Fire prevention, hot work and housekeeping

Fire is one of the oldest and most destructive industrial hazards. A plant fire can kill workers, destroy the business and harm the surrounding community. Most plant fires start in predictable ways: hot work near combustibles, electrical faults, overheated equipment such as bearings and motors, smoking, poor housekeeping that lets dust, oil and waste build up, and flammable liquids handled carelessly. This lesson covers fire prevention at plant level. HSE-216 covers hot work in depth, HSE-222 covers fire wardens and evacuation, HSE-312 covers chemical storage, and HSE-313 covers combustible dust.

How fires start and spread

A fire needs fuel, oxygen and heat, and a chain reaction that keeps them going. Remove any one and the fire goes out. In a plant, fuel is everywhere: cardboard, pallets, plastic film, wood dust, flour, oil-soaked rags, hydraulic fluid, solvents and gas cylinders. Oxygen comes from the air, and sometimes from oxygen cylinders or oxidizing chemicals. Heat comes from sparks, hot surfaces, friction, electrical arcs, static discharge and chemical reactions. Prevention means keeping fuel and heat sources apart, and keeping fuel to a minimum.

Housekeeping is fire prevention

Good housekeeping is one of the cheapest and most effective fire controls. Accumulated dust on beams and ducts, piles of cardboard and pallets, oily rags left on benches, waste bins overflowing beside equipment, and stock blocking sprinklers all give a small ignition the fuel to become a large fire. Housekeeping also matters for exits: a fire that would be survivable becomes deadly if exits and aisles are blocked. In plants that handle combustible dusts, such as flour, sugar, wood, plastics and metals, housekeeping is critical because a thin layer of settled dust can fuel a devastating secondary explosion when disturbed. HSE-313 covers combustible dust in detail.

# Fire load of material left near a work area (illustrative heats of combustion, MJ/kg).
heat = {"cardboard": 16, "wood pallets": 17, "polyethylene film": 44, "hydraulic oil": 42}
stock = {"cardboard": 120, "wood pallets": 200, "polyethylene film": 30, "hydraulic oil": 20}  # kg
total = 0
for item, kg in stock.items():
    mj = kg * heat[item]; total += mj
    print(f"{item:<18} {kg:>4} kg x {heat[item]:>2} MJ/kg = {mj:>6,} MJ")
print(f"Total fire load: {total:,} MJ (about {total / 3.6:,.0f} kWh of heat)")

cardboard           120 kg x 16 MJ/kg =  1,920 MJ
wood pallets        200 kg x 17 MJ/kg =  3,400 MJ
polyethylene film    30 kg x 44 MJ/kg =  1,320 MJ
hydraulic oil        20 kg x 42 MJ/kg =    840 MJ
Total fire load: 7,480 MJ (about 2,078 kWh of heat)

Hot work in plants

Hot work is any work that produces flames, sparks or enough heat to ignite materials: welding, cutting, brazing, soldering, grinding and torch work. It causes a large share of industrial fires, often hours after the work has finished, when smoldering material bursts into flame after everyone has left. The first question is always whether hot work can be avoided, for example by using cold cutting, mechanical joining or moving the part to a designated welding shop. If it cannot, a hot work permit controls the job.

In the United States, hot work is governed by OSHA's welding, cutting and brazing standards (1910.252), the fire code adopted locally, and NFPA 51B, Standard for Fire Prevention During Welding, Cutting, and Other Hot Work. OSHA and NFPA 51B require combustibles within 35 ft (11 m) of the work to be moved or protected, openings within that distance to be covered, and a fire watch where combustibles are close by, during the work and for a period afterwards.

NFPA 51B has lengthened the required fire watch over time. Since its 2019 edition it has called for a fire watch of at least one hour after hot work ends, with further monitoring of the area for up to three additional hours as decided by the person who authorizes the permit. Older practice of 30 minutes still appears in some plant procedures and regulations, so check which rule your plant follows, and use the longer period where there is any doubt.

Flammable and combustible liquids

Flammable liquids such as solvents, thinners and some cleaning agents give off vapors that can ignite well away from the liquid itself. Their hazard depends on the flash point: the lowest temperature at which the liquid gives off enough vapor to ignite. A liquid with a flash point below room temperature can form an ignitable mixture at any time. Plants control flammable liquids by limiting quantities at workstations, storing them in approved containers and cabinets, bonding and grounding during transfer, ventilating work areas and keeping ignition sources away. HSE-312 covers storage and handling in detail.

# Classifying liquids by flash point (simplified GHS categories; illustrative values).
liquids = {"acetone": -20, "isopropyl alcohol": 12, "mineral spirits": 40, "diesel": 55, "hydraulic oil": 200}
def ghs(fp):
    if fp < 23: return "Category 1 or 2 flammable (very easily ignited)"
    if fp <= 60: return "Category 3 flammable"
    if fp <= 93: return "Category 4 combustible"
    return "Not classified as flammable (still burns when heated)"
for name, fp in liquids.items():
    print(f"{name:<18} flash point {fp:>4} C -> {ghs(fp)}")

acetone            flash point  -20 C -> Category 1 or 2 flammable (very easily ignited)
isopropyl alcohol  flash point   12 C -> Category 1 or 2 flammable (very easily ignited)
mineral spirits    flash point   40 C -> Category 3 flammable
diesel             flash point   55 C -> Category 3 flammable
hydraulic oil      flash point  200 C -> Not classified as flammable (still burns when heated)

Fire protection systems

Prevention reduces the chance of fire; protection limits the damage when one starts. Plants rely on detection and alarm systems, sprinklers, special suppression systems for hazards such as fryers, paint booths and data rooms, portable extinguishers and hose stations, and fire separations that stop fire spreading between areas. These systems must be inspected, tested and maintained. A sprinkler valve left closed after maintenance, or an extinguisher hidden behind stock, can turn a small fire into a disaster. Impairment procedures, such as tagging a closed valve and arranging a fire watch while protection is out of service, are part of the permit system.

Portable extinguishers are for small fires only, and only for people trained to use them. If a fire is larger than a wastebasket, spreading, producing heavy smoke, or between you and the exit, leave and raise the alarm. Choose the extinguisher for the fuel: water or foam for ordinary combustibles, dry chemical or carbon dioxide for flammable liquids and electrical equipment, wet chemical for cooking oils, and special agents for combustible metals.

Electrical fires and thermography

Electrical faults are among the leading causes of industrial fires. Loose connections, overloaded circuits, failing insulation and dust inside panels create heat long before they start a fire. Infrared thermography surveys, done while equipment is running under load, find these hot spots so they can be repaired during planned downtime. Many insurers expect an annual survey of switchgear, motor control centers and major panels. Simple daily habits also matter: do not overload power bars, do not run extension cords through doorways or under mats, keep panel doors closed and the area in front of them clear, and report any burning smell, discolored outlet or warm plug at once.

Lithium-ion batteries

Lithium-ion batteries now power many plant tools, forklifts, automated guided vehicles and scanners. Damaged, overcharged or poorly made batteries can go into thermal runaway, venting flammable gases and burning intensely, and the fires are hard to put out. Plants control the risk with charging areas away from combustibles and exits, chargers approved for the battery, inspection and removal of damaged packs, and storage limits. HSE-322 covers battery hazards in more depth.