Uncontrolled Hazardous Energy Case Studies

Workers may be exposed to hazardous energy in several forms and combinations during installation, maintenance, service, or repair work. A comprehensive hazardous energy control program should address all forms of hazardous energy:
  • Kinetic (mechanical) energy in the moving parts of mechanical systems.
  • Potential energy stored in pressure vessels, gas tanks, hydraulic or pneumatic systems, and springs (potential energy can be released as hazardous kinetic energy).
  • Electrical energy from generated electrical power, static sources, or electrical storage devices (such as batteries or capacitors).
  • Thermal energy (high or low temperature) resulting from mechanical work, radiation, chemical reaction, or electrical resistance.

Case Studies

Between 1982 and 1997, The National Institute for Occupational Safety and Health (NIOSH) investigated 152 fatal incidents in which workers contacted uncontrolled hazardous energy. The following case reports summarize five of these investigations.
1. Uncontrolled Kinetic Energy
A 25-year-old male worker at a concrete pipe manufacturing facility died from injuries he received while cleaning a ribbon-type concrete mixer. The victim's daily tasks included cleaning out the concrete mixer at the end of the shift. The clean-out procedure was to shut off the power at the breaker panel (approximately 35 feet from the mixer), push the toggle switch by the mixer to make sure that the power was off, and then enter the mixer to clean it.

No one witnessed the event, but investigators concluded that the mixer operator had shut off the main breaker and then made a telephone call instead of following the normal procedure for checking the mixer before anyone entered it. The victim did not know that the operator had de-energized the mixer at the breaker. Thinking he was turning the mixer off, he activated the breaker switch and energized the mixer. The victim then entered the mixer and began cleaning without first pushing the toggle switch to make sure that the equipment was deenergized. The mixer operator returned from making his telephone call and pushed the toggle switch to check that the mixer was deenergized. The mixer started, and the operator heard the victim scream. He went immediately to the main breaker panel and shut off the mixer.

Within 30 minutes, the emergency medical service (EMS) transported the victim to a local hospital and then to a local trauma center. He died approximately 4 hours later [NIOSH 1995].
2. Uncontrolled Electrical Energy
A 53-year-old journeyman wireman was electrocuted when he contacted two energized, 6.9-kilovolt buss terminals. The victim and two coworkers (all contract employees) were installing electrical components of a sulfur dioxide emission control system in a 14-compartment switch house.

The circuit breaker protecting the internal buss (a conducting bar, rod, or tube that carries heavy currents to supply several electric circuits) within the switch house had been tripped out and marked with a tag — but it had not been secured by locking. This procedure was consistent with the hazardous energy control procedures of the power plant.

The victim and his coworkers were wiping down the individual compartments before a pre-startup inspection by power plant personnel. Without the knowledge of the victim and his coworkers, power plant personnel had energized the internal buss in the switch house. When the victim began to wipe down one of the compartments at the south end of the switch house, he contacted the A-phase buss terminal with his right hand and the C-phase buss terminal with his left hand. This act completed a path between phases, and the victim was electrocuted.
A coworker walking past the victim during the incident was blown backward by the arcing and received first-degree flash burns on his face and neck. A second coworker at the north end of the switch house heard the explosion and came to help. He notified the contractor's safety coordinator by radio and requested EMS. The EMS responded in about 15 minutes and transported the victim to a local hospital emergency room where he was pronounced dead [NIOSH 1994].
3. Uncontrolled Kinetic Energy
A 38-year-old worker at a county sanitary landfill died after falling into a large trash compactor used to bale cardboard for recycling. The cardboard was lifted 20 feet by a belt conveyor and fed through a 20- by 44-inch opening into a hopper. The hopper had automatic controls that activated the baler when enough material collected in the baling chamber. When the baler was activated, material in the chamber was compressed by a ram that entered the chamber from the side. Excess material above the chamber was trimmed by a shearer.

On the day of the incident, cardboard jammed at the conveyor discharge opening. Without stopping, deenergizing, or locking out the equipment, the victim rode the conveyor up to the discharge opening to clear the jam. He fell into the hopper and the baling cycle was automatically activated, amputating his legs. The victim bled to death before he could be removed from the machine [Colorado Department of Public Health and Environment 1994].
4. Uncontrolled Potential Energy
The 32-year-old owner of a heavy equipment maintenance business died after a wheel and tire assembly exploded during repair work. The victim was removing the assembly from a test roller when it exploded and struck him with the flying split rim of the wheel.

