PPE, arc-rated clothing and tools

Personal protective equipment is the last line of defence in the hierarchy of controls. It does not prevent an arc flash or a shock; it reduces the injury when the other controls have failed. HSE-224 Lessons 8 and 9 explain arc ratings, layered clothing systems, PPE categories, rubber insulating gloves and insulated tools and test instruments in detail. This lesson focuses on how PPE is selected, provided and used in critical facilities, where electrical rooms are hot and loud, incident energies at main switchgear are high, DC systems are common and many different crews share the same PPE stations.

PPE as part of the plan, not a substitute for it

In a data centre, the PPE decision follows from everything covered so far. If the work is done in an electrically safe work condition, the equipment is not energized and no arc flash or shock PPE is needed for the work itself, although it is needed for the steps that establish the condition: opening covers to test, testing for absence of voltage and, in some cases, operating switching devices. If energized work is justified and permitted, the PPE is selected from the arc flash and shock risk assessments. In both cases, engineering controls such as energy-reducing maintenance switching and remote operation should already have reduced the exposure as far as possible.

A common error is to treat PPE as the main control: to reason that, because the site has 40 cal/cm² (167 J/cm²) suits, any task up to that level can be done energized. That reverses the hierarchy. PPE selection comes after the decisions to eliminate, substitute and engineer out the hazard, not before.

Arc-rated clothing and PPE categories

Arc-rated clothing is tested to determine its arc rating, the incident energy at which there is a 50% probability of the onset of a second-degree burn through the fabric (the arc thermal performance value, ATPV) or of the fabric breaking open (the energy breakopen threshold, EBT). The rating is marked on the garment in cal/cm². When the incident energy analysis method is used, the arc rating of the clothing system must be at least the incident energy at the working distance shown on the label or in the study. When the PPE category method is used, the standards' tables assign a category to each task and equipment type, within stated limits of fault current and clearing time, and each category has a minimum arc rating.

In data centres, most sites use the incident energy method, because they have arc flash studies and because the category tables have limits on fault current and clearing time that large data centre systems often exceed. The label tells the worker the incident energy at the working distance, and the worker selects clothing with an arc rating at least that high. Where a site uses a few standard clothing systems, for example daily-wear clothing rated around 8 to 12 cal/cm² and a 40 cal/cm² suit for higher energies, the program should say clearly which system covers which range.

Daily-wear arc-rated clothing

Many critical facilities require their electricians and critical environment technicians to wear arc-rated clothing as their normal work uniform, typically shirts and pants or coveralls rated around 8 cal/cm² or more. Daily wear has several advantages: the worker is already protected when an unexpected task arises, such as an alarm that needs investigating, and the worker does not have to change into separate clothing for low-energy tasks. It does not replace the higher-rated suits needed for higher incident energies, and it must be worn correctly: sleeves down, shirts tucked in or coveralls closed, with no meltable fabrics such as polyester or nylon worn underneath.

Heat, noise and communication

Arc flash suits and hoods are hot. Electrical rooms in data centres are often warm, and UPS rooms, generator enclosures and the hot side of busway runs can be hotter still, as HSE-320 Lesson 6 described. A worker in a 40 cal/cm² suit in a warm room can develop heat stress quickly. HSE-243, Heat and Cold Stress, explains how to assess and control it. In critical facilities, practical controls include planning heavy-PPE tasks for the coolest part of the night, keeping tasks in full suits short, providing cooling vests compatible with arc-rated clothing, and planning work and rest periods.

Hoods also reduce vision and hearing. Arc flash hood windows are tinted and can limit peripheral vision, and the hood muffles speech. Combined with the noise of transformers, cooling fans and UPS systems, this makes the three-way communication that switching requires (Lesson 8) harder. Sites address this with good lighting, hoods with ventilation fans and clear windows rated for the task, hearing protection that fits under the hood and, in some cases, communication headsets designed for use with arc-rated PPE.

Shock protection: gloves and other equipment

Shock protective equipment protects against contact with energized parts. The most important item is the rubber insulating glove, worn with leather protectors over it to protect the rubber from cuts and punctures. Gloves are classified by the maximum voltage they are designed for, and they must be selected for the voltage of the equipment.

Gloves must be air-tested and visually inspected before each use, and they must be electrically tested at regular intervals: before first issue and at least every six months afterwards, with gloves that have been tested but not issued for 12 months needing to be retested before use. The test date must be marked on or traceable to the gloves. In a data centre with shared PPE stations, gloves are a common weak point: a pair left in a station may be past its test date, may be the wrong class for the equipment, or may have been damaged by the previous user. Many sites issue gloves to individuals and track test dates centrally.

