Venting a fire of heat and smoke saves lives, prevents explosions, assists the advancement of a hoseline and channels fire and smoke spread direction, but it can be counterproductive if carried out incorrectly.
Photo credit: Photo by Scott LaPrade
As I noted in part one of this column (November 2012), much is written about firefighting tactics, but not strategy. One reason for that is because tactics – firefighting tasks and procedures – are easy to define. Raising ladders, stretching hose, venting windows and forcing entry are constant and do not change. Strategy – how we use firefighters, apparatus and equipment – is different because it must be flexible. Strategy changes; sometimes in the middle of a firefight.
In part one, I began describing an 11-point expanded system analysis of firefighting strategy by discussing the first four strategies – locate fire, conduct life-saving evacuations, prevent fire spread and confine fire. This column discusses the remainder of the strategies.
5. Ventilate fire – The strategy of venting smoke and heat from a fire building may be ordered to assist any of the other parts of firefighting strategy. Venting a fire of heat and smoke is a very important strategy. It saves lives, prevents explosions, assists the advancement of a hoseline and channels fire and smoke spread. However, venting a burning building is the most complex strategy and can be counterproductive if carried out incorrectly. Improper methods of venting smoke and heat can trigger a flashover, wind-driven fire or rapid fire spread and trap a searching firefighter.
Supporting the hose team
The most common reason to vent a burning building is to assist the advancement of a hose team extinguishing a fire. Advancement of the first attack hoseline is the most important part of fire extinguishment and all strategy must assist this important task. When you extinguish the fire, you stop flame, smoke and heat; save lives; and stop fire spread. There are several venting strategies an incident commander may order at a fire: vertical venting (opening up roof skylights, scuttle covers and roof cutting); horizontal venting (opening up windows and doors); and no venting (at high-rise office buildings to prevent unpredictable smoke movement caused by the “stack effect”).
The strategy of smoke venting has undergone changes as a result of recent scientific studies by Underwriters Laboratories (UL) and the National Institute of Standards and Technology (NIST). These tests, and specifically the UL study titled “Influence of Ventilation in Residence Structures,” provide new and valuable information about venting. They document how horizontal venting provides a vent port opening and allows the entrained air of a hose stream to push heat and smoke out the openings ahead of their advance and speed up extinguishment. This horizontal venting of windows and doors should be coordinated with the advance of the hose team.
In a one-story commercial strip store or when there is a fire in a multi-story building, the incident commander may order vertical venting by having firefighters remove skylights and scuttle covers at roof level. This vertical venting is an effective way to release heat and smoke from a sealed fire area below. It prevents mushrooming and horizontal fire spread. Heat and convection currents always propel smoke up out of a fire area.
Horizontal venting depends on wind direction, but vertical venting is always 100% effective. Horizontal venting is not as effective because there is a 50% chance the wind will blow the smoke and heat back into the building. In some instances, horizontal window venting may create a wind-driven fire that prevents the advance of a hose team. Vertical venting depends on rising convection currents of a fire, so it never fails.
The most effective horizontal venting is “cross venting”; that is, opening windows on two or more sides of a fire area to let wind blow through a fire area and remove smoke and heat with it. All horizontal window and door venting should be coordinated with the hoseline advance. When the hose team has water pressure and is ready to advance on the fire, then horizontal window and door venting should begin.
An important fact about coordinating venting with hoseline advance, the UL study reminds us about, is that horizontal venting begins with forcing the door to a fire area. If the hose team is not ready to advance on the fire after forcing the front door, the door should be closed temporarily to prevent an increase in the fire, a wind-driven fire and a flashover. The door should remain temporarily closed until the hoseline team is ready to advance.
Vertical roof venting of skylights and scuttle covers is different and can be ordered before the hoseline is ready to advance. If a room-and-contents fire is not extinguished and the fire spreads, the incident commander should order a firefighter to cut the roof deck over the fire as close as safely possible to vent the attic or common roof space of fire and smoke buildup. The only time when horizontal venting need not be coordinated with the advance of a hoseline is when a victim is seen or heard calling for help. In such a case, the area is vented, firefighters enter the area and remove the victim before the hoseline is advanced.
6. Extinguish fire – After all the above strategies are considered, an incident commander must decide on a strategy to extinguish a fire. Experience has shown the most successful strategy is an offensive attack. Firefighters enter the building, seek out the fire and extinguish the blaze with a hose stream. This aggressive interior attack is dangerous, but succeeds 95% of the time. Statistics show most fires are extinguished by the first attack hoseline.
Change in strategy
When the offensive interior attack fails, strategy must change. Firefighters are ordered to withdraw and a defensive strategy becomes the alternate strategy. In rare instances, a defensive strategy may be ordered upon arrival by the incident commander at a fire at which a building is fully involved or is vacant or in danger of collapse or explosion. In such a case, a deck pipe or tower ladder stream will first knock down the large flames. After the fire is darkened down, the incident commander may change strategy to an interior offensive attack. This strategy – defensive followed by offensive – will be ordered only when the stability of the structure has been evaluated and assured.
