Ventilation (firefighting)

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Ventilation is a part of structural firefighting tactics, and involves the expulsion of heat and smoke from a burning building, permitting the firefighters to more easily and safely find trapped individuals and attack the fire. It is frequently performed from the outside of a burning building while the fire is being extinguished on the inside. If a large fire is not properly ventilated, it is much harder to fight, and can build up enough poorly burned smoke to create a smoke explosion or enough heat to create a flashover. Poorly placed or timed ventilation can increase the fire's air supply, causing it to grow and spread rapidly. Flashover from inadequate ventilation can cause the temperature inside the building to peak at over 1,000 °C (1,830 °F). [1]

Contents

Types of ventilation

In general, there are two types of ventilation; vertical and horizontal. Their names refer to the general locations of the intended exit points of the heat and smoke to be ventilated. Vertical ventilation takes place through holes cut in the roof, typically by truck companies during the early stages of a fire in a process known collectively as roof operations, while horizontal ventilation usually takes place through doors and windows. The goal of each is to clear heat and smoke to increase chances of survival for trapped occupants, and/or so that water lines can be advanced into the structure, to more effectively battle the flames. While their goals are similar, their applications are different; both require good timing and coordination so that increased air flow through a structure doesn't contribute to fire spread. [2]

Methods

Positive pressure fan 20191211Compartment Fire Behavior Training and Tactical Ventilation Instructor International Course IMG 8560.jpg
Positive pressure fan

Mechanical fans can be used to provide positive pressure ventilation by breaking or removing windows, skylights or heat/smoke vents on the roof; or by cutting new exhaust vents in the building. If there is no suitable existing hole, firefighters may use their equipment to make one, such as specialized saws for cutting a large hole in the roof. A conical hose-stream aimed around an opening—of a window or door, etc.—entrains smoke and thus increases the exhaust rate of smoke from the space. This is a process called hydraulic ventilation. This strategy might be used when the fire is small and protecting property from smoke damage can be achieved safely. It can also be used more aggressively when a structure is "fully involved" and the smoke is obstructing the nozzleman's view of the hotspots.

High-rise buildings sometimes also incorporate fans to produce a positive pressure in stairwells and elevator shafts to reduce smoke infiltration into those spaces.

When glass windows in a burning structure burst from internal pressure and heat, or the fire burns through the roof, it may be said to have "auto-ventilated" or "self-ventilated."

Negative pressure ventilation is another method of ventilation sometimes used in firefighting efforts. The method of negative pressure ventilation is a process of using smoke ejectors to remove the smoke from a building. [3] Negative pressure ventilation is not used as much as positive pressure ventilation for the reason that positive pressure can move more air throughout the structure and clear out more smoke in a timely manner.

Hydraulic ventilation is another method of ventilation that is very useful if vertical ventilation or positive pressure ventilation is either unsafe or not a feasible strategy. [4] Hydraulic ventilation is done by setting up a hose line on a fog stream and directing it out a window. The air that a fog stream draws in also draws out the smoke and ejects it outside. This method can be useful during overhaul operations as long as there is another hose line in place in the immediate area.

See also

Related Research Articles

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Firefighting jargon includes a diverse lexicon of both common and idiosyncratic terms. One problem that exists in trying to create a list such as this is that much of the terminology used by a particular department is specifically defined in their particular standing operating procedures, such that two departments may have completely different terms for the same thing. For example, depending on whom one asks, a safety team may be referred to as a standby, a RIT or RIG or RIC, or a FAST. Furthermore, a department may change a definition within its SOP, such that one year it may be RIT, and the next RIG or RIC.

This is a glossary of firefighting equipment.

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<span class="mw-page-title-main">Passive ventilation</span> Ventilation without use of mechanical systems

Passive ventilation is the process of supplying air to and removing air from an indoor space without using mechanical systems. It refers to the flow of external air to an indoor space as a result of pressure differences arising from natural forces.

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<span class="mw-page-title-main">Fire damper</span> Type of passive fire protection

Fire dampers are passive fire protection products used in heating, ventilation, and air conditioning (HVAC) ducts to prevent and isolate the spread of fire inside the ductwork through fire-resistance rated walls and floors. Fire/smoke dampers are similar to fire dampers in fire resistance rating, and also prevent the spread of smoke inside the ducts. When a rise in temperature occurs, the fire damper closes, usually activated by a thermal element which melts at temperatures higher than ambient but low enough to indicate the presence of a fire, allowing springs to close the damper blades. Fire dampers can also close following receipt of an electrical signal from a fire alarm system utilising detectors remote from the damper, indicating the sensing of heat or smoke in the building occupied spaces or in the HVAC duct system.

Building airtightness can be defined as the resistance to inward or outward air leakage through unintentional leakage points or areas in the building envelope. This air leakage is driven by differential pressures across the building envelope due to the combined effects of stack, external wind and mechanical ventilation systems.

<span class="mw-page-title-main">Cross ventilation</span> Movement of air through a building

Cross ventilation is a natural phenomenon where wind, fresh air or a breeze enters upon an opening, such as a window, and flows directly through the space and exits through an opening on the opposite side of the building. This produces a cool stream of air and as well as a current across the room from the exposed area to the sheltered area.

References

  1. Feasey, R. "Post-Flashover Design Fires" (PDF).
  2. LaFemina, Fred. "Ventilation Basics" . Retrieved 2011-11-07.
  3. "Negative Pressure Ventilation". Ventry Solutions. Retrieved 2020-11-05.
  4. "Throw Back to Basics: Hydraulic Ventilation". Fire Engineering. 2015-11-19. Retrieved 2020-11-05.