The test roller was a large, two-wheeled cart that carried about 60,000 pounds of concrete weights. The roller was used in highway construction to test road surfaces for proper compaction.

The victim had been working as a subcontractor to repair the wheel and tire assembly, which had been smoking earlier in the day and was believed to be rubbing against the concrete weights. The assembly consisted of a two-piece outside rim and an inside ring retainer that was held together and mounted on the axle by 20 wheel bolts and nuts. Normal air pressure for the mounted tire was 70 psi.

The victim raised and blocked the roller. Without discharging the air from the tire and using no personal protective equipment, he began to remove the wheel nuts using a pneumatic impact wrench. He had no training or experience with this type of work or in the servicing of this type of wheel. He did not realize that only some of the bolts held the wheel tire assembly to the axle. The remainder held the outer half of the rim to the inside half, securing the tire to the wheel. As the victim removed the nineteenth wheel nut, the pressurized air in the tire discharged explosively, causing the split rim to fly off the wheel and strike him. He died from cerebral contusions and lacerations [Minnesota Department of Health 1992].
5. Uncontrolled Kinetic and Thermal Energy
A 33-year-old janitorial worker died after he was trapped inside a linen dryer at a hospital laundry while cleaning plastic debris from the inside of the dryer drum. The cleaning task (which usually took 15 minutes to an hour) involved propping open the door to the dryer with a piece of wood and entering the 4- by 8-foot dryer drum. The melted debris was removed by scraping and chiseling it with screwdrivers and chisels. The dryer was part of an automated system that delivered wet laundry from the washer through an overhead conveyor to the dryer, where it was dried during a 6-minute cycle with air temperatures of 217° to 230° F. The system control panel was equipped with an error light that was activated if the dryer door was open, indicating that the dryer was out of service.

On the night of the incident, the victim propped the door open and entered the dryer drum without deenergizing or locking out the dryer. He began to clean the inside of the drum. Although the error light had been activated when the door was propped open, the signal was misinterpreted by a coworker, who restarted the system. When the system was restarted, the overhead conveyor delivered a 200-pound load of wet laundryto the dryer — knocking out the wooden door prop, trapping the victim inside, and automatically starting the drying cycle. The victim remained trapped inside until the cycle was completed and was discovered when the load was discharged from the dryer. He died thirty minutes later of severe burns and blunt head trauma [Massachusetts Department of Public Health 1992].


Review of the NIOSH data indicates that three related factors contribute to injuries and deaths that occur when workers perform installation, maintenance, service, or repair work near hazardous energy sources:
  • Failure to completely deenergize, isolate, block, and/or dissipate the hazardous energy source.
  • Failure to lockout and tagout energy control devices and isolation points after the hazardous energy source has been deenergized.
  • Failure to verify that the hazardous energy source was deenergized before beginning work.
These fatalities could have been prevented if comprehensive hazardous energy control procedures had been implemented and followed.

NIOSH recommends that employers implement the following steps to prevent injuries and deaths of workers who must work with hazardous energy in their jobs:
  1. Comply with OSHA regulations.
  2. Develop and implement a hazardous energy control program.
  3. Identify and label all hazardous energy sources.
  4. Deenergize, isolate, block, and/or dissipate all forms of hazardous energy before work begins.
  5. Establish lockout/tagout programs that:
    • Require workers to secure energy control devices with their own individually assigned locks and keys — only one key for each lock the worker controls (Use of master keys should be reserved for unusual circumstances when the worker is absent from the workplace. However, if master keys are necessary, keep them under supervisory control. List the proper procedures for using them in the written program for controlling hazardous energy.);
    • Require that each lock used to secure an energy control device be clearly labeled with durable tags to identify the worker assigned to the lock;
    • Make sure that the worker who installs a lock is the one who removes it after all work has been completed; and
    • If work is not completed when the shift changes, workers arriving on shift should apply their locks before departing workers remove their locks.
  6. Verify by test and/or observation that all energy sources are deenergized before work begins.
  7. Inspect repair work before reactivating the equipment.
  8. Make sure that all workers are clear of danger points before reenergizing the system.
  9. Train all workers in the basic concepts of hazardous energy control.
  10. Include a hazardous energy control program with any confined space entry program.
  11. Encourage manufacturers to design machines and systems that make it easy to control hazardous energy.

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