Glossary / Physical properties
Flammable range
Flammable range is the span of concentrations of a gas or vapor in air, between its lower and upper explosive limits, within which the mixture can ignite or explode. Outside the range the mixture is either too lean or too rich to burn.
Explanation
Imagine slowly adding vapor to air. At first there is too little fuel to burn. At the Lower explosive limit (LEL) the mixture can ignite. As more vapor is added it stays flammable until the Upper explosive limit (UEL), past which there is too little oxygen. Everything between those two points is the flammable range, also called the explosive range.
A wide range means a flammable mixture is easier to form and harder to avoid. A narrow range gives less room for error. Substances with a low LEL and a wide range are typically the ones that need the strictest controls on ventilation and ignition sources.
The range is a property of the mixture at stated conditions. Heating the gas, raising the pressure or enriching the air with oxygen tends to widen it, while adding an inert gas such as nitrogen narrows it. This is the basis of inerting, where a vessel is purged to keep oxygen below the level that supports burning.
Being inside the range does not by itself cause a fire. You still need an ignition source with enough energy, such as a spark, hot surface or static discharge. That is why controls combine ventilation, elimination of ignition sources, and Grounding and bonding to prevent static.
What to do and watch for
- Aim to keep working concentrations far below the lower limit using ventilation and monitoring.
- Remember that any release that dilutes into air will pass through the range.
- Compare the range for each product on the SDS when choosing between solvents.
Where it appears on an SDS
- Section 9: Physical and chemical properties. Gives the explosive limits that define the range, usually as percent by volume, or says the data are not available.
- Section 5: Fire-fighting measures. May warn that vapors can form explosive mixtures with air and describe special firefighting hazards.
SDS content and wording vary by supplier. This page is general reference and does not replace the current SDS for your product.