What Is Hazardous Energy?
OSHA defines an energy source as any source of electrical, mechanical, hydraulic, pneumatic, chemical, thermal, or other energy. During servicing and maintenance, any of these energy types can cause injury through unexpected energization, start-up, or release of stored energy.
Identifying every energy source on a piece of equipment is the foundation of any lockout/tagout procedure. Missing even one source can have fatal consequences.
Electrical Energy
Sources: Power supply circuits, batteries, capacitors, static charge, electromagnetic fields.
Hazards: Electrocution, arc flash, burns. Severity depends on voltage, amperage, and duration of contact.
Isolation methods: Disconnect switches, circuit breakers, removal of fuses. Capacitors must be discharged after isolation. Batteries must be disconnected.
Common in: Every industrial facility. Electrical energy is the most universal hazardous energy type, present in virtually all machinery.
Mechanical Energy
Sources: Rotating parts (flywheels, shafts, gears), reciprocating parts (pistons, rams), springs, counterweights.
Hazards: Crushing, amputation, entanglement, struck-by injuries from moving components.
Isolation methods: Mechanical energy is often controlled by disconnecting the power source that drives the motion, then waiting for components to stop. Springs must be released or blocked. Flywheels must coast to a stop (do not use the brake as a lockout method).
Common in: Presses, conveyors, machine tools, packaging equipment, any equipment with rotating or reciprocating parts.
Hydraulic Energy
Sources: Hydraulic pumps, pressurized fluid lines, accumulators, cylinders.
Hazards: High-pressure fluid injection (can penetrate skin), crushing from cylinder movement, burns from hot hydraulic fluid. Hydraulic injection injuries are medical emergencies even when the wound appears minor.
Isolation methods: Close isolation valves, bleed lines to zero pressure, block cylinders in the desired position. Accumulators must be discharged or isolated. Verify zero pressure with a gauge after bleeding.
Common in: Hydraulic presses, injection molding machines, mobile equipment (forklifts, excavators), industrial robots.
Pneumatic Energy
Sources: Compressed air supply, pressurized vessels, air cylinders, air-over-hydraulic systems.
Hazards: Unexpected cylinder movement, rupture of pressurized components, projectiles from air pressure, noise-induced hearing damage from sudden release.
Isolation methods: Close supply valves, bleed lines and cylinders to zero pressure, disconnect air supply hoses. Verify zero pressure with a gauge.
Common in: Pneumatic tools, air-operated clamps, material handling systems, painting and coating systems.
Chemical Energy
Sources: Process chemicals in lines or vessels, reactive substances, corrosive materials, flammable or combustible materials.
Hazards: Chemical burns, toxic exposure, fire, explosion, environmental release.
Isolation methods: Close line valves, drain and purge lines, install blank flanges or blinds, double-block-and-bleed configurations for toxic or high-hazard chemicals.
Common in: Chemical processing, water treatment, pharmaceutical manufacturing, food and beverage processing, refineries.
Thermal Energy
Sources: Steam lines, heated surfaces, heat exchangers, ovens, furnaces, molten materials, cryogenic systems.
Hazards: Burns from hot surfaces or fluids, scalding from steam, cold burns from cryogenic materials. Thermal energy can persist long after the heat source is isolated.
Isolation methods: Close steam valves, drain lines, allow surfaces to cool to a safe temperature. In some cases, barriers or insulation are used while waiting for cool-down. Monitor surface temperature before beginning work.
Common in: Boilers, autoclaves, heat exchangers, industrial ovens, plastics processing, food processing.
Gravitational (Potential) Energy
Sources: Elevated machine components, suspended loads, counterweights, raised platforms, material in hoppers or bins.
Hazards: Crushing from falling components, struck-by from dropped loads. Gravity is always present and does not require a power source.
Isolation methods: Lower components to the resting position, install mechanical blocks or pins, secure suspended loads with chains or stands rated for the weight. Never rely solely on hydraulic or pneumatic pressure to support a raised load during maintenance.
Common in: Overhead cranes, hoists, presses with raised rams, guillotine-style machines, vehicle lifts.
Stored and Residual Energy
After all energy sources are isolated, stored or residual energy may still be present. Per OSHA 1910.147(d)(5), all stored energy must be relieved, disconnected, restrained, or rendered safe before work begins. If reaccumulation is possible, verification must continue throughout the servicing work.
Common examples of stored energy: charged capacitors (electrical), compressed springs (mechanical), pressurized accumulators (hydraulic), air in receiver tanks (pneumatic), and elevated loads (gravitational). A complete LOTO procedure addresses each stored energy source explicitly.
Identifying Energy Sources in Your Facility
The best method for identifying hazardous energy sources is a physical walkdown of each piece of equipment with experienced maintenance personnel. Review electrical schematics, P&IDs, and equipment manuals, but do not rely on documentation alone. The walkdown often reveals energy sources that drawings do not show: a gravity hazard from an elevated component, residual pressure in a dead-end line, or a secondary power feed that was added after the original installation.
Document every energy source in the equipment's lockout/tagout procedure with its type, magnitude, location, and isolation method. LOTOBuilder's procedure builder includes a pre-configured energy type library to ensure nothing is missed. Start your free trial.
