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

At around 5 pm on February 3, there was heavy traffic on the ghat section near the Adoshi tunnel in the evening peak-hour, which is notorious for sharp turns and steep slopes. Exactly an hour later, at kilometer marker 42 on the Pune-Mumbai carriageway, a downstream gas tanker lost control while taking a turn and overturned on its side.

The BPCL tanker was carrying about 21 tonnes of propylene gas, a highly flammable and poisonous industrial chemical, en route from Kochi to Surat. The impact damaged all three ball valves overhead and within minutes liquid propylene began leaking onto the road. What happened next was not a crash site but the birth of a moving bomb.

an invisible, spreading threat

Propylene behaves unlike most gases in that it does not rise and diffuse into the air, but instead collects and flows quietly along the ground.

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

“Propylene gas is heavier than air, so instead of rising up, it flows along the 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 coming from a vehicle’s silencer – is enough to cause an explosion,” Sathelkar said.

The danger had increased due to the load in the tanker. “The explosive ratio of propylene is about 1:250. This means that even a small amount can cause a huge explosion. The impact zone can extend up to about five kilometers from the site,” he said.

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

First Response: Isolate, Don’t Touch

The accident was reported to the expressway control room and the highway traffic police within minutes and the injured driver and his assistant were given medical aid and taken to hospital. Responders had already realized that recovery was impossible without prevention.

A spokesperson of IRB MP Expressway Pvt Ltd said, “Given that the accident occurred at 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. In coordination with the police, traffic was stopped at a safe distance and the area was isolated, as diversion options were not available.” Ltd., the concessionaire operating this section.

The traffic going to Mumbai was completely stopped. Fire tenders were deployed not to fight the flames, but to continuously spray water to prevent heat from rising and reduce the concentration of vapor. Traffic wardens started stopping vehicles several kilometers away.

A technological nightmare takes shape

By nightfall the scale of the problem became clear. All three valves on the tanker were leaking – two could be reached with difficulty, but the third was badly bent, its handle jammed against the weld cap, and it continued to discharge liquid propylene at high pressure.

At around 7.30 pm, a special team from Mech Elek Industrial Services, which operates a compressed gas tanker testing station at Khalapur – located 10 kilometers from the accident site – was deployed.

A team from the security department of Reliance Industries is deployed at Khalapur, where many Reliance containers pass through; He contacted Make Elec Industrial Services. “Our Khalapur-based team led by technical director ZN Gawde received an urgent call from the Reliance safety department and mobilized with special equipment to stop the compressed gas leak,” said company executive director Gyanesh Madhav Diwekar.

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

The atmosphere was already at its peak. “The LEL meter reading was significantly elevated even at 500 metres. This means the area was already in the danger zone,” he said. LEL Meter stands for Lower Explosive Limit Meter – a safety device for measuring the presence of flammable gases in the atmosphere.

Between 8.30 pm on Tuesday night and 5 am on Wednesday, the team, after repeated attempts, managed to stop two of the three leaks – a liquid and a vapor valve. However, the third refused to bow. “We tried fabricated plugs, clamps, simple arresting devices – nothing held in place,” Diwekar said.

Why did traditional rescue equipment fail?

The obvious question – why a standard gas rescue vehicle is not used – received a serious answer.

“There are rescue vehicles for LPG, but propylene is different,” Diwekar said. “The design pressure of propylene is about 22 bar (the vapor pressure of propylene is measured in bars), compared to about 14.5 bar for LPG. This is about 1.5 times higher. Even if an LPG rescue vehicle had arrived, it would have been useless.”

By Wednesday morning it became clear that the tanker could not be sealed on the spot. The only viable option was decontamination – removing the gas itself.

Most dangerous step: filtering the gas

Senior officials of the police, MSRDC, NDRF and disaster management agencies agreed to a high-risk plan: transferring the gas into empty propylene tankers under controlled conditions.

Empty tankers were arranged one by one. The pressure difference was carefully maintained. The hoses were connected to valves that were already loose and rotating.

“It was a very precarious situation,” Diwekar said. “If the weight of the hose had shifted, or the valve had dislocated, it would have been catastrophic.”

Making matters more complicated, all of the connections were in liquid phase, meaning that liquid propylene – not vapor – was flowing out. It was almost impossible to measure how much gas was transferred. The rotogage was on the bottom of the overturned tanker and was inaccessible.

“It was only when steam started coming out that we realized that about 50% of the product was gone,” he said.

Over several hours, the gas was transferred five to six times to three tankers. By Wednesday evening, the flow finally changed from liquid to vapor – the first real sign that the risk had diminished.

Straightening the Tanker: Zero Tolerance for Error

With the load eased, officials prepared for the next important step: lifting the tanker.

Multiple cranes were deployed for the tandem lift, a process that requires complete coordination. Any sudden shock could cause the valves to open again.

“Our concern was that once the tanker was upright, the fluid could rise again and cause a fresh leak,” Diwekar said.

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

All the leaks were stopped by around 9 pm on Wednesday night.

Final Withdrawal – and why privacy matters

At about 1.30 am, the tanker was finally towed away from the accident site and towed at low altitude to a safe, undisclosed location, where the remaining gas was transferred to an even more delicate operation.

Why did the expressway have to be closed?

Raigarh Superintendent of Police Aanchal Dalal stressed that despite the pressure to restore traffic, safety protocols cannot be compromised. “Our objective was to ensure that all safety protocols are strictly followed while expediting the operation,” Dalal said. “We made every effort to restore smooth traffic flow by Wednesday night itself, without compromising public safety,” he said.

Diwekar also rejected criticism that the traffic shutdown was excessive.

He said, “The lower explosive limit of propylene is only 2%. If even 2% of propylene gets mixed in the air, it becomes inflammable.” “At one point, we recorded 20% LEL even 500 meters away. All you needed was a source of ignition – a phone, a silencer, static electricity.”

Near a tunnel, the risk increases manifold. “In confined or semi-confined spaces, gas concentrations persist for longer periods of time,” he said.

MSRDC officials admitted that the entire operation took longer than expected to finish. According to MSRDC executive engineer Rakesh Sonawane, to ensure minimum inconvenience to motorists, orders were issued by the Mumbai division to suspend toll collection until traffic is completely restored on the Mumbai-bound carriageways.