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12 Cards in this Set
- Front
- Back
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Ventilation is defined as? |
The removal of heated air, smoke or other airborne contaminants from a structure, and their replacement with a supply of fresher air |
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There are three ways a fire can be ventilated: |
• Self-ventilation: Occurs when the fire damages the structure of the premises, so that increased ventilation occurs. For example when a roof collapses or a window breaks
• Automatic ventilation: Occurs when pre-installed vents operate, usually in the early stages of a fire. They can be operated by the fire detection system or fusible link devices. Some can also be controlled by the fire service at the scene. This can be a powered ventilation system or roof lights that open at ceiling level
• Tactical ventilation: Is used to assist firefighting operations and requires firefighters to release the products of combustion and allow fresher air to enter |
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Properly used, tactical ventilation can have significant benefits. It can: |
• Assist the escape of occupants and firefighters by restricting the spread of smoke • Improve conditions for firefighters and trapped occupants • Speed up rescue operations and fire attack by reducing heat and smoke • Increase the safety of firefighters by reducing the risk of flashover, backdraught and fire gas explosion • Reduce fire spread and property damage by controlling the movement of hot smoke and gases • Improve visibility |
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The basic principles of ventilation are: |
• Hot gases should be released from the area at the greatest height possible and replacement fresh air should be allowed to enter at low level • The high level vent should be downwind of the low level vent to take advantage of wind induced air flows • The high level vent should be made before the low level vent • If conditions indicate signs of a potential backdraught, the compartment should be ventilated from outside the building when possible • Outlet vents should be protected by firefighters in breathing apparatus (BA) with charged branches |
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Tactical ventilation can be used at various stages of the fire: |
• After the arrival of the LFB but before control is achieved • After control but before fire extinction • After fire extinction |
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Two types of Tactical ventilation that can be employed are: |
Defensive ventilation This is carried out away from the fire to improve access and escape routes for firefighting and searching conditions. It involves the venting of adjoining and outer compartments after the fire compartment has been isolated and suppressed
Offensive ventilation This is carried out to directly affect the fire itself, to limit fire spread and improve conditions within the fire compartment. It also makes the approach route safer for firefighters |
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When the IC is deciding on the overall strategy at a fire, they should consider ventilation from the beginning. If tactical ventilation is required, the objective for its use should be identified before operations begin. The technique adopted will vary depending on the objectives. For example: |
• Ventilation can help clear the route • Ventilation can also be used to remove hot gases and smoke to improve conditions • reduce risk of backdraught |
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To ventilate efficiently, the IC must consider how and where hot gases and smoke will leave the building and fresh air will be allowed to enter. There are two options: |
• vertical ventilation • horizontal ventilation |
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Vertical ventilation is most appropriate when: |
• The fire is in or has spread to the roof space or structural voids • Where there are tall vertical shafts within the building. |
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The advantages of vertical ventilation are: |
• It minimises the risk of a backdraught • It minimises fire spread • It provides rapid smoke clearance |
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The main disadvantages of vertical ventilation are that: |
• Firefighting operations may be required on the roof above the fire • There are fewer opportunities to make a vertical vent |
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Before tactical ventilation can be undertaken the IC must: |
• Undertake a dynamic risk assessment • Make sure adequate resources are available • Identify the wind direction • Decide whether vertical or horizontal ventilation is more appropriate • Select inlet and outlet vents and decide how they will be made • Make sure the outlet vent is covered by a charged 45mm hoseline • Make sure there is effective communication between other firefighters and IC • Consider withdrawing any firefighters inside the building while ventilation takes place • Notify all crew members of the intention to start ventilation • Make an outlet vent first, followed by an inlet vent as soon as possible • Closely supervise the effects of ventilation and make sure progress and conditions within the building are reported |
