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personnel protection

 FFE Tip 003: Heat Management Techniques

 

The best organization and equipment is useless without highly trained personnel. A properly trained crew will minimize confusion during casualties, increase the probability of proper initial actions taken and enhance the predictability of damage control response and tactics. Vital to the effort, however, is the continuity of personnel. That is personnel assigned to damage control parties should retain that position even if other shipboard duties change. All members of a damage control team should be cross-trained for at least one other position on their team in order to provide frequent rotation. Ideally, everyone on the ship, particularly small ships, should be trained to serve on a damage control team since they may be needed to fight a major fire, flood, conflagration or a chemical biological, radiological attack.

1. Smoke and Heat

Fire can generate compartment temperatures in excess of 2000 degrees F. Skin surface temperatures as low as 160 degrees F will result in second-degree burns if contact is maintained for 60 seconds. Direct exposure to heated air may cause dehydration, heat exhaustion, burns and blockage of the respiratory track by fluid. A firefighter exposed to excessive heat over an extended period of time could develop hypothermia, a dangerously high fever that can damage nerve centers.

 

Hot Air Exposure
200 degrees
300 degrees
380 degrees
400 degrees
650 degrees
Incapacitation 35 minutes, Death 60 minutes
Incapacitation 5 minutes, Death 30 minutes
Immediate incapacitation, Death 15 minutes
Irreversible respiratory tract damage
Death
 

The particular gases produced by a fire depend mainly on the fuel. The most common hazardous gases are carbon monoxide (CO), the product of incomplete combustion and carbon dioxide (CO2), the product of complete combustion. In a smoldering fire, the ratio of carbon monoxide to carbon dioxide is usually greater than in a well-ventilated, free-burning fire. It also carries the vapors of water, acids and other chemicals, which can be poisonous or irritating when inhaled. Smoke greatly reduces visibility in and above the fire area. It irritates the eyes, nose, throat and lungs. Either breathing a low concentration for an extended period of time or a heavy concentration for a short time can cause great discomfort to a firefighter.

Carbon Monoxide (CO) is the most abundant combustion product and is, therefore, the major threat in most fire atmospheres. Exposure to CO results in an oxygen deficiency in the brain and body. Exposure to a 1.3 percent concentration of CO will cause unconsciousness in two or three breaths, and death in a few minutes.

Carbon Dioxide (CO2) works on the respiratory system. Above normal CO 2 concentrations in the air reduces the amount of oxygen that is absorbed in the lungs. The body responds with rapid and deep breathing (a signal that the respiratory system is not receiving sufficient oxygen).

 

HUMAN TOLERANCE TO CARBON MONOXIDE
PPM CO % OF CO INCAPACITATION DEATH
1500 0.15 30 MINUTES 2 HOURS
4000 0.4 15 MINUTES 1 HOUR
6000 0.6 5 MINUTES 10 MINUTES
20,000 2 15-30 SECONDS 2 MINUTES
60,000 6 IMMEDIATE
(ONE BREATH)
LESS THAN 1 MINUTE
 

Oxygen Reduction

When the oxygen content of air drops from its normal level of 21 percent to about 16 percent, human muscular control is reduced. At 10 to 14 percent oxygen in air, judgment is impaired and fatigue sets in. Unconsciousness usually results from oxygen concentrations below 10 percent. During periods of exertion, such as firefighting operations, the body requires more oxygen and increased demands may result in oxygen deficiency symptoms at normal oxygen levels.

Other Fire Gases

Several other gases generated by a fire are of equal concern to firefighters. Toxic hydrocarbon vapors are produced by fuels. Hydrogen chloride (HCl) is produced when polyvinyl chloride (PVC) electric cable jacketing is burned. Hydrogen cyanide (HCN) is produced when chilled water piping insulation is burned. Fluorocarbon refrigerants, such as R-12, R-114, and HFC 134a, are non-flammable and non-explosive, but exposure to flames or hot surfaces will cause these compounds to generate hydrogen chloride (acid gas), hydrogen fluoride (acid gas) phosgene and other poisonous gases.

