Under 29 CFR 1910.134, when is a supplied-air respirator (SAR) required rather than an air-purifying respirator (APR) during boiler NDT work?
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A
When oxygen-deficient atmospheres or IDLH concentrations are present
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B
Whenever entering any boiler shell
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C
When ambient temperature exceeds 90°F
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D
When performing ultrasonic testing only