Fire fighters

by Lawrence A. Weaver, CSP

They might as well add “firefighter” to your job title with all the problems you have to deal with on a daily basis. But, hopefully, you’ve escaped the statistics and haven’t had to fight an actual fire on your jobsite.

OSHA statistics report that fires kill 200 workers and injure more than 5,000 annually. Fires also cost businesses more than $2.3 billion a year. Even if a fire has never affected you, these numbers should illustrate the havoc that fires can wreak on people’s lives. Here are a few real-life examples of how devastating a fire on a jobsite can be.

Refueling fuels fire
At a road construction site, two employees were tamping the bottom of a trench. When the tamper ran out of gas, one employee carried it to the top of the trench to refuel it. The other employee stayed in the trench and took a cigarette break. Some gas spilled as the tamper was being filled. Since the vapor density of gasoline is heavier than air, the vapors sought the lowest point and drifted to the trench floor.

When the fumes reached a source of ignition — the lit cigarette — they ignited and then ran back to the source — the gas can and tamper on top of the trench. The person in the bottom of the trench received minor burns to his hands; the employee on the top refueling the tamper received second- and third-degree burns to his hands.

Vapors cause flash fire
At a ship repair site, a Coast Guard vessel was being refurbished during the Persian Gulf War. One particular job involved rebuilding compartments used to store refrigerated foods. A subcontractor was installing rigid foam insulation by gluing it to the hull of the vessel.

The glue was highly flammable and did not meet the specifications of the Department of Defense for use on the vessel. A Material Safety Data Sheet was not requested nor supplied to provide product warnings.

The vapors were very strong so the subcontractor used a box-type fan to ventilate the hold of the ship. At the end of the day, the crew unplugged the fan; simultaneously, someone struck a bare light bulb with a broom handle, breaking it. One or both actions ignited the flammable vapors that caused a flash fire resulting in over $50,000 of damage to the vessel and destroyed over $50,000 of food. The Coast Guard sued the contractor.

Tarpaper fire kills two workers
At a high-rise municipal building under construction, two employees working from a suspended scaffold were welding on the outside of the building which was covered with tar-based roofing paper. A fire watch had been assigned to the job, but he had gone to lunch. Sparks and slag fell from the welding operation onto the side of the building and ignited the tarpaper. The fire quickly spread until the whole side of the building was in flames. When the two welders realized the building was on fire, they attempted to raise the suspended scaffold to the roof to escape the flames. The scaffold went to the top and the two welders merely had to step over a parapet wall to escape the flames. Smoke inhalation, however, rendered them unconscious and they died on the scaffold at the top of the building.

Construction increases fire risk
Interestingly, fire risks are greater while buildings are under construction, including repair and demolition, than for completed structures. Data from the National Fire Protection Association shows these risks occur because buildings under construction usually have one or more of the following risk features:
• absence or impairment of fire suppression systems to prevent rapid fire spread
• lack of compartmentalization to prohibit fire spread
• greater concentration of flammable or combustible material than in finished buildings
• inability to detect fire in early stages because smoke or heat detectors are not yet installed
• exposed combustible structural elements.

In order for a fire to occur, there must be three elements present: fuel, heat and oxygen. A fourth element, a combustion chainreaction (a chemical reaction that causes the flames), keeps the process going.

Fires are classified by types.

Class A fires are those that involve combustible materials that leave an ash. They include wood, plastics, cellulose, paper, and cardboard.

Class B fires are fueled by gases, greases and flammable and combustible liquids. Examples of Class B fires include gasoline, kerosene, varsol, diesel fuel, and liquefied petroleum (LP) gas.

Class C fires are those in energized or potentially energized electrical equipment such as electric motors, switch boxes, and transformers.

Class D fires are fueled by combustible metals such as magnesium, potassium, aluminum, zinc, and sodium.

To control or extinguish fire, any one of the four elements must be removed. Portable fire extinguishers address one or more of the four elements.

Heat can be removed from a fire with water and to some degree by a carbon dioxide fire extinguisher. Carbon dioxide, however, works primarily by reducing the oxygen content, essentially smothering the fire. Dry chemical extinguishers attack the combustion chain reaction, reducing the oxygen to smother the fire and also provide cooling and radiation shielding to minimize heat transfer.

Foam extinguishers work by floating foam on the surface of the liquid and producing an air-impermeable or excluding barrier that also provides cooling. Halon extinguishers work by breaking the combustion chain reaction, although the exact mechanism is not fully understood.

The oldest type of these halon extinguishers, once in widespread use, contained carbon tetrachloride, an effective extinguishing agent but one with extremely toxic health effects. OSHA now prohibits its use. Other halons include 1211 and 1301, also no longer in widespread use and banned by the Montreal Protocol because of their ozone-depleting characteristics.

Metal fires are best fought by special agents that break the combustion chain reaction. Depending on the applications, one or more of these types will be needed on all construction sites. 

Fix the cause, stop the fire
The following list provides some of the more commonly encountered fire causes on construction sites and ways to prevent them.

• Minimize accumulation and storage of combustible building materials and avoid storage in areas where structural steel is in place but has not had a fire retardant applied.

• Maintain adequate water supplies for fire-fighting purposes. Ensure that the water service will reach all areas of the building.

• Avoid temporarily enclosing buildings with combustible material such as tarps. If they must be used, ensure they are securely attached and kept away from ignition sources.

• Remove wooden form work for concrete as soon as possible after pouring concrete.

• Apply fire retardant as soon as possible to structural steel and other components of the facility.

• Maintain good housekeeping to minimize accumulation of scrap and debris, including lumber and cardboard.

• Control welding and cutting operations by using a permit system that requires a fire watch and fire extinguishing equipment. More than one fire watch may be needed, such as above and below a roof.

• Closely monitor the use of temporary heating devices, including solid fuel and liquefied petroleum gas heaters.

 • Store, handle, and use flammable and combustible liquids in accordance with Material Safety Data Sheet recommendations and OSHA requirements.

• Store roofing materials for hot tar or asphalt-based roofs in a non-combustible container or in a non-combustible location.

• Locate gas and electric systems before digging, cutting or doing any activity that might compromise their structural integrity.

• Control the areas where smoking is allowed on the jobsite.

Editor’s Note: Lawrence A. Weaver III is a safety consultant with L.A. Weaver Co. Inc. in Raleigh, N.C. A Certified Safety Professional, Mr. Weaver can be reached at (919) 832-6242 or by e-mail at Aweaver1@bellsouth.net.

This article was published in the September/October, 2002  issue of Contractor Tools and Supplies magazine.

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