Fixed Installations (Non-Water) Flashcards
With regard to fixed CO2 installations, identify the factors that should be considered when determining the type of installation and the quantity of gas required.
(i) the type/nature of the Hazard
(ii) is the hazard enclosed
(iii) size of the enclosed/area/room (to help determine the volume of gas required)
(iv) is the fire likely to spread
(v) the chance of a fire occurring in more than one place at the same time.
State two risks to people from carbon dioxide.
(i) Asphyxiation
(ii) Frost burns
Describe the purpose of smoke and heat exhaust systems (SHEVS).
SHEVS are natural or powered systems used to remove smoke from a building, controlling the smoke layer to a maximum depth below ceiling level to MAINTAIN a CLEAR AIR LAYER above escape routes high enough for people to use without breathing in contaminated air.
They also:
- reduce damage to the building
- remove heat for firefighter safety
- improve visibility for firefighters
- aid in the removal of unburnt products of combustion in the smoke layer, which may have had negative consequences if left in situ.
Describe the principles of operation of smoke and heat exhaust ventilation systems (SHEVS)
(i) On detection for fire/smoke the monitoring system opens the roof vent.
(ii) smoke dampers on the affect floor(s) are then opened.
(iii) this opens a pathway to the smoke shaft/resivour.
(iv) smoke enters the smoke shaft and if using natural methods moves vertically via bouency and out of the exhaust vent.
- If powered mechanically an extraction system will have been triggered which pulls the smoke out of the exhaust vent whilst in turn creating a positive pressure within the building which can slightly open stairwell doors aiding in the replacement of fresh air within the stairwell.
Only dampers on the smoke logged floor(s) should be opened otherwise the SHEV system may move smoke to unaffected floors.
Explain how an inert gas installation operates to extinguish fire and state the precautions that should be in place when the system is activated.
Normally total flooding systems used in data centres and other IT environments.
Consists of a detection and activation systems linked to gas storage cylinders (argon, nitrogen, small amounts of CO2), specially piped into or above the protected risk.
The system then use a blend of gases to create fire suppressant reducing the O2 content of the area <15% but maintaining it above 12% in order to be sufficient at suppressing the fire but not putting anyone in the area at the time of activation in danger of asphyxiation.
Precautions that should be in place at time of activation:
(i) whole building alarm should be activated
(ii) visual alarm should be activated outside the compartment where the system is in use.
(iii) compartment should have a means of extraction to clear the area of the gases.
(iv) the system should have lock off devices to prevent discharge of gaseous substance (eg CO2) whilst people are in the compartment.
Describe the purpose of a pressurisation ductwork system and explain the considerations when determining fire protection for this ductwork when penetrating fire resisting barriers such was walls or ceilings.
A pressurisation ductwork system is a form of mechanical ventilation system using pressurisation as a method of restricting the movement of smoke into critical areas of a building by pressurising the critical area (higher to that of adjacent areas) maintaining its clean air supply.
It applies particularly to protected method of escape routes such as protected lobbies, stairwells and corridors, due to smoke accumulation in these areas rendering them unusaable for evacution.
As well as applying to firefighting shafts serving basements or below gorund installations, due of the difficulties in smoke clearance from these areas as a result of no external vents (windows/doors) being present.
As the air supply creating the pressurisation must be maintained fire dampers cannot be used within the ductwork therefore duct penetrating fire resisting barriers must be fire resisting and attention must be paid to installing the ductwork with in manufactures guidance paying attention to make sure all joints/gaps are seeled with appropriate fire resisting material to stop the leakage of hot fire gases out of the ductwork into any voids..
Describe the types of CO2 installations
(i) Total Flooding
Discharged into an enclsoed space in sufficient quantity to produce a concentration to extinguish the fire.
(ii) Local Application System - (eg printing press)
A firfighting concentration is discharge onto a specific hazard or into a defined area which has no surrounding enclosure.
(iii) Manual Hose Reel System
Manual operated nozzle supplied by a fixed pipe bulk supply.
hazard must be accessible to use of hose reel.
risk of asphyxiation and frost burns.
