FactSheet Internal Combustion Engines as Ignition Sources Internal combustion engines present an ignition hazard when used in facilities processing flammable liquids and gases. If flammable vapors or gases are released in these facilities, an internal combustion engine could ignite the flammable materials with catastrophic consequences. Investigations by OSHA and the U.S. Chemical Safety Board (CSB) document a history of fires and explosions at workplaces (oilfields, refineries, chemical plants, and other facilities) where an internal combustion engine was identified as or suspected to be the source of ignition.1 Understanding the Hazard Internal combustion engines, whether fueled by gasoline, diesel, propane, natural gas, or other fuels, can act as ignition sources. Examples include: • Stationary engines such as compressors, generators and pumps. • Mobile equipment or transports such as vans, trucks, forklifts, cranes, well servicing equipment, drilling rigs, excavators, portable generators and welding trucks. • Contractor vehicles and motorized equipment. • Emergency response vehicles such as fire engines and ambulances. • Vehicle-mounted engines on vacuum trucks, tanker trucks and waste haulers. An explosion at a refinery site killed 15 and injured nearly 200; an idling diesel pickup truck was the most likely ignition point. • Small portable engines such as mowers, blowers, generators, compressors, welders and Source: U.S. Chemical Safety Board pumps. This includes hand tools unrelated to Increasing the fuel-to-air ratio also causes pre- a process, such as chain saws, brought in by ignition within internal combustion engines. contractors. Pre-ignition occurs when a fuel-rich mixture in Internal combustion engines require a specific fuel- the cylinder ignites before the spark plug fires. to-air ratio to work properly. Air enters the engine Pre-ignition creates damaging pressure surges through the intake that leads to the combustion and higher engine surface and exhaust system chambers (cylinders). If employers allow internal temperatures. combustion engines in areas where flammable If the temperature of the surface of the engine vapors or gases exist, then the vapors and gases in contact with the fuel/air mixture reaches the can enter the cylinders of the engine along with the autoignition temperature of that mixture, a fire air. Additional flammable material in the cylinders or explosion will occur.2 provides an external fuel source and increases the • Creating sparks. Fuel-rich conditions in an fuel-to-air ratio in the engine. Changes in the fuel- engine can result in incomplete combustion. to-air ratio create ignition hazards by: • Elevating engine operating temperatures. 1 From Bureau of Labor Statistics and OSHA Integrated Increasing the fuel-to-air ratio causes an Management Information System (IMIS) databases, and CSB reports 2003–2010. increase in the energy output which results in 2 The autoignition temperature of a chemical is the lowest increased surface and exhaust temperatures. temperature at which an air mixture of the chemical will ignite without a spark or flame. 1 When uncombusted fuel from the cylinders Whenever possible, do not The OSHA General Industry enters the exhaust system, it can ignite due to install permanently-mounted and Construction standards the hot surface, discharging sparks and flames internal combustion engines contained in Subparts S and K (29 CFR 1910.307 and (backfire). These can ignite flammable vapors in areas where flammable 29 CFR 1926.407) of the Code and gases in the surrounding area. vapors or gases could be of Federal Regulations (CFR) • Causing overspeed and runaway engines. present. define hazardous (classified) locations as areas with: Overspeed occurs when flammable vapors If employers cannot remove and gases in the intake air cause engines to run • Flammable gases or vapors internal combustion engines (Class I) faster than designed. This increases the wear from areas processing • Combustible dust and tear on the engine, causing overheating flammable materials, then (Class II) and risking autoignition. If allowed to continue, • Easily-ignitable fibers the following preventive (Class III) overspeed can result in mechanical failure measures should be used. causing the engine to blow apart, igniting In Class I locations, an These measures include installation must be classified as flammable materials in the area and causing a administrative procedures using the division classification flash fire or explosion. for the safe use of portable system complying with paragraphs (c), (d), (e), and (f), or mobile equipment with or using the zone classification internal combustion engines. system specified in paragraph (g), of 29 CFR 1910.307 or Control Measures to 29 CFR 