One or more of three methods transfers heat from a fire: Conduction, Radiation, and Convection.

Conduction is the transfer of heat through a body or from one body to another by direct physical contact. For example, on a hot stove, heat is conducted through the pot to its contents. Wood is ordinarily a poor conductor of heat, but metals are good conductors. Fire can move from one fire zone to another, one deck to another and one compartment to another by heat conduction. In many cases the skillful application of water, typically applied using fog patterns to rapidly coat and re-coat surfaces with a film of water will retard or halt the transmission of heat by conduction. Fog patterns coat surfaces more efficiently than solid streams, reducing run off and the effect on ship stability.

Radiation is the transfer of heat from a source across an intervening space; no material substance is involved. The heat travels outward from the fire in the same manner as light; that is, in straight lines. For example, radiant heat that is absorbed by an overhead will increase the temperature and perhaps enough to ignite its paint.

Convection is the transfer of heat through the motion of circulating gases or liquids. Heat is transferred by convection through the motion of smoke, hot air and heated gases produced by a fire. When heat is confined (as within a ship), convected heat moves in predictable patterns. Hot smoke originating at a fire on a low deck will travel horizontally along passageways, and then upward by way of ladder and hatch openings, heating flammable materials in its path. To prevent fire spread the heat, smoke and gases should be released into the atmosphere.

2. FIRE GROWTH

During its life, a compartment fire normally experiences four different stages: growth, flashover, fully developed fire, and decay.

Growth Stage

In the growth or pre-flashover stage the average space temperature is low and the fire is localized in the vicinity of its origin. High local temperatures exist in and around the burning material(s), and smoke from the fire forms a hot upper layer in the space. Rollover takes place in the growth stage when unburned combustible gases from the fire mix with fresh air in the overhead and burn at some distance from the seat of the fire. Rollover differs from flashover in that only the gases are burning and not all the contents of the space.

Flashover Stage

Flashover is the period of transition from the growth stage to the fully developed fire stage. Flashover occurs in a short period of time and may be considered as an event, as ignition is an event. It normally occurs when the upper smoke layer temperature reaches 1100°. The most obvious characteristic of flashover is the sudden spread of flame to all remaining combustibles in the fire space. Survival of personnel who have not escaped from the compartment prior to flashover is unlikely.

Fully Developed Fire Stage

In the fully developed or post-flashover fire stage, all combustibles in the space have reached their ignition temperature and are burning. Flames may emerge from any opening. Unburned fuel in the smoke may burn as it meets fresh air in adjacent compartments. A fully developed fire will normally be inaccessible by hose teams and require extinguishment by indirect attack.

Decay Stage

Eventually, the fire consumes all available fuel, at which time combustion slows down (decays) and the fire goes out. If a fire self-extinguishes because of a lack of oxygen, as can occur in a sealed air-tight compartment, fuel vapors may still be formed from a flammable liquid which is above its flashpoint, or from pyrolysis of a solid material. If fresh air is then introduced and the fuel-vapor-rich air is still above its ignition temperature, the three elements of the fire triangle are again present and the mixture can ignite explosively. This is known as backdraft. A backdraft is an unusual occurrence.

3. FIRE SPREAD

If a fire is attacked early and efficiently, it can be confined to the area in which it started. If it is allowed to burn unchecked, it can generate great amounts of heat that will travel away from the fire area, igniting additional fires wherever fuel and oxygen are available. Steel bulkheads and decks and other fire barriers can delay but not prevent transfer of heat.

When a compartment is fully involved or post-flashover, the fire may quickly spread to other compartments. It will also spread to adjacent compartments by heat conduction through the bulkheads. Fires normally spread faster vertically to the space above than to adjacent horizontal spaces.

The spread of fire in electrical cableways and the water from firefighting efforts can interrupt power, lighting and communications which serve vital spaces and functions. Even though most older cables in a cable run are armored, fire experience has shown armor does not deter fire in a cable. If fire is allowed to extend to grouped cables, a deep seated fire that feeds on electrical insulation and generates toxic, dense black smoke can occur.

