only dreamt about when I've started the podcast . It's very difficult for me to summarize . This is the final episode with David that closes a four episode cycle of episodes with him on fire toxicity .

Speaker 1 1:01:51

I hope you found the whole series interesting and for me myself it's perhaps the most intense course on toxicity and toxic hazards related to fires I ever had in my life , so certainly a very useful and helpful resource for me . I've learned a lot and I hope that's the same case for you . I know there was a lot of chemistry around and it was not easy A lot of chemicals and names and

Importance of Fire Science

Speaker 1 1:02:21

you had . This world is huge and fascinating and complicated , but it is important . We tend to omit that . We tend to simplify it , maybe sometimes oversimplify it , but it clearly is an important part of fire science and I hope this four episode with David just brought this part of fire science a little closer to you . I hope you'll eventually find and use for everything that has been said in the episode . I wish you that , and that would be it for now . Thank you for listening to the fire science show And guess what ? see you here next Wednesday . Another episode coming your way . Cheers , bye .