Key values
Source: IEC 60079-20-1:2010 data table.
Explosive range and ppm values
Benzene can ignite when mixed with air between 1.2 % and 8.6 % 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 and g/m³. Useful to compare a gas detector's %LEL reading with ppm values in a measurement report.
| Concentration | ppm | g/m³ (20 °C) |
|---|---|---|
| 1 LEL (100 %LEL) | 12,000 | 39.0 |
| 20 %LEL | 2,400 | 7.79 |
| 10 %LEL | 1,200 | 3.90 |
Lighter or heavier than air?
Benzene vapour is heavier than air: relative density 2.70 (air = 1). A release 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 benzene is −11 °C, the boiling point 80.1 °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 above 35 °C, it is a Category 2 flammable liquid under the CLP Regulation: H225 “Highly flammable liquid and vapour”, signal word “Danger”.
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 498 °C. The maximum surface temperature of equipment in the zone must stay below it: all temperature classes (T1–T6) are suitable.
- T1450 °C suitable
- T2300 °C 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 in refineries and petrochemical plants; used as a raw material in the chemical industry. It is carcinogenic: besides its flammability, 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: IEC 60079-20-1:2010 data table.
The relative density is calculated from the molar mass (M / 28.96). The ppm and g/m³ values apply at 20 °C and 1 atm (molar volume 24.055 L/mol). The temperature class follows the rule that the surface temperature must stay below the autoignition temperature.
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 benzene in ppm?
1.2 % by volume, that is 12,000 ppm. 10 %LEL corresponds to 1,200 ppm and 20 %LEL to 2,400 ppm.
Is benzene heavier than air?
Yes, its vapour is heavier than air. Relative density 2.70 (air = 1): a release sinks and can collect in pits, trenches and drains.
Which Ex equipment is suitable for benzene?
Temperature class: any class from T1 to T6. 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 benzene?
−11 °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 2 flammable liquid (H225).