What exactly is Aerosol Explosion? One of the least discussed types of explosion scenario, where Aerosol produced from combustible liquid, even at room temperature and situation below the combustible liquid’s flash point could explode given an available ignition source.
As per Gant, in a report for HSE, aerosol is defined as “colloidal dispersion of solid or liquid particles mixed in gas”. One important aspect of aerosols is that we can observe and see them in our everyday lives, such as spray deodorant, air freshener, furniture polish, etc. Due to the fact that aerosol is basically a mixture of liquid and gas, liquid hydrocarbon fuel is able to mix with air to form hydrocarbon aerosol, and these hydrocarbon aerosols pose not only fire risk but also explosion risk, subject to dispersion condition and containment of the system i.e. Lower Explosive Limit / Lower Flammability Limit.
To discuss our risk reduction approach, first we need to know the situations at which aerosol could be produced.
There are several ways aerosol can be formed from liquid fuel below its flash points. As suggested by Gant and HSE, which include: high pressure release, condensation, air stripping, and agitation / splashing.
So our risk reduction approach starts with proper Fire & Explosion Risk Assessment and Hazard Analysis of process whenever applicable. This is to correctly identify the possible scenarios at which aerosol, especially hydrocarbon aerosol could be produced. Focus on a high pressure system which usually comes using a hose and pump system. Systems such as hydraocarbon fuel lines, or something as mundane as a lubrication oil pump, are most susceptible to wear and tear, especially at weak points such as connections and hose. A miniscule of tear from the hose surface could produce a jet of spray of lubrication oil and thus lube oil aerosol is produced. If ignited and at the Lower Flammability Limit range, an Aerosol Explosion could occur.
The size of the orifice or rupture dictates the dispersion of liquid fuel, and whether or not Aerosol is produced. Dispersion is also an important factor as it dictates the particle size which affects the overall Minimum Ignition Energy. Therefore, a pinhole rupture of a pressurized, diesel fuel line could produce Diesel Fuel Aerosol which pose as an explosion hazard – even below the liquid fuel’s flash point.
Still within the realm of Fire & Explosion Risk Assessment and Hazard Analysis, pay attention at which compressed air system is utilized, and if there is any available combustible liquid fuel nearby. In the right circumstances, the compressed air can impinge on the combustible liquid pool, and produce aerosol.
Another point of interest is the process itself, and whether the combustible liquid utilized in the process can react a certain way that produces aerosol. Condensation of combustible liquid should also be looked at, specifically for facilities with temperature difference or situated in climate within the condensation limit of the fuel.
Due to the various ways aerosols can be formed, it is clear to see why aerosol explosions pose as a threat, especially in chemical and process industries. In 2009, Santon conducted an incident survey related to the ignition of mist / aerosol formed from flammable liquids at temperature below their flash points, and concluded that the frequency of incidents is far greater than previously thought.
Fahri Ali Imran