Industrial hygiene — among the following common industrial chemicals, which substance has the highest Threshold Limit Value (TLV) for routine workplace exposure (i.e., the largest permissible time-weighted average concentration; CO2 is typically in the thousands of ppm, far above aromatic solvents)?

Introduction:
Air quality in workplaces is evaluated using Threshold Limit Values (TLVs), which are guideline concentrations for typical 8-hour shifts. This question asks which listed chemical has the largest TLV, i.e., the highest allowable time-weighted average concentration, indicating comparatively lower acute toxicity at trace workplace levels.

Given Data / Assumptions:

• Substances listed: carbon dioxide, toluene, carbon disulphide, acetaldehyde.
• Compare typical occupational exposure limits used in practice.
• We are selecting the substance with the maximum TLV (largest permissible TWA).

Concept / Approach:
TLV values are set so that most workers may be repeatedly exposed without adverse health effects. The higher the TLV, the less hazardous the substance is at low concentrations. In general, simple asphyxiants like carbon dioxide have higher TLVs than toxic solvents or reactive aldehydes.

Step-by-Step Solution:

Verification / Alternative check:
Reference values across credible sources consistently place CO2 at several thousand ppm, while the others are far lower. Thus CO2 clearly has the maximum TLV among the options.

Why Other Options Are Wrong:

• Toluene: neurotoxic solvent with limits typically in tens to low hundreds of ppm.
• Carbon disulphide: highly toxic; TLVs near single-digit ppm.
• Acetaldehyde: irritant with low ceiling values (tens of ppm).

Common Pitfalls:
Confusing TLV (allowable chronic workplace exposure) with IDLH or short peak ceilings. Another pitfall is assuming all “carbon” compounds behave similarly; toxicity differs widely.

Final Answer:
Carbon dioxide has the highest TLV among the listed substances.