User Manual

39
Siemens Switzerland Ltd
Building Technologies Division
5.3.3. Gas/water-combined systems
An alternative to the pure gas systems can be provided by proprietary systems using a combination of gas and
water mist. Releasing additional N2 gas into a closed room, where an embryonic fire has been detected, effectively
reduces the oxygen concentration in the room and extinguishes the fire, while the water mist cools the
combustible material and prevents re-ignition. The fine water mist also serves to provide a smoke scrubbing
function, which reduces the health hazard for people entering the room following an extinguishing event: smoke
inhalation is the primary cause of death for victims of indoor fires.
Such systems provide an excellent solution for archives, as they combine the following major advantages:
· They ensure that incipient fires are extinguished rapidly and reliably.
· They prevent re-ignition.
· They create no irreversible damage to the artifacts stored in the archive.
5.4. Manual extinguishing infrastructure
5.4.1. Fire extinguishers
Fire extinguishers are mobile or portable manual devices designed for preventing incipient stage fires from
getting out of control. The extinguishing agent is expelled under pressure. In some types of extinguisher the
agent is kept under constant pressure, while in others the pressure is generated by releasing a propellant gas at
the time that the extinguisher is activated.
Extinguishing agents include water, foam, carbon dioxide and powder. These substances function in different
ways and are suitable for different types of fires. Fires are categorized into five main fire classes A, B, C, D and F.
EN Fire class Description
A
Solid materials
Solid materials subject to thermal decomposition which normally form embers.
Examples: wood, paper, leather, textiles and coal
B
Liquids
Liquids or materials which melt under heat and only create flames.
Examples: alcohol, oil, wax, resin, paraffin, petrol, paints, tar and acetone
C
Gases
Gaseous materials which are often stored under pressure.
Examples: hydrogen, natural gas, acetylene, methane, ethane, propane and butane
D
Metals
Strongly ember-forming, combustible metals.
Examples: aluminum, magnesium, potassium, sodium, beryllium, lithium and
barium
F
Cooking oils
Combustible cooking oils and fats commonly found in commercial kitchens.
Figure 17 Material fire classes
Notes:
1. In the European norms electrical fires are not considered to constitute a fire class on their own, as
electricity is a source of ignition that will feed the fire until removed.
2. The above table reflects the European classification system. Definitions used by regulatory bodies in
other parts of the world may show some minor differences.
For example in the USA: Cooking materials è Class K
Liquids + Gases è Class B
Electrical equipment è Class C