Burning cables that are grouped together reinforce combustion by trapping combustion heat. In some instances, multiple cable trays that are suspended from passageway overheads limit the ability of firefighters to direct hose streams to the source of the fire. Passageways tend to act as ovens trapping heat from a cableway fire and reinforcing combustion. A significant delay can be expected in locating the seat of the fire due to excessive smoke. Only by venting the fire through the deck are these fires quickly controlled and extinguished.

Many fires spread by heat conduction through bulkheads or decks, without a mechanical breach. If fire spreads, cascading casualties occur and damage control parties are driven away from their tasks. Ships have been lost from uncontrollable fires even when associated structural damage was easily survivable. The ignition threshold table, figure 555-1-5 of reference (b) will give you an indication of the amount of time it takes for material to ignite.

Exposure protection involves protecting uninvolved areas surrounding the affected space, including above and below. This protection can be provided by removing combustible materials from the uninvolved areas, but when they cannot be removed, hose streams may be applied. A NFTI or firefinder can be used to find hot spots on bulkheads, decks and overheads. Combustible material may be used as a seal if it is cooled by water fog. If the opening cannot be closed, water spray can be used to prevent heat transfer by convection.

In fighting major fires, firefighters should leave the fire area after 30 minutes (in conjunction with the breathing apparatus alarm) and ensembles recycled to fresh personnel to minimize personnel heat stress. In training, common sense should be used to judge how long a firefighter should be kept in the suit.

When clothing in contact with skin becomes wet, severe discomfort and burns may be experienced by the firefighter. The firefighter should immediately retreat to a safe area for an adequate break to reduce their inner body temperature. The rehabilitation area may be the same area in which standby personnel are staged. The following guidance applies to rehabilitating personnel returning from the fire area:

  1. Be prepared to help them remove the firefighter’s ensemble.
  2. When staged on weather decks, keep personnel out of the sun.
  3. Put them in a cool area exposed to a breeze, or provide a fan to move air. The RAMFAN salt water mister may be used, if available.
  4. Moisten them down with a wet, cool towel over their head, on their face, wrists, etc.
  5. Ensure that each person drinks about 1/2 to 1 liter (about 1/2 to 1 quart) of cold water, such as melted ice water, or other fluid meant to replace bodily fluids.
  6. Monitor personnel during the recovery period for signs of heat exhaustion or other problems.

Size up the Fire

Determine the location of the fire. For large fires involving significant smoke spread, often only a general location can be determined initially. More precise definition will require personnel with breathing apparatus and thermal imagers to investigate further. Discolored or blistered paint or smoke puffing from cracks or penetrations are indications of fire on the other side of the bulkhead. Determine what is burning (the class of fire) and what other combustibles are at risk of igniting. Determine if the fire size warrants portable extinguishers, hoselines, or fixed systems such as sprinklers or Halon.

Determine if and where boundaries should be set to contain the fire, and what systems should be isolated. For large fires, consider the need for a staging area from which to mount the attack. The staging area should include the following characteristics:

  1. Communications capability with Damage Control Repair Station.
  2. Smoke free, safe haven for firefighters.
  3. Adequate room for firefighters and their equipment.

During fire size up the scene leader and attack team leader must evaluate the fire space conditions and select the appropriate tactic to control and extinguish the fire. If access to the fire space is available, a direct attack should be conducted. If conditions in the fire space prevent access, actions should be taken to improve conditions to permit a direct attack.

