Why do halon fire extinguishers contain nitrogen

Use CO₂ fire extinguishers with caution

CO2 fire extinguishers are very popular in sensitive operational areas, especially in rooms with electronics or IT equipment, because they are extinguished without leaving any residues and therefore little extinguishing damage. A DGUV practical test has now shown, however, that the risk to the extinguishing person is significantly higher than previously assumed: Since CO2 is heavier than air, suffocation can occur, especially in small and narrow spaces - unnoticed as CO2 is colorless and odorless .

CO₂ fire extinguishers contain carbon dioxide, a very effective extinguishing agent whose extinguishing effect is based on the sticking effect. This means that the oxygen content in the atmosphere surrounding the fire is reduced to an effective extinguishing concentration of <15% by volume.

Carbon dioxide (CO₂) is an extinguishing agent that is also electrically non-conductive and consequently does not leave any residue. Therefore, CO₂ extinguishers are also ideally suited for rooms with sensitive clean room technology or rooms with high hygiene requirements.

CO₂ fire extinguishers contain the breath poison carbon dioxide

But carbon dioxide is also an odorless breath poison. It acts on the blood, nerves and cells in the human body. At a concentration of more than 2% by volume, there is a strong increase in the respiratory rate. Associated with this is an increasingly poor supply of oxygen to the body's cells. With more than 4% by volume, circulatory disorders also occur in the brain. There is also dizziness, nausea and ringing in the ears. There is already a risk of suffocation from 5-8% by volume - not as previously assumed from 10% by volume.

Relevant space volume is lower

The previous calculations relating to the total volume of the room with regard to the expected CO₂ concentration in the room must be corrected. A creditable room height of a maximum of 2 m must be expected instead of the actual room height. In order to minimize the risk from the released CO₂, this means: For a person who is in the room to extinguish a fire, there must be at least 5.5 m² of free floor space per kilogram of CO₂ extinguishing agent. In practice this means:

  • A 2-kilogram CO₂ extinguisher requires at least 11 m² of free floor space.
  • A CO₂ extinguisher weighing 5 kilograms therefore requires at least 27.5 m² of free floor space.

So far, the principle has been that the concentration of carbon dioxide in the room air must not exceed 5% by volume. For this purpose, the Federal Ministry of Labor, Social Affairs and Consumer Protection published the following table:

Room volumes and permissible amount of extinguishing agent carbon dioxide (fill weight in kg)

5% limit for volume of carbon dioxide (m³)

maximum amount of extinguishing agent carbon dioxide (kg)

According to the DGUV, new DGUV information is currently being processed by the “Company Fire Protection” department.

Consequences for the extinguishing operation

If the ratio of room size (free floor space) to the amount of extinguishing agent is less than 5.5 m² / kg, the fire must be extinguished from the outside through the open door gap. Then the door must be closed. The fire room may then only be entered after effective ventilation measures or protected with a self-contained breathing apparatus, e.g. B. by the fire brigade. There is great danger here, so great caution is required!

Adapt risk assessment

As part of the risk assessment, the company must check the CO₂ extinguishing agent quantities (fire extinguishers) provided in relation to the room sizes. If necessary, further or other technical and / or organizational measures must be taken (e.g. other extinguishing agents, extinguishing devices that can be operated from the outside, small extinguishing or object extinguishing systems, operating instructions, safety and health protection signs).

Practical tip for fire protection with CO₂ extinguishers:

CO₂ fire extinguishers with carbon dioxide are suitable for fighting fires of fire class B (fires involving liquid or liquefied substances) and fire class C (fires involving gases).

So check in your area of ​​responsibility to see where there may still be portable carbon dioxide fire extinguishers. This applies above all to areas where fires of fire class A (fires of solid substances, mainly of an organic structure, which usually burn with embers) can occur, e.g. in offices.

These fire extinguishers should therefore be replaced as soon as possible due to the dangers associated with their use. Ideally against suitable water, foam or powder extinguishers.

In Austria, the use of portable CO₂ fire extinguishers with carbon dioxide as an extinguishing agent is prohibited in accordance with the Austrian Workplace Ordinance in small, narrow or poorly ventilated rooms.