Regulations and Standards

Are there any regulatory requirements to protect employees working in vaults and manholes?

OSHA Section CFR Part 1910.269(t)(7) for employee protection states:

"Where a cable in a manhole has one or more abnormalities that could lead to or be an indication of an impending fault, the defective cable shall be deenergized before any employee may work in the manhole, except when service load conditions and a lack of feasible alternatives require that the cable remain energized. In that case, employees may enter the manhole provided they are protected from the possible effects of a failure by shields or other devices that are capable of containing the adverse effects of a fault in the joint."

Is there a standard to provide guidance for its effectiveness and capability?

The standard ASTM 2676-09 has three parts that are scored to pass the test:

1. The KA (KiloAmps) threshold which chronicles blanket maximum current at which it will fail at 10 cycles.

2. Time in cycles it takes the blanket to fail thereby calculating the blankets mechanical strength in number called KA Cycles. This number is derived by multiplying the threshold number, for example 25KA with the cycle time, for example 20 cycles, the time the blanket held until failure, to equal the KA Cycle level of 500 which is the total energy management of 500KA.

3. Evaluate ability of the blanket to self-extinguish after the arc explosion ceases.

ASTM 2676-09 standard provides for three levels of certification: 15KA, 25KA, and 40KA.

Arc Suppression Blanket - References