Occupational exposure guideline for carbon monoxide (CO) What is the commonly cited threshold limit value (TLV-TWA) for CO in workplace air, expressed in parts per million (ppm)?

Introduction / Context:
Carbon monoxide (CO) is a colourless, odourless gas produced by incomplete combustion. It binds to haemoglobin to form carboxyhaemoglobin, reducing oxygen delivery to tissues. Workplace exposure limits aim to prevent acute toxicity and protect worker health during an 8-hour shift.

Given Data / Assumptions:

• TLV-TWA refers to an 8-hour time-weighted average limit.
• We are selecting a single, widely taught benchmark value for MCQs.
• Short-term exposure limits and ceiling values are not requested.

Concept / Approach:
A commonly cited occupational guideline is a TLV-TWA of 50 ppm for carbon monoxide. Although various jurisdictions and agencies can publish slightly different limits, 50 ppm appears frequently in educational materials and historic ACGIH references, making it the standard exam answer unless a specific regulatory source is specified.

Step-by-Step Solution:

Verification / Alternative check:
Safety manuals and industrial hygiene handbooks frequently present 50 ppm as the TWA benchmark for instructional purposes.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing TWA with short-term or emergency exposure guidance; mixing up CO with CO2 limits.

Final Answer:
50