DOD 4145.26-M  

DoD approved flooring (military specification)

The following is from:  DoD Contractor's Safety Manual for Ammunition and Explosives (DoD 4145.26M) for floors, and standards for dealing with static electricity and explosion prevention systems.

CHAPTER 6
DoD 4145.26-M, March 13, 2008
C6.4.7. Conductive Floors, Tabletops, and Footwear. Contractors shall use conductive tabletops, floors, and shoes for grounding personnel at operations involving exposed explosives with electrostatic sensitivity of 0.1 J or less, e.g., primer, initiator, detonator, igniter, tracer, and incendiary mixtures. Bonding wires or straps shall connect the tabletops and floors to the static ground system. Materials sensitive to initiation by ESD sparks include: lead styphnate, lead azide, mercury fulminate, tetrazene, diazodinitrophenol, potassium chlorate-lead styphanate mixtures, some igniter compositions, grade B magnesium powder, and exposed layers of black powder dust. Air and dust mixtures of ammonium picrate, tetryl, tetrytol, and solid propellants are also sensitive to initiation by ESD. Testing indicates mixtures of air with vapors from many flammable liquids (e.g., ethyl ether, ethyl alcohol, ethyl acetate, acetone, and gasoline) may ignite by ESD from the human body. Therefore, contractors shall equip areas where personnel might contact these kinds of explosives and flammable liquids with conductive floors and tabletops, except when hazard analysis indicates adequate housekeeping, dust collection, ventilation, or solvent recovery methods eliminate the ignition hazard. (Refer to Reference (u) for additional information concerning ESD test data; ESD ignition sensitivity may vary depending on variations within the process.)

C6.4.7.3. Conductive Floor and Tabletop Specifications. Conductive floors and tabletops made of or covered with non-sparking materials such as lead, conductive rubber, or conductive compositions shall meet these requirements:

C6.4.7.3.1. Provide a continuous electrical path to the static ground system and the electrical resistance shall not exceed the limits specified in subparagraph C6.4.7.5.1.

C6.4.7.3.2. Provide a reasonably smooth surface that is free from cracks.
C6.4.7.3.3. Maintain compatibility of conductive floor and tabletop materials with the energetic materials present.
C6.4.7.5. Testing Conductive Footwear, Floors, and Tabletops
C6.4.7.5.1. Test Criteria.

The maximum resistance of a body, plus the resistance of the conductive shoes, plus the resistance of the floor to the ground system shall not exceed 1,000,000 ohms total. That is, if 500,000 ohms is the maximum resistance allowed from the floor to the ground system, then 500,000 ohms is the maximum combined resistance allowed for the person’s body plus the resistance of the conductive shoes. The contractor can set the maximum resistance limits for the floor to the ground system and for the combined resistance of a person’s body plus the shoes, as long as the total resistance does not exceed 1,000,000 ohms.

C6.4.7.5.2    Minimum Resistance. To protect against electrocution, the minimum resistance of the floor to the ground system and the minimum resistance of the tabletop to the ground system shall exceed 40,000 ohms in areas with 110 volts service and 75,000 ohms in areas with 220 volts service. A ground fault interrupt circuit also meets this requirement.

C6.4.7.5.5. Test Procedure. Trained personnel shall test conductive floors and tabletops upon installation and at least annually thereafter using test equipment specifically designed for this purpose and shall keep records of all test results for at least 5 years. Testing shall proceed only when the room or area is free from exposed explosives and flammable gas mixtures. The test procedure shall measure the resistance of the floor between an electrode attached to the ground system and an electrode placed at any point on the floor or tabletop and also as measured between two electrodes placed 3 ft [1 m] apart at any points on the floor or tabletop. Make both electrode-to-electrode and electrode-to-ground system measurements at five or more locations in each room, with at least two of the test locations in heavily trafficked areas. If the resistance measurement changes appreciably with time, record the resistance at the 5-second interval. To prevent biased measurements, locate the electrodes for both the electrode-to-electrode and electrode-to-ground measurements a minimum of 3 ft [1 m] away from an earth ground or other grounded items such as a door frame, ordnance handling equipment, or any grounded item resting on a conductive floor. Only trained personnel shall operate and maintain test instruments.

NOTE: The size of the floor or tabletop may make it impractical to conduct five surface resistance (electrode-to-electrode) or resistance-to-ground measurements and still remain 3 ft [1 m] away from all grounded items. In such cases, take enough measurements to ensure adequate testing of all parts of the conductive surface and document the justification for a reduced number of electrode-to-electrode or electrode-to-ground measurements in the grounding system test plan.