Smoke Control Flashcards
What is the primary cause of deaths in fire incidents?
Breathing in combustion products and smoke
Most deaths are not due to direct contact with flames or heat exposure.
What percentage of fire deaths not directly due to burns is attributed to carbon monoxide?
85%
Carbon monoxide is the primary toxicant in fire-related fatalities.
What are the two classes of toxic combustion products?
- Asphyxiant gases
- Irritant gases
Asphyxiants prevent oxygen uptake, while irritants cause immediate incapacitation.
What is the effect of carbon monoxide (CO) on the body?
Prevents oxygen transport to cells by forming carboxy haemoglobin
This leads to central nervous system depression and potential death.
How does hydrogen cyanide (HCN) compare in toxicity to carbon monoxide (CO)?
HCN is about 20 times as toxic as CO
HCN is produced from burning nitrogen-containing materials.
What is the primary toxicant in poorly ventilated post-flashover fires?
Carbon monoxide (CO)
These fires have a very high yield of CO.
What is the role of carbon dioxide (CO2) in fire situations?
Displaces O2, increasing breathing rate and depth
This can lead to accelerated inhalation of other toxicants.
What happens to oxygen (O2) levels during a fire?
O2 is consumed, dropping from 21% to lower levels
Levels below 17% impair motor coordination.
At what O2 level does a person lose consciousness?
6% to 10%
Immediate revival with fresh air or O2 is necessary to prevent death.
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How does smoke typically travel during building fires?
Smoke travels to locations far away from the room of fire origin through door openings, leakage areas, cracks, and openings around pipes and ducts.
What is the main driving force behind smoke movement in buildings?
The natural driving forces of buoyancy due to a change in density of the hot gases.
What happens to smoke as it spreads and mixes with cold air?
It loses its buoyancy and descends to the floor, a process known as smoke-logging.
What areas can become smoke-logged as a result of smoke spread?
Escape routes such as corridors, staircases, and lift shafts.
What is a critical reason for controlling smoke movement in building fires?
To prevent smoke spread to escape routes, blocking occupant evacuation and hindering firefighting.
What are the main objectives of smoke control systems?
- To limit smoke spread
- Reduce property loss
- Preserve fire resistance of buildings.
How do smoke control systems contribute to the safety of building occupants?
By maintaining an acceptable, smoke-free environment along escape routes for safe evacuation.
What effect does exhausting smoke and hot gases have on fire spread?
It reduces the accumulation of heat, slowing the rate of fire spread.
What is one consequence of reduced accumulation of fire gases?
Avoids danger of flashover due to build-up of explosive gases.
Fill in the blank: Smoke movement is driven mainly due to the natural driving forces of _______.
[buoyancy]
True or False: Smoke-logging refers to smoke rising and remaining in the air.
False
What are the two methods of smoke control?
- Smoke Containment and Exhaust
- Air Pressurisation of Escape Routes
These methods are used to manage smoke spread during a fire.
What is the purpose of the ‘Smoke Containment and Exhaust’ method?
To contain smoke from a fire and exhaust it to the exterior
This method prevents smoke from spreading unnecessarily.
What is the goal of ‘Air Pressurisation of Escape Routes’?
To prevent smoke from entering escape routes
This allows occupants to evacuate in a smoke-free environment.
In which scenario is the ‘Smoke Containment and Exhaust’ method typically used?
When the fire occurs in the same space as the occupants or escape routes
Commonly applied in atrium buildings.
What happens to cold air when a fire occurs?
Cold air is drawn into the bottom of the hot smoke plume as it rises
This increases the volume of smoke and gases.
What role does a down-stand play in smoke containment?
Acts as a barrier to contain hot smoke in a reservoir
Prevents smoke from traveling afar and losing buoyancy.
What is the required clear layer height for smoke safety?
2.5 m
This height allows for clear visibility for escape and reduces heat radiation exposure.
How does the natural buoyancy of smoke affect its removal?
It drives hot smoke through natural vents
Larger areas may require exhaust fans to assist in this process.
Quantity of smoke removed must…
- Equal the quantity of air entering the plume
- To ensure smoke layer remains at a safe level.
What happens if sufficient air does not enter the space during smoke removal?
- Smoke exhaust system will draw air from leakage areas,
- Compromising effectiveness
- Increase in fire size.
At what level should replacement air supply enter to ensure proper buoyancy?
Low level
This allows the air to contact and be heated by the fire or hot smoke.
What is the maximum face velocity of air supply to prevent hindrance to evacuees?
5.0 m/s
Exceeding this velocity may obstruct the movement of evacuees.
What is the minimum clear height below the smoke layer for safe evacuation?
2.5 metres
This height allows occupants to evacuate in a clear breathable layer.
What is the main purpose of maintaining a clear smoke layer?
- To permit occupants to evacuate in a clear breathable layer
- Aid firefighting operations
A clear layer improves visibility and air quality for those escaping.
