CO2 fire extinguishers in confined spaces

Status:

completed 04/2017

Aims:

Carbon dioxide is naturally present in small quantities in the atmosphere (breathing air). The average concentration is around 0.035% by volume. It is a non-flammable, non-caustic, non-water-hazardous, colourless, odourless and flavourless gas. Carbon dioxide has an adverse effect upon health and may cause health disorders, up to and including death, even where sufficient oxygen is present in the breathing air (surrounding atmosphere).

Where a CO₂ fire extinguisher is used to fight a fire in a confined space (closed room), the danger to insured individuals could quickly be exacerbated by the sudden increase in carbon dioxide emissions.

Increasing numbers of enquiries from member companies regarding the effects upon and hazards to individuals extinguishing fires in confined spaces have given rise to a need for clarification. At the present time, only mathematical estimations of the diffusion of CO₂ in confined spaces are available.

Activities/Methods:

Practical extinguishing tests with and without simulation of a fire source were to be performed to confirm or disprove the mathematical estimations. The degree to which a concentration gradient arises in confined spaces was also to be examined.

The extinguishing tests were conducted by employees of Total Feuerschutz at the company's site in Ladenburg. 2 kg CO₂ extinguishers and 5 kg CO₂ extinguishers were fully discharged in the tests in two model rooms. The IFA conducted measurements during the extinguishing tests. In order to determine whether a concentration gradient arose, CO₂ sensors were positioned at three heights both within the test rooms and immediately outside them, and the concentration measured.

Results:

In the tests (55 in total) in two test rooms, measurements of the CO₂ concentration at three different heights revealed a concentration gradient rising with increasing height. This concentration gradient is caused by the high temperature differences between the CO₂ as it expands and the surrounding air. This was confirmed by temperature measurements at the three different heights. Based upon the results of the tests, the previous reference dimension for calculation of the CO₂ concentration was changed from the room volume to the room surface area for rooms up to 2 m in height. A comment on the issue was also issued by the In-plant fire prevention and protection Expert sub-committee.

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