by Ellis Brasch
Remember the toy called a Jack-in-the-box? Basically, Jack was just a spring stuck in a small tin box that had a hinged lid for a top and a hand crank on the side. To get the toy to work, you pressed Jack into the box, closed the lid, secured it with a latch, and then turned a crank. At some point, Jack popped out of the box, delighting generations of youngsters. But this simple toy offers a lesson that many workers ignore. It's all about energy.
When you push Jack into the box and close the lid, you compress the spring and your effort is stored as potential energy in the spring. Potential energy is energy just waiting to do something – think of it as motion waiting to happen. When you release potential energy, something will move. That movement is kinetic energy. When the lid unlatches, it is kinetic energy that pops Jack out of the box.
Energy exists in many forms, all of which are associated with motion - and it is motion that makes energy hazardous.
Now imagine huge amounts of potential energy stored in industrial equipment that could start or move unexpectedly, just like a Jack-in-the-box – room-size ovens, mixers, vehicle lifts, compactors, and robotic arms, for example. Most accidents that involve energy happen when workers release that energy on themselves or another unsuspecting co-worker. Why? Many workers do not follow – or are not aware of – four critical steps that are necessary to keep energy from becoming deadly:
Energy exists in many forms, all of which are associated with motion – and it is motion that makes energy hazardous. Energy can harm you in different ways depending on its form. The first step in controlling hazardous energy is to know the forms of energy that power the equipment you use and how that energy can harm you if you do not properly control it. Typical energy forms include:
Most accidents that involve energy happen when workers release that energy on themselves or another unsuspecting coworker - typically during service or maintenance work.
A recent accident: A worker reached into a 6-inch by 3-inch inspection hole on a mixing machine with his left hand to clean an auger. In the meantime, a co-worker pressed a switch on a nearby control panel that he thought turned on a conveyer, but it turned on the auger, and the worker who was cleaning it lost his left arm. Neither worker had been trained to recognize the machine's hazardous energy sources, the forms and magnitude of the energy used in the workplace, or the methods necessary to control them.
The most effective way to isolate energy is with an energy isolating device – a technical name for mechanisms such as manually operated circuit breakers, disconnect switches, line valves, and safety blocks that ensure the equipment will not move or become energized. But these are effective only if you know that no one will interfere with them while you are working on the equipment. There are only two ways to be certain: They are called lockout and tagout.
Lockout is a procedure for physically securing an energy-isolating device in a safe position – typically with a lock that has a unique key. Tagout is a procedure for securing a warning sign to an energy-isolating device when a lockout device cannot be used. (Tagout requires an additional step to ensure the same protection that a lock provides.)
A recent accident: A mechanic pressed a push-button switch to de-energize a large computer-controlled machine, but did not use a power disconnect switch (the energy isolating device) as required by his company. The push-button switch stopped the machine, but did not isolate the energy – the machine started unexpectedly and crushed the mechanic's legs.
Remember the compressed spring in the Jack-in-the box? There could still be potential energy to account for after you have isolated energy from the equipment. Capacitors, coiled springs, elevated machine parts, rotating flywheels – and air, gas, steam, chemical, and hydraulic systems – are all sources of potential energy. Common ways to relieve potential energy:
A recent accident: Two workers were repairing equipment that had electrical, hydraulic, and thermal energy sources. The workers isolated and locked out the electrical and hydraulic energy but did not close a valve that blocked the thermal energy (pressurized steam). As they worked on the equipment, the pressurized steam shot through an eight-inch pipe and severely burned one of the workers across his face, arms, legs, and stomach.
Double check to ensure that the equipment is completely isolated from its energy source, that the appropriate energy isolating devices are locked or tagged, and that any potential energy has been removed.
A recent accident: A worker walking by a plywood stacking machine noticed that the machine had stopped and a plywood panel was out of place. When he tried to reposition it he triggered an electric eye that started the machine, which pinned him and severely injured him. He said he was trying to help a coworker, but he did not know how the electric eye controlled the machine.
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