Conductive floors, footwear, and testing under DoD Manual 4145.26

DoD Manual 4145.26 distinguishes the combined personnel-grounding path from the resistance of a tabletop alone. It also sets minimum floor-to-ground and tabletop-to-ground resistance to protect against electrocution.

The floor and the person’s body plus shoes share a single 1,000,000-ohm resistance limit. Their individual maximums can differ, but the combined resistance must stay within that total. The DoD person-shoe-floor resistance budget explains the allocation and the manual’s example.

A ground fault interrupt circuit also meets the minimum-resistance requirement in C6.4.7.5.2.

Under C6.4.7 and C6.4.7.3, conductive floors and tabletops must connect to the static ground system through bonding wires or straps. Surfaces made of or covered with non-sparking materials, such as conductive rubber or conductive compositions, must:

• Provide a continuous electrical path to the static ground system within the resistance limits referenced in C6.4.7.5.1.
• Be reasonably smooth and free from cracks.
• Use materials compatible with the energetic materials present.

These connections do not remove the separate equipment-bonding requirement. Under C6.4.5, contact with a conductive floor or tabletop does not establish permanent-equipment bonding.

Operators must wear conductive shoes in areas requiring conductive mats, floors, or runners. Visitors must wear conductive shoes, ankle straps, or similar devices, one on each leg (C6.4.7.4).

All personnel must test conductive footwear daily before use. The body-plus-shoes result must satisfy C6.4.7.5.1, accounting for the floor’s share of the combined 1,000,000-ohm limit. Supervisors must retain documentation of all test results, including calibration of the test equipment (C6.4.7.5.4).

Personnel must not test shoes in rooms or areas containing exposed explosives or flammable gas mixtures.

Under C6.4.7.5.5, trained personnel must test conductive floors and tabletops upon installation and at least annually thereafter, using equipment specifically designed for this purpose. All test results must be retained for at least five years.

Testing may proceed only when the room or area is free from exposed explosives and flammable gas mixtures.

The DoD test procedure requires both measurements:

• Resistance between an electrode attached to the ground system and an electrode on the floor or tabletop.
• Resistance between two electrodes placed 3 ft [1 m] apart on the floor or tabletop.

Both measurements must be made at five or more locations in each room, including at least two heavily trafficked locations. Electrodes for both measurements must remain at least 3 ft [1 m] from earth ground or other grounded items, such as door frames or grounded equipment. If resistance changes appreciably with time, record the resistance at the five-second interval.

The small-surface test-location exception applies when the floor or tabletop is too small for five measurements while maintaining that clearance. The exception does not reduce the clearance from grounded items.

When a hazard remains localized, C6.4.7.2 permits conductive mats or runners instead of conductive floors throughout an entire building or room. The mats and runners must meet all specifications and test requirements that apply to conductive floors.

C6.4.7.2 permits wrist straps in place of conductive floors and shoes for personnel grounding at small scale and isolated operations when justified by hazard analysis.

DoD Manual 4145.26 prohibits sweeping compounds containing wax on conductive floors if the wax can reduce conductivity (C3.5.5).

Conductive shoes must not be worn by electricians working on electrical equipment (C3.8.5), or by personnel working on electrical equipment in conductive-floor areas (C6.4.7.4). Before electrical work begins, exposed explosives and other static-sensitive hazardous material must be removed; in conductive-floor areas, operators must remove all ammunition and explosives sensitive to electrostatic discharge.