Explosion limits – blast furnace gas safety range Blast furnace gas has explosion limits of 37–71% gas (by volume) in a gas–air mixture. In a confined space, it will explode when its concentration is:

Introduction / Context:
Explosion (flammability) limits define the composition range over which a fuel–air mixture can ignite and propagate flame. Outside this range, mixtures are either too lean or too rich to sustain combustion. Knowledge of limits is essential for safe handling of industrial gases like blast furnace gas (BFG).

Given Data / Assumptions:

• BFG explosion limits: lower = 37 vol%, upper = 71 vol% fuel in air.
• Confined space with an ignition source present.
• Standard pressure and temperature conditions assumed for the stated limits.

Concept / Approach:
For an explosion to occur, the fuel concentration must lie between its lower explosion limit (LEL) and upper explosion limit (UEL). Below LEL the mix is too lean; above UEL it is too rich (insufficient oxygen). Thus a mixture will explode only when the concentration lies within the quoted range of 37–71%.

Step-by-Step Solution:

Verification / Alternative check:
Similar interpretation applies to other industrial gases; e.g., methane LEL ≈ 5% and UEL ≈ 15% in air.

Why Other Options Are Wrong:

• < 37%: Too lean to sustain flame.
• > 71%: Too rich; oxygen deficient for propagation.
• None: Incorrect since a valid range exists.

Common Pitfalls:
Ignoring that ventilation, temperature, and pressure can shift limits slightly; always design with safety margins.

Final Answer:
between 37% and 71%