Safety engineering: Which gas among the following has the widest flammability (explosive) limits in air, making it the most hazardous in this respect?

Introduction / Context:
Flammability (explosive) limits define the range of fuel-air mixtures that can propagate flame. Wider limits indicate a gas is more easily ignitable over a broader concentration range, increasing handling and storage risk.

Given Data / Assumptions:

• Standard conditions near ambient temperature and pressure.
• Typical lower and upper flammability limits (LFL/UFL) in air.
• Gases considered: acetylene, hydrogen, carbon monoxide, gasoline vapor.

Concept / Approach:
Acetylene has exceptionally wide limits (approx. LFL ~2.5% to UFL ~81% by volume in air). Hydrogen is also wide (~4% to 75%), but narrower than acetylene. Carbon monoxide (~12.5% to 74%) and gasoline vapor (range varies with composition, generally narrower) are less extreme.

Step-by-Step Solution:
1) Compare LFL/UFL: determine width = UFL − LFL.2) Acetylene: ~78.5% width; Hydrogen: ~71% width; CO: ~61.5% width; Petrol vapor: narrower and temperature dependent.3) Conclude acetylene exhibits the widest flammability range.

Verification / Alternative check:
Chemical safety datasheets and fire protection handbooks consistently report acetylene's extremely wide explosive limits, necessitating strict flashback and backfire controls in oxy-acetylene systems.

Why Other Options Are Wrong:
Hydrogen: Very wide, but still narrower than acetylene.CO: Wide but not the widest among those listed.Petrol vapor: Composition-dependent and generally narrower than acetylene.

Common Pitfalls:
Assuming hydrogen is always the most hazardous due to low ignition energy; range width also matters.Ignoring the role of temperature and oxygen enrichment on limits.

Final Answer:
Acetylene