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This article is based on a presentation by David Frazelle, divisional environmental, health, and safety manager for ADM Milling Co., Decatur, IL (217-451-4406). He spoke in May 2007 at the International Association of Operative Millers Conference and Expo in Overland Park, KS.

The numbers tell a sobering story. Every year, U.S. workplaces report an estimated 30,000 nonfatal electrical shock incidents. More than 2,000 people are admitted to burn centers with severe electrical burns. Electrical incidents kill between 600 and 1,000 people annually. More than half of those deaths involve voltages under 600 volts.

The three main hazards of electricity are:

• Electrical shock.

• Electrical arc.

• Electrical blast.

Electrical Shock

Electrical shock is caused by a difference in potential that causes a flow of electrons across the human body. The amount of electrical current flow depends on a number of factors, including type of circuit, voltage, resistance of the body, amperage, pathway through the body, and the duration of contact.

It doesn’t take a lot of amperage to cause injury or death. Table 1 shows the effects of various levels of electrical current through the body. A current as low as 25 mA can be fatal to some people. The most damaging pathways through the body pass through the lungs, heart, or brain.

Amperage can be calculated by using Ohm’s Law, which states that amperage equals volts divided by resistance.

For example, the average human body offers 1,000 ohms of resistance. Exposure to the standard U.S. voltage of 120v yields 120mA in amperage. According to the chart, that’s twice as much amperage as it takes to produce ventricular fibrillation, which is usually fatal.

Electrical Arc

An electrical arc occurs when current suddenly leaps across the air from energized equipment to a nearby ground, in this case a human body. Approximately half of serious electrical injuries involve burns from electrical arcs.

The number one way to prevent injuries from electrical arcs is to allow only trained people wearing arc protection equipment to approach energized electrical equipment. Spectators must stay away. Fatalities can occur as far as 10 feet or more from the equipment generating the arc.

The temperature of an electrical arc is 35,000 degrees F or four times hotter than the surface of the sun. (By contrast, exposure to as little as 205 degrees for a tenth of a second can cause an incurable third-degree burn.)

Electrical Arc Blast

The most dangerous effect of an electrical arc is an arc blast, which can occur when electrical equipment is exposed to arc temperatures and is vaporized. Copper wire exposed to an electrical arc instantly expands 67,000 times by volume.

Between 80% and 90% of electrical injuries can be traced to unsafe acts by employees. These include:

• Failure to de-energize electrical equipment for repair or inspection.

• Use of improper, defective, or unsafe tools.

• Use of conductive tools or equipment too close to energized parts.

• Horseplay.

Regulatory Standards

Both the Occupational Safety and Health Administration (OSHA) and the National Fire Protection Association (NFPA) have established electrical safety standards to provide practical safeguarding of employees in the workplace.

OSHA. Underlying all of OSHA’s safety standards is Section 5, the so-called “General Duty Clause,” which requires all employers to furnish employees with a workplace free from recognized hazards that could cause death or physical harm. However, OSHA standards 1910.332 through 1910.335 specifically address electrical safety in the workplace.

• Only qualified personnel may work on exposed, energized electrical equipment or circuit parts using proper procedures and personal protective equipment (PPE).

• Live parts to which an employee may be exposed must be de-energized before the employee works on or near them, unless it can be demonstrated that de-energizing introduces additional or increased hazards or is infeasible due to equipment design or operational limitations.

• If live parts are not de-energized, the employer must have a written procedure to protect employees from direct or indirect contact. This procedure must be suitable for conditions and based on the level of voltage.

• Employees working in areas where there are potential electrical hazards must be provided with and use PPE that is appropriate for the specific parts of the body to be protected and for the work to be performed.

NFPA. This association addresses electrical safety in the worklace through the NFPA 70E standard. This is a so-called “consensus standard,” created by a blue-ribbon panel of industry experts representing the best available knowledge. While it is not legally binding on industry, NFPA standards frequently are used in court cases as evidence. And NFPA standards have a way of becoming part of OSHA standards, which are legally binding.

NFPA 70E requires electrical workers to be trained in safety-related work practices and procedural requirements as necessary to provide provide protection from the electrical hazards associated with their respective job or task. They must be able to identify and understand the relationship between the hazards and injuries that could result. Qualified persons know:

• The construction of the equipment.

• The operation of the equipment.

• Work methods.

• Electrical hazards and avoidance.

• Precautionary techniques and PPE.

• Arc flash protection, insulating, shielding, and insulated tools.

• Skill and techniques necessary to distinguish exposed live parts.

• Determine nominal voltage.

• Approach distances.

• The process of determining the hazard and PPE necessary to perform the task.

Section 110.7(F) of NFPA 70E requires that a hazard and risk evaluation procedure must be performed before work begins on our near live parts operating at 50 volts or more, where an electrical hazard exists.

This includes flash hazard, which NFPA defines as any dangerous condition associated with the release of energy caused by an electric arc.

Personal Protective Equipment

OSHA and NFPA both require employers to provide appropriate PPE to electrical workers and training in how to use it.

Head. Employees working with electrical equipment must wear Class E head protection that is non-conductive up to 20,000 volts. Eye and face. Employees must wear eye and/or face protection from arcs, flashes, and flying objects.

Hand. Insulated gloves provide varying degrees of protection and are classified by color indicating maximum voltage exposure (See Table 2.) Insulating gloves must be tested electrically every six months, under the OSHA standard. In addition, they must be inspected visually for tears, rips, and punctures. A glove inflator, available from Salisbury Co., Skokie, IL (877-406-4501), can simplify visual inspection.

Clothing. Employees must wear flame-resistant clothing whenever there is possible exposure to an electric arc flash above the threshold energy level for a second-degree burn. Employees may not wear fabrics that would increase injury, including rayon, nylon, polyester, and acetate. Arc protective equipment, including electrical flash hoods and suits, must be worn wherever arc flash is a potential.

Job briefing. NFPA 70E requires that before any electrical job begins, the employee in charge must conduct a job briefing with any other employees involved. The briefing must cover such topics as hazards present, procedures, precautions, controlling energy, and required PPE. For ongoing, repetitive work, one briefing is required each shift. An additional briefing is required for any significant changes in the job.

Ground fault circuit interruptor (GFCI). A ground fault circuit interruptor is an important protective device that can prevent electrical shock when using a cord-connected piece of equipment. It operates on the differential current “hot leg” of a live circuit and a neutral ground. When it detects a hazardous condition, the GFCI pens the circuit within 25 milliseconds. Generally, it is set to operate when a leakage is over 5 mA.

Written by Ed Zdrojewski, contributing editor

Reprinted from First Quarter 2008 MILLING JOURNAL.

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