An ignition source is any heat, spark, flame or other energy capable of igniting flammable vapors, gases, dusts or materials, and controlling it is one of the main ways to prevent workplace fires and explosions.
An ignition source is anything that can supply enough energy to start a fire or explosion when it meets a flammable or combustible material and oxygen. Open flames and welding arcs are the obvious examples, but ignition sources also include hot surfaces, electrical sparks, static electricity, friction, mechanical sparks from tools or machinery, chemical reactions that generate heat, and even lightning.
Ignition sources are one side of the fire triangle. A fire needs fuel, oxygen and heat at the same time, and removing any one of the three prevents it. In most workplaces, oxygen is always present in normal air and fuel is often part of the process, whether that is a solvent, a fuel tank, grain dust or a stack of cardboard. That leaves control of ignition sources as one of the most practical levers safety teams have, especially in areas where flammable vapors or dusts cannot be fully eliminated.
Many ignition sources are invisible or easy to overlook. A static discharge while filling a drum, a hot bearing on a conveyor or a non-rated phone carried into a tank farm can release enough energy to ignite a flammable atmosphere. That is why ignition source control is built into OSHA rules on flammable liquids, hazardous locations and hot work, and into fire codes such as those published by NFPA.
Welding, cutting, brazing, grinding, torches, pilot lights, heaters and smoking materials all produce flames or sparks. Hot work is one of the leading causes of industrial fires, which is why it is usually controlled through a permit system.
Engine exhausts, steam lines, ovens, dryers, overheated bearings, light fixtures and process equipment can heat a material to its autoignition temperature, the point at which it ignites without a flame or spark. Some solvents and oils autoignite at surprisingly low temperatures.
Switches, relays, motors, extension cords and damaged wiring can all produce arcs and sparks during normal operation or when they fail. Ordinary electrical equipment is not designed for use where flammable gases, vapors or dusts may be present. In those areas, equipment must be rated for the hazardous location, for example explosion-proof or intrinsically safe.
Static charge builds when liquids flow through pipes and hoses, when powders move through ducts or chutes, and when people walk across certain floors. A discharge can easily ignite flammable vapors. Pouring a low-conductivity solvent from one metal container to another without bonding and grounding is a classic cause of flash fires.
Steel tools striking steel or concrete, misaligned belts, rubbing conveyor components and failing bearings can generate sparks or heat. In grain handling and other dusty operations, mechanical friction is a frequent trigger for dust explosions.
Some materials heat themselves. Oily rags can spontaneously combust as the oil oxidizes, reactive chemicals can generate heat when mixed, and damp organic materials such as hay or wood chips can self-heat in large piles.
Forklifts, vehicles and generators bring hot exhausts and electrical systems into work areas. Phones, radios, cameras and flashlights that are not certified for hazardous locations can also be ignition sources in classified areas.
Start by mapping where flammable liquids, gases and combustible dust are stored, used, transferred or could be released. Those are the areas where ignition source control matters most. A hazard identification review should consider normal operations as well as leaks, spills, maintenance and start-up.
Following the hierarchy of controls, the best option is often to remove the fuel or substitute a less flammable material, such as a solvent with a higher flash point. Where fuel must remain, engineering controls such as ventilation, bonding and grounding, rated electrical equipment, spark-resistant fans and dust collection reduce the chance of an ignitable mixture meeting an ignition source.
OSHA's flammable liquids standard requires bonding or grounding when Class I liquids are transferred between containers, because static is so easily generated. Bonding wires connect the containers so they stay at the same electrical potential, and grounding drains the charge to earth.
Areas where flammable atmospheres may exist are classified under the National Electrical Code into classes and divisions or zones. Electrical equipment in those areas must be approved for the classification. Classification drawings also guide where portable devices, vehicles and tools may be used.
Hot work outside designated areas should require a permit, gas testing where flammable vapors may be present, removal or protection of combustibles and a fire watch. Other activities that introduce ignition sources into controlled areas, such as bringing in a vehicle or a non-rated tool, can be covered by the same permit-to-work system.
Lubricate and inspect bearings, keep electrical equipment in good repair, clean dust from hot surfaces and dispose of oily rags in closed metal containers. Good housekeeping removes the fuel that turns a small spark into a fire.
A coatings plant transferred a flammable solvent from 55-gallon drums into five-gallon pails at a filling station. During one transfer, a flash fire erupted at the mouth of a pail, singeing the operator's sleeve. He was not seriously hurt, and a nearby extinguisher put the fire out. The investigation found that the drum was grounded but the plastic-lined pail was not bonded to it, and the operator was wearing rubber-soled boots on a sealed floor. Static charge had built up on the pail and discharged as he moved the nozzle.
The plant replaced the lined pails with conductive metal containers, installed bonding clips at the station, added a dip pipe to reduce splash filling and posted a step-by-step transfer procedure. It also reviewed its hazardous location classification for the area and found a non-rated fan near the station, which it replaced. The event was logged as a near miss with high potential, and the fixes were tracked as a corrective action.
It varies by industry, but hot work, electrical failures, hot surfaces and smoking materials are consistently among the leading causes. In facilities that handle flammable liquids or dusts, static electricity and friction are also common triggers.
The flash point is the lowest temperature at which a liquid gives off enough vapor to ignite when an ignition source is present. The autoignition temperature is the temperature at which a material ignites on its own, with no spark or flame, simply from heat. Hot surfaces become ignition sources when they exceed a material's autoignition temperature.
It is possible in the right conditions, because phones contain batteries and circuits that can produce sparks or heat if damaged or faulty. Most facilities with classified hazardous areas ban non-rated phones and electronics in those areas and provide certified devices instead.
Look for anywhere flammable liquids, gases or combustible dusts are stored, handled or could be released, including during spills or maintenance. Safety data sheets, hazardous location classifications and process hazard reviews will point to the areas that need the strictest controls.
Part of SafetyIQ's EHS glossary: plain-English definitions of workplace health and safety terms.
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