Sulphur differs from most other combustible dusts found in the industry, as physically it has a low melting point of 119°C, has a low ignition temperature of 190°C and as a liquid, is flammable and sulphur vapours are explosive. Sulphur dust is also characterised with low Minimum Ignition Energy (MIE) of 3–10 mJ and hence dust clouds can be readily ignited by weak electrostatic or mechanical spark. Any dusts containing 25% or more elemental sulphur may be considered as almost as explosive as pure sulphur
Possibilities of a sulphur dust explosion
The dust must be able to form a cloud.
The particle size should be small enough to allow propagation.
The concentration of dust cloud must be above the Minimum Explosible Concentration (MEC).
There must be sufficient oxygen in the atmosphere to support and sustain combustion, i.e. Oxygen content should be more than Limiting Oxygen Concentration (LOC).
A source of ignition must be present with an energy higher than the Minimum Ignition Energy (MIE).
Note: This article provides general good engineering practices while handling sulphur, based on the experience of the Sigma-HSE Consultants and should not be considered as guidelines. For specific risk assessment of your facility, expert advice is necessary from an appropriate specialist safety company such as Sigma-HSE. Additional guidance can also be taken from NFPA 655 (Standard for Prevention of Sulphur Fires and Explosions, 2017 Edition).
