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Dry Ice as an extinguishing agent
For over thirty years, I've been trying to find any research that has been done using dry ice to extinguish fire. The only research I've ever found is the use of CO2 in a gaseous state.
Dry ice is the solid form of CO2, which sublimates at temperatures above −78 °C (−108 °F), which tells me there is substantial BTU absorption capacity.
Dry ice skips the liquid state and changes directly from a solid to a gas.
Being heavier than air, the gas will collect in the lower areas of an enclosed space, which may occasionally be to our advantage when attempting to smother a fire.
Naturally, wind currents will hamper this effect, so outdoor use would be limited, if useful at all.
Does anyone know what would happen if some form of dry ice were introduced into a structure fire?
It amazes me that I haven't been able to find anything, in terms of research and the effects of such.
Imagine thousands of pellets of dry ice being blown into a room/contents fire. Just think about the lack of water damage that is usually associated with normal fire extinguishing techniques.
Please discuss, but please refrain from bashing the idea based on preconceptions, without some form of contrary evidence. If a source can't be cited, please don't respond.
Dry ice is the solid form of CO2, which sublimates at temperatures above −78 °C (−108 °F), which tells me there is substantial BTU absorption capacity.
Dry ice skips the liquid state and changes directly from a solid to a gas.
Being heavier than air, the gas will collect in the lower areas of an enclosed space, which may occasionally be to our advantage when attempting to smother a fire.
Naturally, wind currents will hamper this effect, so outdoor use would be limited, if useful at all.
Does anyone know what would happen if some form of dry ice were introduced into a structure fire?
It amazes me that I haven't been able to find anything, in terms of research and the effects of such.
Imagine thousands of pellets of dry ice being blown into a room/contents fire. Just think about the lack of water damage that is usually associated with normal fire extinguishing techniques.
Please discuss, but please refrain from bashing the idea based on preconceptions, without some form of contrary evidence. If a source can't be cited, please don't respond.
Replies to This Discussion
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Permalink Reply by Ben Waller on
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Reasons that solid CO2 isn't a common extinguishing agent...
It is difficult to pump solids in comparison to a gas or liquid - even finely divided solids. The more finely divided the solids are,the less easy they are to keep in a focused stream once they leave the nozzle of the extinguisher.
Freshly-sublimated CO2 is very cold, so it tends to sink. That puts it on the floor, instead of at the ceiling where it will do the most good.
CO2 flooding at the floor level has the potential to asphyxiate victims that otherwise might survive.
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Permalink Reply by joemac on
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Thank you.
I understand that under still ambient conditions, flooding will occur, however, it is anything but still in the turbulence of a room/contents fire. As to the asphyxiation, discretion would rule where viable victims might still occupy the structure. Hopefully, a thorough search has been completed.
Otherwise, anyone in the structure would have succumbed to the environment, already.
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The problem is that if the search has been done, the fire would already be attacked - and in most cases extinguished - if the extinguishment media was water or Class A foam. In that case, no CO2 flooding would be needed.
There is also no way to protect the search team with CO2 flooding as a hoseline does with water or foam, so combining CO2 solids with a search would unnecessarily endanger the search team.
Cold flooding at floor level wouldn't necessarily be turbulent or create a lot of turbulence, as the cold CO2 would simply sink.
Even if there was additional turbulence, the end result would be cold CO2 at the floor level - the same level where any unconscious or incapacitated victim will be lying.
The other problem is that effective use of CO2 requires an enclosed space, so CO2 sublimiation is likely to be ineffective in any space that has been ventilated.
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Ben, I appreciate your responses, I really do.
I have to ask you, do you have anything other than conjecture to support your stance?
I've gone around and around over the years with several other firefighters, and all I've ever heard is speculation as to why they think it wouldn't work.
I'd love to see whatever research has been done using various forms of dry ice in real-world conditions.
Most living space has myriad surfaces on which pellets, chips, cubes or whatever shape, could rest, It's not like every piece would make its way to the floor. What happens if an involved space is blasted with dry ice? Does anyone actually know? Where are the results of studies?
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There are other problems with dry ice, too. The first is that keeping it in the solid state requires refrigeration, which adds cost to fire suppression. Just manufacturing the CO2 increases fire suppression costs.
Class A foam is a much more efficient extinguishment agent than CO2 for structural fires. It's less expensive, it doesn't require refrigeration, and we have plenty of real-world experience that shows it works.
I have seen studies with CO2 in the gaseous state, which is actually more effective than dry ice, since it doesn't have to sublimate before it displaces oxygen as does CO2. Those studies show that CO2 requires an unventilated space and enough CO2 to flood the entire space in order to extinguish a room fire. Dry ice has a longer response time than CO2 gas, as it has to sublimate into a gas in order to suppress the fire.