Direct Fire Attack

In a direct attack, firefighters advance into the immediate fire area (fire space) and apply water directly onto the fire. There are three distinct techniques available during a direct fire attack:

Direct Attack at the Seat of the Fire

When direct access to the seat of the fire is available, the preferred method is to advance to the seat of the fire and apply water directly onto the seat of the fire for extinguishment. The direct attack technique involves application of short bursts (several seconds) of water with a narrow angle fog or straight stream nozzle pattern onto the seat of the fire. The nozzleman pauses and lets the resultant steam pass over and subside. After the steam has subsided, water is again applied in a short burst. The duration of the short burst is a function of the amount of steam production. As steam production lessens a greater duration water burst may be used as the firefighter moves forward and attempts to directly attack the fire or heat source. This technique may be used for boundary cooling. Water should only be used when the firefighter is faced with the fire or when the firefighter can not approach closer due to radiant heat. The practice of using continual water flow from all hoses when making interior entry should be discouraged.

Fog Attack (to Gain Control of Fire)

When entry can be made into the fire space, but direct access to the seat of the fire is not possible, firefighters may use a fog attack to gain control of the fire and delay or prevent flashover. The following conditions indicate the use of fog attack to gain control:

  1. Where overhead gases are burning (known as rollover).
  2. Where the seat of the fire is obstructed and water streams cannot be applied directly to the seat
  3. Where multiple seats of the fire are growing within a compartment such that one seat of the fire would grow out of control while water is being applied to another seat of the fire.

Fog attack is the application of short bursts (several seconds) of water with a medium angle fog nozzle pattern into the overhead gas layer to control the fire. Fog bursts applied directly over the seat(s) of the fire will reduce fire space temperatures and radiant heat and will knock down flaming combustion. During the pause, the team leader checks for flames and directs additional fog bursts until the flames are knocked down. If the initial fog bursts are too long, the wrong fog pattern is selected, or the nozzle is not directed properly, then too much water may be applied onto the hot steel overhead or the hot upper portions of a bulkhead and excessive steam is generated. This excessive steam could force firefighters to withdraw.

Direct Attack from Access

If high temperature denies access to the fire space but the burning material can be reached by a hose stream from an access, water can be applied to the seat of the fire from the access.

The nozzleman may use the bulkhead at the access as a shield. If the seat of the fire can be reached by a hose stream, then the nozzle should be set to straight stream or narrow angle fog directed at the seat of the fire. A smoke curtain can also be hung at the door to shield the attack team.

If conditions become too severe for these direct attack techniques, the attack team must withdraw and use other techniques, such as indirect attack or venting to improve conditions to allow a direct attack.

Venting the Fire Compartment

Venting involves opening an access in the overhead above the fire or cutting a hole in the overhead above the fire to allow hot gases to escape from the fire space. The fire space should be vented only directly to weather or to very large spaces that lead directly to weather. If there is a weather deck directly above any portion of the fire compartment, heat venting should be attempted by cutting holes at least one foot square in the deck.

The larger the hole the quicker the heat and smoke will be vented from below. Similarly, fog nozzles or applicators can be inserted in holes cut into the fire compartment. For safety of hole cutters and firefighters full protective clothing, including the firefighter’s ensemble and hot-work goggles for hole cutters, shall be worn. Holes should only be cut from weather decks or large areas open to the weather, such as hangars and well decks. Wind direction across the deck must be considered to prevent heat and smoke from affecting other vital activities and vital control areas such as the bridge.

Indirect Fire Attack

During an indirect attack, conditions in the fire space prevent firefighters from advancing into the immediate fire area. Water fog is discharged into the space through a cracked open door or a bulkhead or overhead penetration. When heat or other conditions deny access to the fire space, an indirect attack may improve conditions to permit reentry for a direct attack.

The basic technique for an indirect attack is to apply water fog to the fire space for some time, then stop the water flow. Assess conditions in the fire space through the opening using a NFTI to monitor temperatures or by the severity of heat and steam that blow out of the access to the fire space. Otherwise, continue with the cycle of indirect attack and assessing conditions until the space can be reentered.

