26.C.02 Air quality standards.
- Whenever air monitoring indicates the presence of 5 ppm or more of hydrogen sulfide, a test must be conducted in the affected underground work areas, at least at the beginning and midpoint of each shift, until the concentration of hydrogen sulfide has been less than 5 ppm for 3 consecutive days.
- Whenever hydrogen sulfide is detected in an amount exceeding 10 ppm, a continuous sampling and indicating hydrogen sulfide monitor must be used to monitor the affected work areas.
- Employees must be informed when a concentration of 10 ppm hydrogen sulfide is exceeded.
- The continuous sampling and indicating hydrogen sulfide monitor must be designed, installed, and maintained to provide a visual and aural alarm when the hydrogen sulfide concentration reaches 10 ppm to signal that additional measures might be necessary to maintain hydrogen sulfide exposure below the PEL.
- When the competent person determines, on the basis of air monitoring results or other information, that air contaminants may be present in sufficient quantities to be dangerous to life, the employer must:
- (1) Prominently post a notice at all entrances to the underground area to inform all entrants of the hazardous condition, and
- (2) Ensure that the necessary precautions are taken.
- Whenever 5% or more of the LEL for methane or other flammable gases is detected in any underground work area or in the air return, steps must be taken to increase ventilation air volume or otherwise control the gas concentration, unless operations are conducted in accordance with the potentially gassy or gassy operation requirements: such additional ventilation controls may be discontinued when gas concentrations are reduced below 5% of the LEL.
- Whenever 10% or more of the LEL for methane or other flammable gases is detected in the vicinity of welding, cutting, or other hot work, such work must be suspended until the concentration of such flammable gas is reduced to less than 10% of the LEL.
- Whenever 20% or more of the LEL for methane or other flammable gases is detected in any underground work area or in the return:
- (1) All employees, except those necessary to eliminate the hazard, must be immediately withdrawn to a safe location above ground; and
- (2) Electrical power, except for acceptable pumping and ventilation equipment, must be cut off to the area endangered by the flammable gas until the concentration of such gas is reduced to less than 20% of the LEL.
- When ventilation has been reduced to the extent that hazardous levels of methane or other flammable gas may have accumulated, all affected areas must be tested after ventilation has been restored and before any power, other than for acceptable equipment, is restored or work is resumed and must determine whether the atmosphere is within flammable limits.
- Whenever the ventilation system has been shut down with all employees out of the underground area, only competent persons authorized to test for air contaminants must be allowed underground until the ventilation has been restored and all affected areas have been tested for air contaminants and declared safe.
Knowledge Check Choose the best answer for the question.
26-7. Steps must be taken to increase ventilation air or otherwise control the gas concentration in underground work areas when methane or other flammable gas levels are _____.
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