Experience has shown that explosions in ovens and dryers can happen very quickly. The key hazard is an explosion from the build up of solvent vapors in the oven or dryer atmosphere. This buildup could occur by a malfunction in the production process such as:
- a sudden or improper amount of coating
- a change in ventilation controls
- excessive speed
In any of these cases, the concentration of flammable vapor has an opportunity to rise above safe levels, creating a potentially explosive mixture of vapor in air.
Flammability is temperature dependent. Heated combustible vapor mixtures are more easily ignited. A lower concentration can support combustion, so the LFL is reduced.
For heated industrial processes such as dryers, ovens, and furnaces, the temperature effect is significant. Typically the LFL is determined at “room temperature” – either 20ºC or 25ºC. For higher process temperatures, flammability increases (and the LFL declines) as much as eight to fifteen percent or more for every 100ºC increase in process temperature.
- For example, at 220ºC, the LFL of Acetone may fall to 2.1% by volume, so that 1.25% Acetone in air is therefore 60% LFL at 220ºC compared to 50% LFL at 20ºC, a significant difference.
Unless corrected, the temperature effect can cause readings and alarms to be inaccurate – the alarm may activate less promptly and at a higher concentration than is considered safe.