Acute toxicity threshold for phosgene (COCl2): Approximate threshold limit value (TLV) / maximum permissible safe level for occupational exposure to phosgene gas is in which range (ppm)?

Introduction / Context:
Phosgene is a highly toxic pulmonary irritant historically used as a chemical warfare agent and currently encountered in certain chemical manufacturing contexts. Knowing its very low permissible exposure limit is critical for worker safety and emergency planning.

Given Data / Assumptions:

• Question asks for order-of-magnitude TLV in ppm.
• Standard 8-hour time-weighted exposure is implied; ceiling limits for phosgene are extremely low.

Concept / Approach:
Phosgene reacts with lung tissue, causing delayed pulmonary edema; symptoms can be insidious. Occupational limits are set well below 1 ppm, often at tenths of a ppm as ceiling values. Therefore, the correct selection is the less than 1 ppm category, reflecting the extreme toxicity and the need for rapid detection and stringent containment.

Step-by-Step Solution:

Verification / Alternative check:
Material safety data and regulatory tables list phosgene with very low ceiling values, typically around 0.1 ppm, confirming the selection.

Why Other Options Are Wrong:

Common Pitfalls:
Underestimating delayed onset; even small exposures require medical observation due to potential late-developing edema.

Final Answer:
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