A Carbon Dioxide (\(\text{CO}_2\)) fire extinguisher stores the gas as a compressed liquid under immense pressure, typically around 800 pounds per square inch (PSI). When activated, this highly pressurized liquid immediately converts to a gas, creating a powerful, cold discharge intended to smother a fire by displacing oxygen. Directing this suppression tool at a person, even one who is on fire, is strictly forbidden due to the severe and immediate physical harm it causes. The specific hazards range from tissue destruction to chemical asphyxiation, making a \(\text{CO}_2\) extinguisher extremely dangerous to use on a human body.
Cryogenic Burns from Rapid Expansion
The primary danger from a \(\text{CO}_2\) extinguisher is the extreme drop in temperature upon discharge. This cooling effect is governed by the Joule-Thomson effect, where a rapidly expanding gas experiences significant cooling. Because carbon dioxide is stored as a high-pressure liquid, releasing it instantly vaporizes the agent and causes it to expand into the atmosphere.
This rapid phase change absorbs a massive amount of heat energy from the surrounding environment, including the victim’s body. The discharged stream can reach temperatures as low as \(-78^\circ\text{C}\) (\(-109^\circ\text{F}\)), the sublimation point of \(\text{CO}_2\), forming particles of solid “dry ice snow.” Contact with this super-chilled gas stream immediately causes cryogenic burns, often called cold burns or frostbite.
Unlike standard heat burns, cryogenic burns damage cell structures by freezing the water inside them. The formation of ice crystals ruptures cell membranes and disrupts blood flow, leading to immediate tissue death (necrosis). A direct blast causes deep tissue injury within seconds, resulting in permanent damage, nerve loss, and potential amputation. Furthermore, the velocity of the discharge drives the super-cooled gas deep into clothing layers, intensifying the cold injury below the surface.
Physical Trauma Caused by Discharge Force
The physical force of the discharged \(\text{CO}_2\) stream carries a significant risk of severe mechanical trauma. Because the agent is held at high pressures, the sudden release results in a powerful kinetic blast. This high-velocity stream is strong enough to cause direct physical injury to soft tissues.
If the discharge is aimed at the head, the sudden pressure wave can easily rupture the eardrums, leading to immediate hearing loss. The force can also cause severe eye trauma, including corneal abrasions, retinal detachment, or permanent blindness, as the blast impacts the delicate structures of the eye. Beyond auditory and ocular damage, the kinetic energy of the stream can cause deep bruising, lacerations, and internal hemorrhaging to the skin and underlying muscle tissue.
The Danger of Oxygen Deprivation
\(\text{CO}_2\) extinguishers function by smothering a fire, reducing the concentration of oxygen (\(\text{O}_2\)) below the level required for combustion. When aimed at a person, the dense carbon dioxide gas rapidly displaces the breathable air surrounding the victim’s head. This creates an atmosphere of chemical asphyxiation.
The normal concentration of \(\text{O}_2\) in the air is approximately 21 percent, but a \(\text{CO}_2\) discharge can swiftly lower this to dangerous levels. Exposure to concentrations exceeding 10 to 15 percent can cause confusion, dizziness, and rapid loss of consciousness within minutes. If the \(\text{CO}_2\) concentration reaches 17 to 30 percent, it can lead to convulsion, coma, and death from asphyxiation within a single minute.
Safe Response Measures for Human Fires
The safest immediate action when a person’s clothes catch fire is the “Stop, Drop, and Roll” technique. The victim must immediately stop movement, drop to the ground, and cover their face with their hands. They should then roll repeatedly to smother the flames against the ground, cutting off the fire’s oxygen supply.
If the victim cannot perform this action, the safest alternative is to use a heavy blanket, rug, or coat to smother the flames. The material should be wrapped tightly around the person to cut off the oxygen, and the fire should be patted out rather than beaten. Water can be used to douse the flames only if the fire is not caused by an electrical source or flammable liquids.
If a fire extinguisher must be used as a last resort, a water or foam extinguisher is the only appropriate type, but even these should be directed sparingly at the base of the fire. The primary goal is to extinguish the flames through smothering, minimizing the individual’s exposure time and avoiding the devastating secondary injuries caused by \(\text{CO}_2\) discharge.