Key values
Source: compilation of GESTIS, NIOSH and ISO/IEC 80079-20-1 data; the conservative end of the range between sources (lowest LEL and AIT, highest UEL). Diesel is a mixture; the minimum flash point comes from EN 590, the explosive limits from GESTIS (approximate) and the autoignition temperature is the low end of the range between sources. The product's safety data sheet applies.
Explosive range and ppm values
Diesel can ignite when mixed with air between 0.6 % and 6.5 % 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?
Diesel 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 diesel is above 55 °C, the boiling range 141–462 °C.
Under the note to Table 2.6.1 in Annex I of the CLP Regulation, gas oils, diesel and light heating oils with a flash point between 55 and 75 °C may be regarded as Category 3 (H226 “Flammable liquid and vapour”).
As the flash point of diesel is above normal ambient temperatures, an ignitable vapour does not usually form above the liquid, which is why diesel is usually not treated as a source of release at filling stations. An explosive atmosphere can form in two cases: when the liquid heats up close to or above its flash point (for example a leak onto a hot surface) and when it is sprayed under pressure as fine droplets (mist). A mist can ignite even below the flash point. The explosion protection document assesses diesel tanks and lines for these two cases.
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, in generator fuel tanks and day tanks, in fuel stores for machinery and vehicle fleets, and as a boiler fuel.
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: compilation of GESTIS, NIOSH and ISO/IEC 80079-20-1 data; the conservative end of the range between sources (lowest LEL and AIT, highest UEL). Diesel is a mixture; the minimum flash point comes from EN 590, the explosive limits from GESTIS (approximate) and the autoignition temperature is the low end of the range between sources. 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: n-hexadecane (cetane)): Wikimedia Commons, Hexadecane-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 diesel 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 diesel 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 diesel?
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 diesel?
Above 55 °C.