Arc-rated and shock protective PPE

Personal protective equipment is the last line of defence, but for justified energized work and for the steps of establishing an electrically safe work condition, it is essential. Electrical PPE falls into two families that protect against different hazards: arc-rated equipment, which limits burn injury from an arc flash, and shock protective equipment, such as rubber insulating gloves, which prevents current from flowing through the body. This lesson explains how each is rated, how to select it and how to inspect and care for it.

Arc ratings: ATPV and EBT

Arc-rated clothing and equipment are tested by exposing fabric panels to real electric arcs and measuring the heat that passes through. The result is the arc rating, expressed in cal/cm². It is the lower of two values:

• The arc thermal performance value (ATPV) is the incident energy at which there is a 50 % probability that enough heat will pass through the fabric to cause the onset of a second-degree burn.
• The energy of breakopen threshold (EBT) is the incident energy at which there is a 50 % probability that the fabric will break open, creating holes that let heat through.

The arc rating is the value printed on the garment label. Fabric is tested to ASTM F1959, garments are specified by ASTM F1506 for flame-resistant and arc-rated textile materials, face protection by ASTM F2178, gloves by ASTM F2675 and rainwear by ASTM F1891. CSA Z462 references these ASTM standards and IEC 61482 for equipment tested to international methods. Clothing labelled only as flame-resistant (FR), for example to CAN/CGSB-155.20 for hydrocarbon flash fire, is not necessarily arc-rated; look for an arc rating in cal/cm².

Layered systems

Arc-rated garments can be worn in layers, for example an arc-rated shirt under an arc-rated jacket, or an arc flash suit over an arc-rated shirt and trousers. The protection of the layered system is not the sum of the individual ratings; it must be determined by testing the combination. Manufacturers publish tested ratings for their layered systems. In general, layering increases protection because the air gap between layers adds insulation, but the only valid number is the tested system rating.

Everyday clothing worn under arc-rated clothing must be made of non-melting natural fibres, such as untreated cotton, wool, rayon or silk, or blends of them, or be arc-rated itself. Meltable fibres such as polyester, nylon, acrylic and polypropylene are not permitted next to the skin inside the arc flash boundary, except in small amounts that the employer has assessed, such as elastic in socks and underwear. Arc-rated garments must be the outermost layer, except for outer layers of arc-rated rainwear or other garments rated at least as high.

PPE categories

When the PPE category method is used (Lesson 5), each category specifies a set of equipment. When the incident energy method is used, the employer selects equipment with an arc rating at least equal to the incident energy, and the categories are a convenient reference. The table summarizes the typical equipment.

Face protection deserves particular attention. Burns to the face and head are among the most disfiguring arc flash injuries, and the face is usually the part of the body closest to the arc. A face shield must be arc-rated, must wrap around to protect the sides of the face, and must be combined with a balaclava or hood where the category requires it. Safety glasses or goggles are worn underneath, because shields can be knocked off by the blast. Hearing protection, typically ear canal inserts, is required inside the arc flash boundary.

Hand protection for arc flash can be heavy-duty leather gloves, arc-rated gloves or rubber insulating gloves with leather protectors. Rubber insulating gloves with leather protectors provide both shock and arc flash protection and are often the best choice whenever shock is also a hazard. Leather protectors have shown good arc flash performance in testing, but the gloves must not be worn without them.

Rubber insulating gloves

Rubber insulating gloves are the main shock protective equipment for hands and are made to ASTM D120 (and the equivalent IEC 60903). They are classified by maximum use voltage, which is the highest voltage at which the glove may be used, and each class has a coloured label on the cuff.

Inspecting and caring for gloves

Gloves must be inspected visually and air tested before each day's use and immediately after any incident that may have damaged them. The air test traps air inside the glove by rolling the cuff, then squeezes it to inflate the fingers and palm while the worker looks, listens and feels for leaks. The visual inspection looks for cuts, punctures, tears, ozone cracking, embedded objects, swelling, softening, hardening, stickiness and changes in texture. A glove that fails any check is removed from service immediately.

Rubber insulating gloves must also be electrically retested by a qualified test laboratory before first issue and at regular intervals. The common interval, used in CSA Z462 by reference to ASTM F496 and in many provincial rules, is every six months for gloves. Ontario construction rules (O. Reg. 213/91 s. 193) require gloves rated above 5,000 V AC to be tested every three months while in service and every six months when not. Gloves that have not been issued for twelve months must be retested before use. The test date is stamped on the cuff.

Leather protectors must be worn over rubber insulating gloves, to protect the rubber from cuts and punctures. Protectors must be shorter than the rubber gloves, leaving a minimum clearance between the protector cuff and the rubber glove cuff that increases with class: about 13 mm (½ in) for classes 00 and 0, 25 mm (1 in) for class 1, 51 mm (2 in) for class 2, 76 mm (3 in) for class 3 and 102 mm (4 in) for class 4. Gloves should be stored in a protective bag, cuff down, away from sunlight, heat, ozone sources and sharp objects, and never folded or turned inside out.

Other shock protective equipment

Other voltage-rated equipment includes rubber insulating sleeves for arm protection when reaching inside the restricted approach boundary, insulating blankets and line hose to cover energized parts, insulating mats, dielectric footwear (which is a supplementary protection, not a primary one) and insulated barriers. Each has its own ASTM standard and retest interval. Dielectric overshoes and insulating mats help, but the primary protection is always to avoid contact and to insulate the hands.

Care and maintenance of arc-rated clothing

Arc-rated clothing only performs as rated if it is cared for properly. It must be inspected before each use and removed from service if it is torn, has holes, is heavily soiled with flammable materials such as oil or grease, or has been repaired with non-arc-rated thread or patches. Flammable contaminants can ignite and continue burning even on arc-rated fabric. Laundering should follow the manufacturer's instructions; bleach, fabric softeners and starch can reduce the protection of some fabrics. Garments that have been exposed to an arc flash must be removed from service, even if they look intact.

Fit matters as well. Garments that are too tight compress the air gap that helps insulate the skin, while garments that are too loose can catch on equipment. Sleeves should be fastened at the wrist, shirts tucked in or covered by a coverall, and collars closed. Hoods and face shields must be compatible with the hard hat and safety glasses and must not fog in a way that tempts the worker to lift them. Employers who want arc-rated clothing worn consistently choose comfortable, well-fitting daily uniforms rated at least 8 cal/cm², so that the protection is already on when an unexpected task arises.