1926.407. Reduce Risk • Ensure that materials and equipment are stored and used in accord with OSHA standards such as: o 29 CFR 1910.106 or 29 CFR 1926.152, Flammable liquids; o 29 CFR 1910.107, Spray finishing using flammable and combustible materials; o 29 CFR 1910.119 or 29 CFR 1926.64, Process safety management of highly hazardous chemicals; Three workers were killed and four injured in a fire resulting from a o 29 CFR 1910.178, Powered industrial trucks. runaway diesel engine. • Ensure that worksite safety programs and safe Source: U.S. Chemical Safety Board work permit systems: For a gasoline engine, overspeed is stopped by o Address internal combustion engines as turning off the ignition switch, which shuts down ignition sources; the ignition source (spark plugs) in the cylinders. o Evaluate and establish acceptable areas, This is not the case for diesel engines. Diesel boundaries, and entry routes for mobile engines do not use spark plugs; turning off the engine ignition switch does not shut down the ignition source. Stopping the fuel supply is also ineffective because the fuel is present in the intake air. The only way to prevent mechanical failure and possible explosion is to cut off the intake air supply, using systems such as automatic engine overspeed shutdown devices. Preventing Engines from Becoming Ignition Sources Workplace Evaluation • Identify areas where flammable liquids or gases are used or stored. • Evaluate where internal combustion engines are located. • Assess contractor use of internal combustion engines in flammable material areas. An idling diesel pickup truck believed to have ignited a vapor cloud from a nearby process area. Source: U.S. Chemical Safety Board 2 internal combustion engines based on • Areas, boundaries and The Process Safety Management applicable standards and recognized and acceptable routes for (PSM) standard generally accepted good engineering mobile engines, and (29 CFR 1910.119) applies to processes in facilities that have practices; applicable facility safety flammable liquids or gases on o Mark and enforce acceptable traffic routes rules. Instruct workers site in one location in a quantity through hazardous (classified) locations; to avoid driving in areas of 10,000 pounds or more. For o Account for special procedures, which might where flammable vapors covered processes, the PSM standard addresses controlling include the use of portable gas monitors, or and gases may be present, ignition sources primarily by emergency evacuation routes for vehicles. to stay on acceptable requiring employers to: • Use other preventive measures such as: routes, and to follow site • Compile written process safety information for o Installing automatic overspeed shutdown procedures for safe access working with hazardous devices on permanently-mounted engines. in areas where flammable chemicals, including o Installing intake flame arrestors and exhaust materials are being identifying areas where flammable materials are or system spark arrest systems on permanently processed. may be present, 29 CFR mounted engines. • Signs and hazards of 1910.119(d). o Installing flammable gas and vapor detectors flammable vapor and gas • Complete a process hazard in processing areas. clouds, and associated analysis that addresses the hazards of the process, o Installing shutdown systems (positive air precautions. including control of ignition shut-off for diesel or ignition kill for gasoline), • Signs and hazards of sources such as internal intake flame arrestor, exhaust system spark internal combustion combustion engines, 29 CFR 1910.119(e). arrest, or other appropriate protective engine overspeed and • Develop and implement safe systems3 for mobile internal combustion runaway. work practices, including engines. • Emergency procedures control of vehicle access to process areas, 29 CFR o Using a safe work permit system to control for flammable materials 1910.119(f)(4). mobile combustion engine access into areas emergencies, including • Develop and implement that could contain flammable vapors and response to engine written procedures (f) and training for operators (g), gases. overspeeds and runaways. maintenance personnel (j), o Using a safe work permit system to control and contractors (h), 29 CFR the use of open flames and spark-producing Standards and 1910.119(f), (g), (h), and (j). operations and equipment (e.g., welding, • Control hot work, 29 CFR Resources 1910.119(k). grinding, brazing, etc.) In addition to following Training applicable OSHA standards, employers should also Provide training to workers and contractors on refer to the American Petroleum Institute (API), the hazards in areas that contain flammable vapors and National Fire Protection Association (NFPA), and gases. The training