firefighters used "liquid CO2" - what would this be? 1

[JOM]

An investigation report into a fire in a ship's funnel says taht firefighters applied 8 tonne of "liquid carbon dioxide." The term was used several times.

CO2 sublimates, doesn't it? Is there a liquid form? Is there some way CO2 can be bound to a liquid for firefighting purposes?

Cheers,
John.

 

[kenvlach]

Yes, there is a liquid form at elevated pressures -- mighty convenient compared to solid for emptying from cylinders! Also, at the critical point 73 atm & 31.1 C, the liquid and vapor become indistinguishable.

There are many carbon dioxide phase diagrams on the Internet. The first one I came across shows the solid-liquid-vapor equilibrium or triple point at 5.11 atm pressure & -56.4 C:

http://www.chem.neu.edu/Courses/1131Tom/Lecture25/sld007.htm

 

[aviat]

Carbon dioxide is a common fire extinguisher agent. It is stored as a pressurized liquid and turns to a gas when expelled, it also gets very cold!

http://www.ci.sausalito.ca.us/sfd/prevention/fe-workplace.htm

 

[Montemayor]

JOM:

I can assure you that if liquid CO2 (LCO2) was, indeed, used by the firefighters in question, the substance that landed on the fire was NOT LCO2 but a mixture of CO2 "snow" and vapor (roughly 50% each, by weight).

It is impossible for LCO2 to exist at atmospheric pressure. Normally we store the LCO2 at 250 psig (which requires a temperature of approx. -20 oF). I have applied LCO2 to fire fighting when I had a storage tank handy. It is effective if allowed to contain itself over the fire and literally "drown" it by displacing all available Oxygen. This may not be applicable to some types of fires, however.

All industrially stored CO2 is usually in the LIQUID state - whether in CO2 fire extinguishers or in the normal, 50 lb compressed gas cylinders. The CO2 contained in fire extinguishers and compressed gas cylinders is saturated liquid at the existing temperature - which, at about 85 oF is approximately 1,100 psig, allowing for some dissolved air. Contrary to what kenvlach states, the liquid and gaseous phases are VERY distinguishable at the critical point of 88 oF & 1050 psia. This is easily proven by liquid level gauges and sometimes by shaking a fire extinguisher. The "sloshing" you feel and hear is the liquid inside. When you open the cylinder valve of a compressed gas cylinder containing CO2, the top vapor portion is drawn off, causing a vaporization of the bottom, liquid content. This is clearly viewed on the outside of the cylinder by the creation of a "frost line" at the liquid level. This is the adiabatic cooling effect of the liquid vaporization inside. You get the same effect with other compressed gas liquids such as the Freons, Chlorine, Ammonia, etc. A CO2 fire extinguisher is a totally different arrangement: the cylinder valve has a SYPHON TUBE and what you draw out of it when you activate a CO2 fire extinguisher are the products of the liquid CO2 flashing - CO2 "snow" and Vapor! This is why you have a "horn" on the fire extinguisher: it is used to direct the "snow" onto the fire.

All industrial quantities of CO2 today are transported, stored, and handled as LCO2 at 250 psig & -20 oF. Liquid vaporizers (electric or steam) are used to convert the LCO2 to saturated gas at the point of consumption if the gaseous phase is required (such as in the bottled carbonated beverage industry).

CO2 does not sublimate. Dry Ice (compacted CO2 snow @ -109 oF) does sublime from the solid phase directly to the gaseous phase. Dry Ice is conventionally made by flashing LCO2 in a series of "evaporators" - actually, nothing more than flash vessels - down to a saturated liquid CO2 at 125 psig from which it is fed (or flashed) into a hydraulic press chamber. The chamber collects the produced "snow" and subsequently compresses it into convenient blocks that usually measure 10" x 10" x 12". Another production method is one where the snow is compressed into even more convenient "pellets". I hold a US patent for such a device and process.

I hope the above helps to explain some of the unique characteristics of CO2 and it's application in industry and elsewhere.

Art Montemayor
Spring, TX

 

[unclesyd]

Art,
Used your “Dry Ice” pellets many a time for blast cleaning equipment and process vessels. We had good results on most areas in replacing Hyper Pressure Water Blasting.

 

[Latexman]

unclesyd,

I've never heard of dry ice pellet blasting before this. Who's the industry leaders? I've got an application I'd like to talk to someone about.


Good luck,
Latexman

 

[unclesyd]

Latexman,
Give me a chance to look this up. I'll get back
The outfit was from Louisiana, Baton Rouge I think. They are a lot of peple doing it now.

FYI
We also blasted with corn cobs, nylon pellets, Sodium Bicarbonate, nut shells, and wet ice on a macro scale.

Here are some general information websites about CO2/Dry Ice Blasting.

http://www.coldjetsolutions.com/tech-index.html

http://www.rsg-technologies.com/

http://www.dryiceinfo.com/cleaning.htm

 

[aviat]

Carbon dioxide is also good to purge a fuel tank prior to welding. Discharging a fire extinguisher into the tank, the fuel vapors will be displaced by the carbon dioxide, because it is heavier. Other uses are at:

http://www.occc.com/abc/uses.htm

 

[JOM]

Thanks, Art, for all that info. The fire brigade applied 8.6 tonne of liquid CO2 over two hours before the fire was deemed extinguished. Apparently, water is not to be used in this sort of fire.

The CO2 made its way to the main engine turbo charger which remained full of ice for three days!

Cheers,
John.