The confined space should be ventilated so that levels of combustibles do not exceed what and toxic substances do not reach what?

The confined space should be ventilated so that levels of combustibles do not exceed what and toxic substances do not reach what?

• A. exceed 50% of their LEL; reach their TLV
• B. not exceed 10% of their LEL; reach their TLV
• C. exceed 10% of their LEL; not reach TLV
• D. not exceed 5% of their LEL; not reach TLV

Answer: (B)

Ventilation in confined spaces aims to control two hazards at once: flammability and toxicity. The lower explosive limit (LEL) is the gas concentration at which a mixture becomes capable of ignition; keeping combustibles well below that threshold reduces the chance of ignition if an ignition source is present. A common safety target is no more than about 10% of the LEL for combustibles. For toxic substances, the goal is to stay below the level defined by the TLV (threshold limit value), which represents a safe exposure concentration over a standard period. So, the space should be ventilated so that combustible levels stay at or below 10% of their LEL and toxic substances remain below their TLV.

Ventilation in confined spaces aims to control two hazards at once: flammability and toxicity. The lower explosive limit (LEL) is the gas concentration at which a mixture becomes capable of ignition; keeping combustibles well below that threshold reduces the chance of ignition if an ignition source is present. A common safety target is no more than about 10% of the LEL for combustibles. For toxic substances, the goal is to stay below the level defined by the TLV (threshold limit value), which represents a safe exposure concentration over a standard period. So, the space should be ventilated so that combustible levels stay at or below 10% of their LEL and toxic substances remain below their TLV.