Inside the 32-hour operation to defuse a moving bomb on the Mumbai–Pune Expressway

At around 5 pm on February 3, evening peak-hour traffic was building along the ghat stretch near the Adoshi tunnel, a section notorious for sharp curves and steep gradients. Just over an hour later, at kilometre marker 42 on the Pune–Mumbai carriageway, a gas tanker travelling downhill lost control while negotiating the curve and overturned on its side.

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The BPCL tanker was carrying nearly 21 tonnes of propylene gas, a highly inflammable and poisonous industrial chemical, en route from Kochi to Surat. The impact damaged all three top-mounted ball valves and within minutes, liquid propylene began leaking on the road. What followed was not an accident site but the birth of a moving bomb.

Gurunath Sathelkar, founder of the Khopoli-based Help Foundation, and among the first responders to reach the spot, said the danger was immediate and deceptive.

“Propylene gas is heavier than air, so instead of rising, it flows along ground level. It spreads over a wide area and is not easily visible. Even a very small spark — something as minor as an invisible spark from a vehicle’s silencer — is enough to trigger an explosion,” Sathelkar said.

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The risk was magnified by the tanker’s load. “Propylene has an explosive ratio of around 1:250. That means even a small quantity can cause a massive blast. The impact zone could have extended nearly five kilometres from the site,” he said.

On an expressway with four to five lanes packed with vehicles, the consequences were almost unthinkable. “A 14-kg domestic LPG cylinder can destroy a house. This tanker was carrying 21 tonnes of inflammable material,” Sathelkar said.

“Given that the accident occurred in the ghat section near a tunnel on a common stretch of the expressway and NH-48, our priority was to prevent any loss of life or damage to public property. Traffic was halted at a safe distance in coordination with police, and the area was isolated, as diversion options were not available,” said a spokesperson for IRB MP Expressway Pvt. Ltd, the concessionaire operating the stretch.

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Mumbai-bound traffic was completely stopped. Fire tenders were positioned not to fight flames, but to spray water continuously to prevent heat build-up and reduce vapour concentration. Traffic wardens began halting vehicles kilometres away.

At around 7.30 pm, a specialised team from Mec Elec Industrial Services, which operates a compressed gas tanker testing station at Khalapur–located 10 kilometers from the accident site–was mobilised.

A team from the safety department of Reliance Industries is stationed at Khalapur through which several Reliance containers pass; they got in touch with Mec Elec Industrial Services. “Our Khalapur-based team, led by technical director Z.N. Gawade, received an urgent call from the Reliance Safety Department and mobilised with specialised equipment to arrest compressed gas leaks,” said Dnyanesh Madhav Divekar, the company’s executive director.

Divekar, who is a mechanical engineer with a master’s degree in safety engineering from A&M University, Texas, and experience with companies like Air Liquide and BP in the US. Divekar told HT that his team understood immediately how rare and dangerous the situation was.

The environment was already extreme. “LEL meter readings were significantly elevated even at 500 metres. That means the area was already well within a hazardous zone,” he said. LEL meter stands for Lower Explosive Limit meter—a safety device to measure the presence of flammable gases in the atmosphere.

Between 8.30 pm Tuesday and 5 am Wednesday, the team managed, after repeated attempts, to arrest two of the three leaks — one liquid and one vapour valve. The third, however, refused to yield. “We tried fabricated plugs, clamps, simple arrest tools — nothing held,” Divekar said.

“There are rescue vehicles for LPG, but propylene is different,” Divekar explained. “The design pressure of propylene is around 22 bar (propylene’s vapour pressure is measured in bars) compared to about 14.5 bar for LPG. That’s roughly 1.5 times higher. Even if an LPG rescue vehicle had arrived, it would have been useless.”

By dawn on Wednesday, it was evident that the tanker could not be sealed on site. The only viable option was decontamination — removing the gas itself.

One by one, empty tankers were arranged. Pressure differentials were carefully maintained. Hoses were attached to valves that were already loose and moving.

“It was a very precarious condition,” Divekar said. “If the weight of the hose shifted, or if a valve dislodged, it would have been catastrophic.”

Complicating matters further, all connections were in the liquid phase, meaning liquid propylene — not vapour — was flowing out. Measuring how much gas had been transferred was nearly impossible. The rotogauge was on the underside of the overturned tanker and inaccessible.

“Only when vapour started coming out that we knew roughly 50% of the product was gone,” he said.

Over several hours, the gas was transferred five to six times across three tankers. By Wednesday evening, the flow finally shifted from liquid to vapour — the first real sign that the risk had reduced.

Multiple cranes were deployed for a tandem lift, a process requiring perfect coordination. Any sudden jerk could have reopened valves.

“Our concern was that once the tanker was upright, the liquid could rush again and trigger fresh leaks,” Divekar said.

The lift was executed slowly, deliberately, without shock. Once upright, the final leaking connection was arrested using specialised leak-control techniques.

By around 9 pm, Wednesday, all leaks were sealed.

Divekar too dismissed criticism that traffic closures were excessive.

“The lower explosive limit of propylene is just 2%. If even 2% propylene mixes with air, it becomes flammable,” he said. “At one point, we recorded 20% of the LEL even 500 metres away. All you needed was a source of ignition — a phone, a silencer, static electricity.”

Near a tunnel, the risk multiplied. “In confined or semi-confined spaces, gas concentrations persist much longer,” he said.

The MSRDC officials accepted that entire operation took longer than expected to finish. According to MSRDC Executive Engineer Rakesh Sonawane, to ensure minimal inconvenience to motorists, orders were issued by the Mumbai division to suspend toll collection until traffic on the Mumbai-bound carriageway is fully restored.