concussion. Sometimes the pressure wave throws the victim away from the arc-blast. While this may reduce further exposure to the thermal energy, serious physical injury may result. The pressure wave can propel large objects over great distances. In some cases, the pressure wave has enough force to snap off the heads of steel bolts and knock over walls.
(3) A high-voltage arc can also cause many of the copper and alumi- num components in electrical equipment to melt. These droplets of molten metal can be blasted great distances by the pressure wave. Although these droplets harden rapidly, they can still be hot enough to cause serious burns or cause ordinary clothing to catch fire, even if you are 10 feet or more away.
F ive technicians were performing preventive maintenance on the electrical system of a railroad main- tenance facility. One of the technicians was assigned to clean the lower compartment of an electri- cal cabinet using cleaning fluid in an aerosol can. But, he began to clean the upper compartment as well. The upper compartment was filled with live circuitry. When the cleaning spray contacted the live circuitr , a conductive path for the current was created. The current passed through the stream of fluid, into the technician s arm, and across his chest. The current caused a loud explosion. Co-workers found the victim with his clothes on fire. One worker put out the fire with an extinguishe , and another pulled the victim away from the compartment with a plastic vacuum cleaner hose. The paramedics responded in 5 minutes. Although the victim survived the shock, he died 24 hours later of burns.
This death could have been prevented if the following precautions had been taken:
Before doing any electrical work, de-energize all circuits and equipment, perform lock-out/tag-out, and test circuits and equipment to make sure they are de-energized.
The company should have trained the workers to perform their jobs safely.
Proper personal protective equipment (PPE) should always be used.
Never use aerosol spray cans around high-voltage equipment.
Thermal burns may result if an explosion occurs when electrici- ty ignites an explosive mixture of material in the air. This igni- tion can result from the buildup of combustible vapors, gases, or dusts. Occupational Safety and Health Administration (OSHA) standards, National Fire Protection Association (NFPA) stan- dards, and other safety standards give precise safety require- ments for the operation of electrical systems and equipment in such dangerous areas. Ignition can also be caused by overheated conductors or equipment, or by normal arcing at switch contacts or in circuit breakers.
❚ OSHA—Occupational Safety and Health Administration—the Federal agency in the U.S. Department of Labor that establishes and enforces workplace safety and health regulations