User Manual

Siemens Switzerland Ltd

Building Technologies Division

2.1.2. Managing the fire load

Fire risks are largely determined by the fire load of a room or area. The term describes the latent energy which can

be released by the combustion of the flammable material within that area during the outbreak of fire: this

includes not only the furniture and furnishings, but also the wooden construction of the building itself.

Figure 7 Example of excessive fire load

The typical fire load in historical buildings can be classified as 'relatively high’, due to their (wooden) construction

and inflammable furnishings (including furniture, curtains, tapestries and carpets etc.). Care should be taken to

reduce the fire load wherever possible, by maintaining a certain distance between articles of upholstered

furniture, curtains and tapestries etc. and by the use of fire resisting paints (where applicable).

2.1.3. Controlling oxygen levels

At a very basic level, the air supply that feeds a fire can be reduced by ensuring that all separating doors between

different rooms in a building are closed (at least outside the normal opening hours).

A recently developed technique that may be suitable in certain applications is based on reducing the oxygen

content of the air to a point that no longer allows a fire to develop. Normally air contains approximately 78%

nitrogen and 21% oxygen (with the other 1% being made up of argon, carbon dioxide and small amounts of other

gases). By reducing the oxygen levels to between 15% and 16%, combustion can effectively be prevented while at

the same time providing sufficient oxygen for people to breathe. This technique was evaluated in the research

report “Hypoxic Air Venting for Protection of Heritage” by Geir Jensen [6] (published in support of the COST Action

C17 “Built Heritage: Fire Loss to Historic Buildings”) and found to offer certain benefits; however, a number of

significant disadvantages were also identified, including:

· The energy costs involved in continuously generating the nitrogen required

· The associated compressor noise and maintenance costs

· Possible restrictions due to employment regulations