In this module
Objectives covered: LO 1.7.1. By the end you will be able to:
- Describe electric shock, arc flash and arc blast.
- Explain why PPE comes after de-energising and lockout.
- Choose the correct class of rubber insulating gloves.
- Inspect and test electrical PPE, and select arc-rated clothing.
7.1 Electrical hazards
- Electric shock: current passes through the body. Around 1 mA can be felt; 10 to 20 mA can stop a person letting go; 50 to 100 mA through the chest can stop the heart.
- Arc flash: a short circuit through air releases intense heat and light. It can cause severe burns several metres away.
- Arc blast: the pressure wave from an arc can throw a person, rupture eardrums and spray molten copper.
7.2 De-energise first
The best protection is to work on equipment that is dead. Follow lockout/tagout (OSHA 1910.147 and 1910.333): isolate, lock, tag, test for absence of voltage, and earth where required. Live work should happen only when de-energising is not possible or creates a greater hazard, and only under a written energised work permit. Electrical PPE protects you during switching, testing and justified live work, and in case the system is not as dead as you thought.
7.3 Rubber insulating gloves
OSHA 1910.137 and ASTM D120 set the requirements. Gloves are rated by class:
| Class | Label colour | Maximum use voltage (AC) | Typical use |
|---|---|---|---|
| 00 | Beige | 500 V | Low-voltage control panels |
| 0 | Red | 1,000 V | 400/230 V factory distribution boards |
| 1 | White | 7,500 V | Up to 6.6 kV systems |
| 2 | Yellow | 17,000 V | 11 kV distribution |
| 3 | Green | 26,500 V | Higher distribution voltages |
| 4 | Orange | 36,000 V | 33 kV systems |
- Always wear leather protector gloves over rubber gloves to protect them from cuts and punctures.
- Do an air test before each use: roll the cuff to trap air, squeeze, and look and listen for leaks. Check for cuts, holes, swelling, ozone cracks and embedded objects.
- Rubber gloves must be electrically retested every 6 months; sleeves and blankets every 12 months (1910.137, Table I-6). Write the test date on the glove or keep a register.
- Store gloves flat in a bag, away from sunlight, heat, oil and sharp tools. Never fold them.
7.4 Other electrical PPE and tools
- Insulating sleeves, blankets and mats.
- Insulated hand tools (marked 1000 V, IEC 60900) and hot sticks for switching.
- Class E helmet (Module 6) and EH-rated safety footwear.
- A voltage detector rated for the system, tested on a known live source before and after use.
7.5 Arc-rated clothing
NFPA 70E (USA) and IEC 61482 (international) cover arc-flash protection. Arc-rated (AR) clothing has an arc rating in cal/cm², the heat it can block before a second-degree burn is likely. The rating must be equal to or higher than the incident energy calculated for the equipment. NFPA 70E also gives PPE categories when the table method is used:
| PPE category | Minimum arc rating | Typical clothing |
|---|---|---|
| 1 | 4 cal/cm² | AR shirt and trousers or AR coverall, AR face shield |
| 2 | 8 cal/cm² | AR shirt and trousers or coverall, AR face shield and balaclava, or arc flash hood |
| 3 | 25 cal/cm² | AR flash suit and hood, AR gloves |
| 4 | 40 cal/cm² | AR flash suit and hood, AR gloves |
Polyester and nylon melt onto the skin in an arc flash. Under AR clothing, wear only cotton or other non-melting fabrics.
At a 33/11 kV distribution substation, a technician racking out an 11 kV breaker wears Class 2 rubber gloves with leather protectors, an arc flash suit rated above the calculated incident energy, a Class E helmet and EH boots, and works under a switching permit. In a garment factory's 415 V LT panel room, electricians use Class 0 gloves, 1000 V insulated tools and an 8 cal/cm² AR coverall with face shield, and lock out the main breaker before work. Both sites keep a glove test register.
Learning Check
Answer these two questions to check your understanding. You can try again as many times as you like.