  1. Do not conduct an indirect attack when people are in the fire space or when a direct attack is underway.
  2. Isolate the fire space during the indirect attack. Keep the fire space isolated between indirect attacks.
  3. A 4 ft. applicator is effective for an indirect attack, but a vari-nozzle with wide angle fog may be preferred for indirect attack to allow for quick reentry and minimal hose handling when conducting the direct attack.
  4. If the location of the fire is known, conduct the indirect attack from a point that allows application of water to the fire. Obstructions around the fire should be considered.
  5. If the fire space is large, it may be desirable to conduct simultaneous indirect attacks from multiple points.
  6. Apply water fog continuously for approximately five to ten minutes for the initial attack.
  7. Since the indirect attack may not extinguish the fire, temperatures in the fire space may begin to increase after the indirect attack is stopped.

It may be difficult to contain the steam blowing out of the access using a smoke curtain or smoke blanket. Once the nozzle is in place, the attack team should position themselves as far away from the access as they can to reduce their exposure to steam, while still maintaining control of the nozzle.

Compared to using a cracked open access for the indirect attack, attacking through a hole cut in a bulkhead or overhead will reduce the amount of heat and steam blowing out of the fire space. The hole should be no larger than necessary to accommodate the nozzle or applicator. Insert the nozzle into the hole and apply water fog into the fire space continuously for approximately five to ten minutes. Then, secure the water flow and assess conditions in the fire space through the access.

Under some conditions it may not be possible to man the nozzle continuously for the desired duration of the indirect attack. If an applicator is used under such conditions, it may be possible to leave the applicator in the hole unmanned, with periodic monitoring, and retreat to a cool area while water is spraying into the fire space. Vari-nozzles are not recommended for use in this procedure.

Active Desmoking

Active desmoking is removing smoke and heat from the smoke control zone between the inner smoke boundary and outer smoke boundary prior to extinguishing the fire; to aid firefighting efforts and reduce smoke spread in the ship. Active desmoking shall not remove smoke and heat from the fire compartment inside the inner smoke boundary (fire space).

Active desmoking is not required for all fires and is used at the discretion of the scene leader. If the initial attack is unsuccessful or if it is likely that the fire attack will go on for an extended period, then active desmoking should be considered. If smoke or heat in spaces beyond the fire space is impeding the attack on the fire, then active desmoking can improve the environment for firefighters.

  1. The scene leader requests active desmoking.
  2. The repair party leader approves and directs active desmoking efforts that are not at the immediate scene of the fire.
  3. The desmoking team implements active desmoking.

Fire and smoke boundaries shall be set prior to establishing active desmoking. Active desmoking may require breaking material condition ZEBRA, if set, along the desmoking flow path. When using passageways and compartments as the desmoking flow path, the flow path for active desmoking should be in as straight a line as practical.

If portable ducting is used, the maximum smoke removal will be obtained by using portable blowers with a suction duct taking suction from near the overhead of the smoke filled compartment. The duct should be secured as high as possible by cinching the smoke curtain around the underside of the duct with spring clamps. The smoke curtain should be raised about one foot at the bottom to allow make-up air to enter the smoke filled compartment.

Successful desmoking may require maneuvering the ship so that relative wind carries the smoke away from air supply intakes. Ships are encouraged to pre-plan active desmoking, include such plans in repair party documentation,(i.e. MSFD) and to practice active desmoking with smoke generators as part of fire drills.

Active desmoking is accomplished in the following order:

  1. Prepare a desmoking flow path.
  2. Rig portable blower.
  3. Establish and maintain desmoking.

A fresh air supply path as well as a smoke exhaust path is required for effective desmoking. Passageways are effective desmoking paths. Ideally, passageways should be selected such that the fresh air supply access from weather and the smoke exhaust access to weather are separated port and starboard, or fore and aft, or both. The smoke exhaust point should be clear of ship ventilation system air intakes.

Doors and hatches must be closed along the boundaries of the exhaust path. Do not include the damage control repair station, staging areas, or areas with equipment sensitive to heat in the exhaust flow path. Installed ventilation to the passageways must be secured or isolated. By placing portable fans or blowers at the exhaust weather access, smoke can be pulled effectively from the smoke control zone, along the exhaust path and out to weather while replenishment air is drawn in from the supply weather access.