Key values
Source: GESTIS substance database (IFA, October 2026). Petrol is a mixture; the GESTIS values are approximate (LEL and UEL approximate, autoignition about 220 °C, flash point below −35 °C, boiling range 30–215 °C). The product's safety data sheet applies.
Explosive range and ppm values
Petrol can ignite when mixed with air between 0.6 % and 8 % by volume. Below the LEL the mixture is too lean to ignite, above the UEL too rich. A rich mixture re-enters the range when it is diluted with air, so concentrations above the upper limit are not safe either.
The lower explosive limit in ppm. Useful to compare a gas detector's %LEL reading with ppm values in a measurement report. A mixture has no single molar mass, so no g/m³ value is given; check which gas the detector is calibrated for.
| Concentration | ppm |
|---|---|
| 1 LEL (100 %LEL) | 6,000 |
| 20 %LEL | 1,200 |
| 10 %LEL | 600 |
Lighter or heavier than air?
Petrol vapour is heavier than air: its components have several times the molar mass of air (29 g/mol). Vapour from a spill sinks and can collect in pits, trenches, drains and basements and travel a long way along the ground.
Flash point and liquid category
The flash point of petrol is below −35 °C, the boiling range 30–215 °C. As room temperature (20 °C) is above the flash point, an ignitable vapour can form above the surface of an open container or a spill.
With a flash point below 23 °C and boiling point at most 35 °C, it is a Category 1 flammable liquid under the CLP Regulation: H224 “Extremely flammable liquid and vapour”, signal word “Danger”.
Petrol is highly volatile. With a flash point below −35 °C, an ignitable vapour forms even in winter above an open container, a spill or a tank vent. At filling stations the dispensers, tank manholes and vent outlets and the tanker unloading point are therefore assessed as sources of release.
For another liquid, use the flammable liquid category calculator. The product label and safety data sheet apply; mixtures have different values.
Ex equipment selection
Autoignition temperature 220 °C. The maximum surface temperature of equipment in the zone must stay below it: T3, T4, T5 and T6 are suitable; T1 and T2 are not, because the limit is not below the autoignition temperature.
- T1450 °C not suitable
- T2300 °C not suitable
- T3200 °C suitable
- T4135 °C suitable
- T5100 °C suitable
- T685 °C suitable
- IIA suitable
- IIB suitable
- IIC suitable
Gas group IIA: equipment marked IIA, IIB or IIC may be used. The equipment protection level (EPL: Ga, Gb, Gc) depends on the zone, not on the substance; the zone is decided in the explosion protection document from the release and the ventilation. Specific conditions in the certificate (X) and the ambient temperature range are checked separately.
Where is it found?
Found at filling stations, fuel tanks and filling points, in areas with petrol generators and machinery, and in vehicle workshops. It contains carcinogenic components (benzene): the health hazard is assessed separately.
Where these values sit in the explosion protection document
- Substance properties. The first step of the document is to record these values, with their source, for every flammable substance on site.
- Hazardous area classification. The lower explosive limit and the density are inputs to the release calculation and to the direction in which the zone extends.
- Equipment selection. The temperature class and the gas group decide whether Ex equipment in the zone is suitable.
This page does not decide zones. The type and extent of a zone are calculated from where, how often and how much is released, and from the ventilation.
Sources
Explosive limits, autoignition temperature, gas group, flash and boiling point: GESTIS substance database (IFA, October 2026). Petrol is a mixture; the GESTIS values are approximate (LEL and UEL approximate, autoignition about 220 °C, flash point below −35 °C, boiling range 30–215 °C). The product's safety data sheet applies.
A mixture has no single molar mass, so no relative density figure is given; the ppm values follow from the percentage by volume (× 10,000). The temperature class follows the rule that the surface temperature must stay below the autoignition temperature.
Molecule model (representative component: isooctane (2,2,4-trimethylpentane)): Wikimedia Commons, Isooctane-3D-balls.png (public domain).
This page is for information. For the substance on your site, the current safety data sheet (section 9) and the relevant standards apply. All substances are in the explosive limits table.
Frequently asked questions
What is the LEL of petrol in ppm?
0.6 % by volume, that is 6,000 ppm. 10 %LEL corresponds to 600 ppm and 20 %LEL to 1,200 ppm.
Is petrol heavier than air?
Yes, its vapour is heavier than air: its components have several times the molar mass of air. Vapour from a spill sinks and can collect in pits, trenches and drains.
Which Ex equipment is suitable for petrol?
Temperature class: T3, T4, T5 or T6 (T1 and T2 not suitable). Gas group: equipment marked IIA, IIB or IIC. The protection level (EPL) depends on the zone decided in the explosion protection document, not on the substance.
What is the flash point of petrol?
Below −35 °C. As room temperature is above it, an ignitable vapour can form above an open container or a spill. Under CLP it is a Category 1 flammable liquid (H224).