Other shock protective equipment includes insulating blankets and covers for nearby energized parts, insulated mats, and insulated and insulating tools. Insulated hand tools for live work are made and tested to recognized standards, commonly rated for 1,000 V AC and 1,500 V DC, and are marked accordingly.

from datetime import date

# Illustrative glove selection and test-date check (ASTM D120 maximum use voltages).
CLASSES = [("00", 500, 750), ("0", 1000, 1500), ("1", 7500, 11250),
           ("2", 17000, 25500), ("3", 26500, 39750), ("4", 36000, 54000)]

def glove_class(volts, dc=False):
    for name, ac_max, dc_max in CLASSES:
        if volts <= (dc_max if dc else ac_max):
            return name
    return None

def test_ok(last_test, today, issued=True):
    days = (today - last_test).days
    return days <= (183 if issued else 365)

TODAY = date(2026, 10, 1)
tasks = [("RPP branch breaker, 208 V", 208, False), ("Busway tap-off, 415 V", 415, False),
         ("Switchboard, 600 V", 600, False), ("Switchboard, 480 V", 480, False),
         ("UPS battery string, 545 V DC", 545, True), ("MV switchgear, 13.8 kV", 13800, False)]
for name, v, dc in tasks:
    print(f"{name:30s} -> class {glove_class(v, dc)} gloves or higher")

pairs = {"Station 2 pair A": date(2026, 2, 20), "Dana's issued pair": date(2026, 6, 15)}
for pair, tested in pairs.items():
    print(f"{pair:20s} tested {tested}: {'in date' if test_ok(tested, TODAY) else 'OUT OF DATE - do not use'}")

RPP branch breaker, 208 V      -> class 00 gloves or higher
Busway tap-off, 415 V          -> class 00 gloves or higher
Switchboard, 600 V             -> class 0 gloves or higher
Switchboard, 480 V             -> class 00 gloves or higher
UPS battery string, 545 V DC   -> class 00 gloves or higher
MV switchgear, 13.8 kV         -> class 2 gloves or higher
Station 2 pair A     tested 2026-02-20: OUT OF DATE - do not use
Dana's issued pair   tested 2026-06-15: in date

The program shows that class 00 gloves are the minimum for the branch circuits, the busway and the battery string's DC voltage, while the switchboards need class 0, so many sites simply issue class 0 gloves for all low-voltage work. Medium-voltage switchgear needs class 2 gloves or higher, and specialist procedures. It also catches a pair in a shared station whose last test was more than six months ago.

Test instruments

Test instruments used in data centres must be rated for the voltage and the measurement category of the circuit. Measurement categories describe the transient overvoltages an instrument can withstand: CAT III covers distribution-level equipment such as switchboards, panelboards and busway, and CAT IV covers the origin of the installation, such as the service entrance and utility connections. A meter used on main switchgear should be rated at least CAT III 1,000 V, and many sites standardize on CAT IV 600 V or higher ratings for work near the service. For DC systems the meter must also be rated for DC at the system voltage. Probes, leads and clips must carry ratings at least as high as the meter's, with finger guards and minimal exposed metal.

HSE-224 Lesson 9 covers meter features and inspection. In a critical facility, two additional points matter. First, because absence-of-voltage testing must be done live-dead-live, the site needs a reliable known source near each work location, such as a proving unit carried with the meter. Second, because AI facilities may introduce higher DC voltages, the meter fleet must be checked against any new system before work begins on it.

PPE stations and shared equipment

Most data centres keep PPE at stations near electrical rooms: arc flash suits and hoods in several sizes, face shields, gloves and protectors, insulated tools, meters and proving units, insulating blankets, barricade tape and signs. Shared PPE needs a system to keep it usable.

• Inspect suits and hoods for contamination, damage and window scratches; launder according to the manufacturer.
• Track glove test dates and remove out-of-date gloves.
• Store PPE clean, dry and out of direct sunlight, with hoods hung so windows are not scratched.
• Keep a range of sizes, because ill-fitting suits restrict movement and gaps reduce protection.
• Provide hygienic hood liners or individually issued balaclavas.
• Inventory the station regularly, and after every major maintenance window.

Contractors bring their own PPE in many cases. The host's program should say whether contractor PPE is acceptable, how it is checked and what happens when it does not meet the site's requirements, for example if a contractor's suit is rated lower than the label at the equipment they are to work on.

Other PPE in electrical spaces

Electrical work in data centres also calls for non-conductive hard hats, safety glasses or goggles under face shields and hoods, hearing protection, safety footwear with electrical hazard ratings where the site requires them, and fall protection when working at height on busway or cable tray. Ladders used near energized equipment must be non-conductive, such as fibreglass, and kept clean and dry. Battery work requires additional PPE for chemical hazards, which HSE-322 covers.