Pharma factory blast: Evidence suggests dust explosion, say experts about the blast

Safety protocols in pharmaceutical industries of the city have come into sharp focus yet again in the context of the latest blast in the manufacturing facility of Sigachi Industries in Pashamylaram on Monday (July 1, 2025) in which dozens were killed.

While the Factories Department is still collecting evidence, experts who have observed the footage of the blast site conclude that it is a ‘dust explosion’. They contend the version of the Factories Department, which, based on prima facie evidence, explains it as the ‘Boiling Liquid Expanding Vapour Explosion’ (BLEVE), a technical term to mean that the pressure build up inside the reactor led to the blast.

As per the text book definition, BLEVE occurs when a pressurised vessel containing a liquid is heated to a temperature significantly higher than its boiling point at atmospheric pressure, causing the vessel to rupture and the liquid to rapidly vaporise.

Zuber Ali Khan, a fire forensics expert in the city, refutes the theory and concludes that it is dust explosion.

“Dust explosion has five effects. One is a positive wavefront, which explains the outward push and negative wavefront, which immediately sucks it back. Looking at the blast scene, I can prima facie conclude that it is dust explosion and not BLEVE. Then there are fragment impact, ground shock and dynamic drag loads which need to be analysed minutely at the blast site,” Mr. Khan says.

While every fire needs combustible material, heat source and oxygen, it is also important to analyse how the fire moved from one point to the other, he says.

Sigachi Industries is engaged in manufacture of microcrystalline cellulose (MCC) powder, which acts as a binder, disintegrant, filler, and lubricant in pharmaceutical production.

“The manufacturing process involves sending hot air into the drier which sucks out the moisture from cellulose, to turn it into a fine powder. When the dust microns accumulate to certain concentration in the confined space subject to certain atmospheric conditions, explosion could occur,” says retired scientist K. Babu Rao who also surmises it to be a dust explosion.

The ignition temperature required for a dust explosion is very low at 232°C, and the process should ensure that the temperature stays below the point. Mr. Babu Rao estimates the energy generated in the Sigachi explosion to be equal to 400 kilogram TNT blast. He puts the blame squarely on the Factories Department for the spree of industrial accidents in the State.

“They are supposed to conduct regular inspections, which they don’t. In the event of blasts, they give favourable reports to the companies,” he says. The report of the expert committee constituted by the department after the blast in a reactor of the SB Organics Limited of Sangareddy district in April, 2024, has not been out till now, he says.

Another pharma company blast in the city last year was attributed by the department to static electricity, giving clean chit to the company, and holding the workers responsible for not wearing safety gear, he says.