Threshold Limit Value (TLV) denotes the maximum acceptable concentration for workplace exposure; the TLV (ceiling) for phosgene in air is about 0.1 ppm (parts per million).

Introduction / Context:
Phosgene (COCl2) is a highly toxic industrial gas. Occupational exposure guidelines define maximum allowable concentrations to protect worker health. TLV values are typically expressed as TWA (time-weighted average), STEL (short-term exposure limit), or ceiling limits that should never be exceeded.

Given Data / Assumptions:

• We are interested in an accepted, practical TLV for phosgene.
• Many standards cite a very low ceiling value around 0.1 ppm due to high toxicity.

Concept / Approach:
Relate health risk to dose: even brief exposures to phosgene can cause severe respiratory injury. Therefore, limits are set extremely low, and a ceiling (instantaneous) cap is appropriate for control.

Step-by-Step Solution:

Verification / Alternative check:
Cross-reference safety datasheets and occupational hygiene references that list a 0.1 ppm ceiling; different jurisdictions may use closely related values, but 0.1 ppm is widely recognized.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing TWA with ceiling limits; ignoring the need for immediate alarms and leak detection for phosgene.

Final Answer:
0.1 ppm