During a defensive attack, powerful master streams can weaken a building with their impact (consider two or more tons of water striking a building at 100 feet per minute) or by tons of water being absorbed into plaster and dried-out wood. Add this to the destruction caused by the fire and it may prohibit an incident commander from sending firefighters inside to overhaul. Instead, master streams may be used continually until the fire is completely extinguished, which may take hours or days.
7. Conduct searches – Searching, like venting, may be ordered any time during a fire. A primary search is carried out before the fire is under control. While firefighters are locating a fire, saving life, stopping fire spread, confining, extinguishing, venting, salvaging, overhauling, preventing rekindle and securing the building, they are also searching for victims.
A primary search is important, but it is conducted at the most dangerous time – before the fire is extinguished, so the incident commander must order a secondary search to be conducted. A firefighter may not discover a victim during the primary search when the fire is raging, but must not overlook a trapped or unconscious victim during a secondary search.
A secondary search is carried out in a safe, methodical and systematic manner after a fire is under control. It involves searching the entire fire building and the area around the building to look for people who might have escaped the fire by jumping out a window.
An incident commander must have a method to conduct a secondary search and assign specific areas to specific companies. This control is necessary to avoid the serious error of not discovering a fire victim and having a police officer or neighbor find a body after firefighters have left the scene. After a secondary search is completed, the incident commander will record the specific areas searched and fire companies that searched the areas on the fire report.
There is one instance when a secondary search should not be carried out – when the building is in danger of collapsing. In this instance, the incident commander announces over the department radio that companies are “unable to complete a secondary search due to collapse danger” and makes a record on the fire report. This record is necessary because of possible legal action if a victim is discovered during demolition. The incident commander may call a structural engineer to evaluate the building before making this decision, but even after the inspection, the incident commander makes the final decision. This non-search strategy is necessary because there have been instances when firefighters sent back into buildings to conduct secondary searches were killed when the building suddenly collapsed.
When ordering searches after the fire is extinguished, any claims by neighbors that someone is still inside the building must be considered important to an incident commander, but the safety of firefighters is more important. A trapped person must be seen or heard before a firefighter’s life is risked.
8. Perform salvage – An incident commander has two strategies to protect property from fire, smoke and water damage: removal and covering. Small valuables can be moved to a safe area or taken out of a building for protection. Large pieces of furniture or machinery that cannot be moved must be covered with waterproof canvas tarps or plastic by firefighters and remain in place. All valuable property removed to safety must be turned over to the owner or police after identification is obtained. This information is recorded on the fire report.
9. Overhaul fire – After a fire is extinguished, the incident commander must ensure that all small spot fires are quenched. At building fires where destruction is limited to contents, firefighters are sent inside to pick apart the burned items and then soak them with a hose stream so fire will not reignite. However, firefighters are not sent inside to overhaul if the fire has destroyed the walls, floor, roof or suspended ceilings and the incident commander believes the structure is unstable. Instead, a watch line is established and firefighters remain beyond the collapse zone as master streams continually wet down the building. This is called defensive or hydraulic overhauling.
10. Prevent rekindle – There are two strategies for preventing a rekindle. The incident commander may decide to remove some types of smoldering material and wet down other types of smoldering material. Mattresses, stuffed chairs, couches, pillows and cushions can reignite. These smoldering items are often taken outside of the building to a hydrant, pulled apart and soaked with water. The wood structure furnishings are wet down in place with hose streams. Concealed spaces have plaster ceilings and walls opened up with pike poles until unburned wood is reached and wet down with hose streams. Other small articles of clothing can be soaked in a sink or tub.
11. Secure building – A burned-out building that is a hazard to the community cannot be left unattended. After a structure fire is extinguished, overhauled and the incident commander determines there is no chance of rekindle, the property must be secured. The responsibility of the building must be turned over to the owner or the police. If the owner or police cannot respond, the building may be cordoned off with yellow caution tape. If valuables were found during the fire, the incident commander must document them on the fire report and turn them over to police officer after obtaining a badge number.
Firefighting equipment activated during the fire must be returned to working order. Fire escape drop ladders or counterbalance stairs must be returned to working positions. Windows and roofs broken open for venting may be sealed with salvage covers.
An important part of any fire is determining its cause and origin. If there is suspicion of arson and an arson investigator is responding, the incident commander may leave a fire company at the scene to ensure continuous supervision of evidence. Some fire departments carry padlocks and chains that have the firehouse telephone number attached. These locks are used to secure the burned-out premises when an owner or police officer cannot respond.
The main objective of any system is to assist the decision maker. This fire strategy system analysis designed to assist an incident commander is an expanded “locate, confine, and extinguish” system. It has been prioritized (except for vent and search) and contains alternative strategies. This system should be changed, expanded and adapted for your fire department.