What is the lowest acceptable temperature of the smoke layer to prevent loss of buoyancy?
18°C above ambient
Maintaining this temperature helps ensure that the smoke layer remains buoyant.
What temperature of the smoke layer can cause severe pain and discomfort to occupants?
More than 200°C
High temperatures from the smoke layer pose significant risks to safety during evacuation.
Fill in the blank: The design hot smoke layer base must be above the heads of people escaping underneath it at a minimum height of _______.
2.5 metres
True or False: The smoke layer should be maintained at a temperature below 18°C to ensure safety during evacuation.
False
The smoke layer must be at least 18°C above ambient to maintain buoyancy.
What is the primary risk associated with open atriums in buildings during a fire?
Smoke can spread rapidly to other floors or accumulate in the atrium
This poses a significant risk to occupants and responders.
What is the height to which smoke curtains drop when activated?
1.8 metres
Smoke curtains are made of flame-resistant fabric.
What are the main purposes of smoke curtains?
- Keep smoke out of occupied spaces
- Help create a smoke reservoir
- Guide smoke towards the atrium roof for exhaustion
This facilitates safe evacuation and easier access for firefighters.
How can smoke curtains be managed when not in use?
They can be retracted and concealed
This feature allows for unobstructed use of the atrium.
What is the function of an air pressurisation system?
To keep areas smoke-free by increasing air pressure
This protects areas like staircases relative to the area on fire.
How does an air pressurisation system help during a fire?
It blocks smoke from entering protected areas
This allows for safe evacuation and navigation for firefighters.
What does the air pressurisation fan do in a smoke control system?
Pushes smoke to exhaust from the building through smoke vents
This is essential for maintaining clear escape routes.
In which situations are air pressurisation systems required to be installed in staircases?
- Buildings exceeding 24 m in height with no natural ventilation in staircases
- Buildings with more than 4 basement storeys where exit staircases connect to the firefighting lobby in the basement
Each staircase must have its own pressurisation system.
True or False: Smoke curtains can only be used in buildings with natural ventilation.
False
Smoke curtains are effective in various building designs.
What is the main purpose of the air pressurisation system in a staircase during a fire?
To prevent smoke from infiltrating into the staircase via gaps and cracks.
What must all doors separating the staircase and occupied spaces be fitted with?
Automatic door closers.
What is the required pressure difference maintained by the air pressurisation system when doors are closed?
About 50 Pa.
What is the significance of maintaining a pressure differential of 50 Pa?
It prevents smoke from infiltrating from the fire space to the escape staircase.
What force is equivalent to a pressure of 50 Pa across a door?
110 N at the door handle.
Why should the pressure differential not exceed 50 Pa?
It will be difficult for the elderly to open the door.
What mechanism is provided to prevent over-pressurisation in the staircase?
An air pressure relief valve.
What happens when the pressure differential exceeds 50 Pa?
The air relief valve opens to allow air to be released to the building exterior.
What is the fan capacity designed to maintain during door openings?
A pressure difference of 50 Pa.
Why must doors on two successive floors and the main discharge door be opened?
To allow occupants to evacuate and firefighters to access the staircase.
What is the minimum air velocity required through an open door to prevent smoke entry?
1.0 m/s.
What is the consequence of not maintaining a minimum air velocity of 1.0 m/s during door openings?
Smoke may enter the pressurised staircase.
Fill in the blank: The air pressurisation system must maintain a pressure difference of _______ between the pressurised staircase and the occupied space.
50 Pa
True or False: The pressure differential across the door helps occupants open the door easily during a fire.
False
What are the two methods of operating pressurisation systems?
Single-Stage Operation and Two-Stage Operation
In Single-Stage Operation, when does the pressurisation fan run?
Only when the fire alarm system has been activated
What is the basic weakness of Single-Stage Operation?
Delay between the start of a fire, its discovery, and the starting of the pressurisation fan
Why is the operation of pressurisation during the early stages of a fire important?
Large quantities of smoke can be generated through incomplete combustion
In Two-Stage Operation, when is the pressurisation fan system in operation?
Whenever the building is occupied
What additional function does the pressurisation fan serve in Two-Stage Operation?
It meets the normal ventilation requirements of the pressurised space
What is a key benefit of Two-Stage Operation compared to Single-Stage Operation?
Prevention of smoke spread during the early stage of a fire
Why are the fan and associated equipment likely to be in good maintenance condition in Two-Stage Operation?
They are in constant operation
What risks do fires in basements pose?
High heat buildup and unexpected floor collapse
Why is adequate air pressurisation needed in basement staircases?
To prevent hot smoke from traveling through the staircases
Where must smoke vents be distributed in basements?
Along the perimeter of the basement
What must be provided for each basement floor?
Separate ducts and vent outlets
Fill in the blank: In a fire situation, the Two-Stage Operation will run in __________ mode after the fire alarm system is activated.
pressurisation
True or False: In Single-Stage Operation, the pressurisation fan runs continuously.
False
