If an explosimeter spikes then drops, what does this indicate?

If an explosimeter spikes then drops, what does this indicate?

• A. Safe atmosphere
• B. No gas present
• C. Low oxygen
• D. Over flammable range

Answer: (D)

A transient spike on an explosimeter shows the atmosphere briefly reached a combustible concentration. In gas safety terms, the flammable range spans from the lower explosive limit (LEL) to the upper explosive limit (UEL). When the reading spikes, the gas concentration momentarily climbed into that range, meaning ignition could be possible if an ignition source were present. The subsequent drop means the concentration fell back below the LEL, likely due to dilution, ventilation, or gas dispersion. So, the spike-and-drop pattern indicates a temporary entry into the flammable range rather than a completely safe or inert atmosphere. This is why immediate actions—stop work, ventilate, locate and mitigate the source, and recheck the atmosphere—are warranted. The other options don’t fit as well: a truly safe atmosphere would maintain readings at or near zero or consistently below the LEL; there’s gas present if the meter spikes; oxygen level isn’t what the meter measures here, and a condition described as being over the flammable range would imply a concentration above the UEL, which is not what a brief spike followed by a drop represents.

A transient spike on an explosimeter shows the atmosphere briefly reached a combustible concentration. In gas safety terms, the flammable range spans from the lower explosive limit (LEL) to the upper explosive limit (UEL). When the reading spikes, the gas concentration momentarily climbed into that range, meaning ignition could be possible if an ignition source were present. The subsequent drop means the concentration fell back below the LEL, likely due to dilution, ventilation, or gas dispersion.

So, the spike-and-drop pattern indicates a temporary entry into the flammable range rather than a completely safe or inert atmosphere. This is why immediate actions—stop work, ventilate, locate and mitigate the source, and recheck the atmosphere—are warranted.

The other options don’t fit as well: a truly safe atmosphere would maintain readings at or near zero or consistently below the LEL; there’s gas present if the meter spikes; oxygen level isn’t what the meter measures here, and a condition described as being over the flammable range would imply a concentration above the UEL, which is not what a brief spike followed by a drop represents.