There are plenty of studies on CO2 as an extinguishing agent, going all the way back to the US and Imperial Japanese naval damage control studies in the 1930's and 1940's. The benefits and limitations of CO2 as an extinguishment agent are discussed with a lot of detail in the book Shattered Sword, by John Parshall and Anthony Tully.
As for small dry ice pellets not making it to the floor, that's not the point. CO2 in it's solid form isn't an effective extinguishment agent. CO2 must necessarily be a gas in order to displace oxygen and extinguish the fire. When solid CO2 sublimates into CO2 gas, it is very cold. Cold gases sink - in other words, the gas tends to sink to the floor, regardless of where you inject pellets of CO2 solids.
Basic physical principle - heat rises, cold sinks.
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CO2 has another problem - it's a greenhouse gas.
CO2 has a vapor density of 1.5. It's heavier than air - so it sinks.
CO2 sublimates at approximately 88 degrees F, which means it will be a gas at temperatures far below room fire temperatures.
One other thing - water damage isn't the primary problem from building fires - fire damage is. "You can dry out water damage. You can't un-burn a building." Alan Brunacini
Class A foam greatly reduces the amount of water damage by reducing the amount of water required for extinguishment. Compared to CO2 as an extinguishment agent for Class A structure fires, Class A foam wins, hands-down.
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In other words, no, you don't have anything other than conjecture, or comparing CO2 gas to class A foam.
Ok, then.
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Permalink Reply by Rob Vest on
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Sorry Joe, but I have to agree with Ben on this one. I agree that there probably haven't been any studies to support Ben's stance. You just need to look at the physics and probabilities of what will occur. We don't need a study to show that direct flame contact will burn our skin, we just know it does.
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Did you actually look at any of the sources I linked?
Have you ever read Shattered Sword? I doubt it, because it includes not only the results of the engineering of CO2 suppression systems by both the U.S. and Japanese navies, it also covers the reasons why those systems failed to actually do what their designers thought they'd do - extinguish fires as designed.
There are several practical reasons why Class A foam is a better structural fire extinguishing agent than CO2 - any form of C02.
Good luck proving otherwise. It will take disproving a few basic laws of physics while you're at it, but congratulations in advance if you're able to do so.
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Permalink Reply by Jack/dt on
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Likewise I agree with Ben, he certainly has the experience and (clearly) the knowledge. But, in terms of something OTHER than simple *conjecture* I found the following two links:
Follow the link to continued on page 207
http://books.google.com/books?id=xiADAAAAMBAJ&pg=PA100&lpg=...
This one might offer some more info -
http://nzic.org.nz/ChemProcesses/environment/14C.pdf
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Permalink Reply by John Crabbe on
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In other words, no, you don't have anything other than conjecture, or comparing CO2 gas to class A foam.
Ok, then.
Imagine thousands of pellets of dry ice being blown into a room/contents fire. Just think about the lack of water damage that is usually associated with normal fire extinguishing techniques
What type of evidence do you really need any more so than what has been discussed? It really is simple physics. It still takes time for dry ice to sublimaze into a gas, whereas compressed CO2 already is in the state, why even consider dry ice?
Now where is CO2 best used in a fire? Typically not in class A material because of the displacement of O2. Class A material will retain heat within the fuel already and once the CO2 is displaced, it doesn't take much O2 for the fire to rekindle. This is why CO2 is best used for energized electrical or class B fuels, or small class A fires, that are not deep seated.
Then take a look at the cost factors alone as to why such an idea wasn't considered nor researched. The cost of dry ice is considerable to that of frozen water (compare cost at any grocery store), now consider that on a grand scale of a structure fire. Then consider what the cost of the equipment which would be needed to use dry ice as an agent and to get it to the scene. Now look at the range of a distrubution system for such an agent, a typical CO2 extinguisher has a range of 4 to 6 feet, whereas water pressure gives you a much better reach. For the most part the cost factor would be too great for a community to handle whereas a quick fire attack with water or class A foam will limit the damage already done.
While serving in the Navy there was clean agent systems like CO2 and HALON in certain spaces, yet even with such systems there was still fire stations with water or foam capability. The spaces covered by such flooding systems were more confined and smaller spaces. Even with the systems there still had to be a back up agent in place like water or foam and such systems were not in place where class A materials were prominent. Such clean agents were in spaces with costly electronics, flammable liquid lockers, or magazines. The cost of maintaining such systems does get considerable.
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Nice links, including discussion of the losses of the Hornet and the Wasp.
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