User Manual

Siemens Switzerland Ltd 24
Building Technologies Division
4.3. Extinguishing agents
A variety of extinguishing agents are used, each of which utilizes one (or more) of the above mentioned
mechanisms.
4.3.1. Gas
Gases are fast, highly efficient, electrically non-conductive and clean. Their properties make them particularly
suitable for rooms with high value content. Some types of extinguishing gas rely on the removal of oxygen, while
others rely on chemical inhibition of the combustion process:
Natural gases (oxygen
depletion)
The following natural gases are suitable for extinguishing purposes:
• Carbon dioxide (CO2)
• Nitrogen (N2)
• Argon (Ar)
Mixtures of these gases are also commercially available.
Automated extinguishing systems using such gases (or gas mixtures) rely on the
partial displacement of air (and consequently oxygen) from the protected area.
The concentration of oxygen in air is 20.8 vol.-% and reducing this concentration
to below 13% will stop the combustion process for most combustible materials.
When CO
2 is not used then the remaining oxygen concentration (generally
between 10 and 13 vol.-%) is not life threatening. However, this is not the case if
CO2 is used; as a concentration of as little as 5 vol.-% of CO2 gas can be life
threatening. This has nothing to do with the reduced oxygen content of the air,
but is purely due to the toxicity of the CO2 itself. As concentrations of up to 50%
may be reached in some extinguishing systems, it would be fatal for anyone
remaining in the gas-flooded area.
Chemical extinguishing
gases (inhibition of
combustion process)
Due to their chemical properties, extinguishing agents such as Novec 1230 fluid
and HFC227ea inhibit the combustion process by extracting energy from the fire.
On being released into the atmosphere, these gases form an extinguishing
mixture. A correctly controlled concentration of this mixture extracts heat from
the fire and cools the burning material down to the point where the fire is
extinguished.
For HFC227ea and Novec 1230 fluid, the concentration level used in practice is
below the NOAEL value (Non Observed Adverse Effect Level). It does not
therefore pose a health threat to people present in the protected area. However,
the area should always be evacuated before the agent is released.
4.3.2. Foam
Blanketing the burning surface of a combustible material (either solid or liquid) with foam effectively separates it
from the surrounding air, depriving the fire of the necessary oxygen. The cooling effect of the foam also
contributes to the extinguishing process. Foam is particularly suitable for use in fire extinguishers.