Troubleshooting can introduce many new safety concerns especially when inspecting equipment that is energized. Testing often requires the troubleshooter to temporarily connect test instruments to live terminals which may involve opening enclosures or cabinets that normally are locked or bolted closed to protect workers.
This introduces two main hazards:
1. Shock Hazard: If you were to contact live equipment with your body or a tool you are holding the current flowing through your body could cause severe injury, burns, and even death.
2. Flash Hazard: If you are in the vicinity of equipment that fails and causes an electric arc, the flash, heat and shrapnel caused by the arc can also be life threatening.
Electricity travels in closed circuits, normally through a conductor, but sometimes a person’s body an efficient
conductor of electricity mistakenly becomes part of the electric circuit. This can cause an electrical shock.
Shocks occur when a person’s body completes the current path with:
• both wires of an electric circuit;
• one wire of an energized circuit and the ground;
• A metal part that accidentally becomes energized due, for example, to a break in its insulation.
When a person receives a shock, electricity flows between parts of the body or through the body to a ground or the earth.
What effect do shocks have on the body?
An electric shock can result in anything from a slight tingling sensation to immediate cardiac arrest.
The severity depends on the following:
• the amount of current flowing through the body,
• the current’s path through the body,
• the length of time the body remains in the circuit, and
• the frequency of the current
The following table shows the general relationship between the amount of current received and the
reaction when current flows from the hand to the foot for just 1 second.
Protecting Against Shock Hazards
Electrical equipment is generally designed to minimize electrical hazards. This is normally done through:
• The use of guards and barriers,
• Grounding of equipment cases
• Use of proper insulation
• Installation of protective electrical devices
However, the hazards cannot be totally eliminated. You may have to replace equipment, open an enclosure or even perform tests on live equipment.
In order to protect you from these hazards, safe work practices have been developed. Some examples are:
• de-energizing electric equipment before inspection or repair,
• keeping electric tools properly maintained,
• exercising caution when working near energized lines And Using appropriate protective equipment.
Following safe work practices is an important way that you can protect yourself from electrical hazards.
One work practice that is extremely important to the trouble-shooter because of the testing and repair work performed is Lockout/Tag out. Proper lockout/tag out procedures protect you from the dangers of the accidental or unexpected start-up of electrical equipment and are required for general industry by OSHA (Occupational Safety and Health Authority) Standard .These procedures ensure that electrical equipment is de-energized before it is repaired or inspected to protect you against electrocution or shock.
The first step before beginning any inspection or repair job is to turn the current off at the switch box and padlock the switch in the OFF position. This applies even on so-called low-voltage circuits. Securely tagging the switch or controls of the machine or equipment being locked out of service clarifies to everyone in the area which equipment or circuits are being inspected or repaired. Only qualified electricians who have been trained in safe lockout procedures should maintain electrical equipment. No two of the locks used should match, and each key should fit just one lock. In addition, one individual lock and key should be issued to each maintenance worked authorized to lock out and tag the equipment. All employees who repair a given piece of equipment should lock out its switch with an individual lock. Only authorized workers should be permitted to remove it.
2. Flash Hazards
If you are familiar with electric arc welding, then you are aware that the small arc created by the welding equipment can generate enough heat to melt metal as well as generate enough UV rays to burn your skin.
In the case when electrical equipment fails causing an electrical arc, the energy released during the arcing
can be many, many times greater than the welding arc and can cause severe flash burns. The burns fall into one of three categories:
• First Degree: the outer skin layer is damaged, it is painful, but since the growth areas are not
damaged, the skin is quickly regrown and no scarring is left.
• Second Degree: the outer skin layer is severely damaged and blistering usually occurs. Healing is much longer as it occurs from the deeper sweat glands and hair follicle areas. Scarring is often the result.
• Third Degree: complete destruction of the skin and growth areas. If the burn is small healing may occur from the sides, however skin grafting is usually required.
Protecting Against Flash Hazards
Hard hats, safety glasses, gloves and work boots with electrical insulation rating give the worker protection during normal work, however in the event of circuit or switchgear failure resulting in a thermal arc being created, much greater protection is required.
The following is some general information on protecting against flash hazards. Be sure to review the appropriate legislation and your company policies before attempting to work near live electrical apparatus.
Flash Protection Clothing
Clothing can be made from many different materials. These materials have an Arc Thermal Performance Exposure Value (ATPV) associated with them which is defined as the amount of heat energy that the fabric will handle deflect or absorb. Some of these materials offer better protection against the heat caused from an arc than others.
For normal work clear lenses are adequate, however for flash protection like that required for live work, troubleshooting, switching and applying or removing grounds, then flash rated eye protection is required. In some cases full face protection is required.
Other PPE (Personal Protection Equipment)
Other specialized personal protective equipment may be required when performing work where a flash
hazard is present. Some examples are: fire resistant hard hat liner, leather gloves, hearing protection and leather work shoes.