This accident took place on a holiday, the all important indian festival of Diwali, which is believed to be the reason why the number of casualties were much lower than what would have been on a normal working day. The date was 9th November, 1988, wednesday, and only some essential activities were being carried out, which included the loading of rail tank wagons. It was lunch time, and actual loading operations had been temporarily suspended. Workers were taking lunch, sitting in small groups in the open areas of the distribution unit. Some had retired to the lunch rooms away from the site of the fire.

At the time of the accident, product was being pumped from the Refinery into storage tanks. While there are no authentic documents on the cause of the accident, it is believed that one of the storage tanks, a fixed roof tank, which was receiving a light naphtha product, got overfilled and ruptured (this could have been due to the failure of the level indicator in this tank, which was recorded a few days prior to the incident or an operator error). Due to the rupturing of the storage tank, a huge amount of the liquid hydrocarbon was released, resulting in the formation of a large vapour cloud. This vapour cloud drifted downwind till it encountered a source of ignition in the form of the naked flame of the coal tar boiler.

The resultant vapour cloud explosion caused a tremendous heat wave, which affected an area approximately 150 metres in radius, covering the Aromatic tankfarm, its pumphouse, area used for despatch of packing bitumen, and the rail tank wagon loading gantry. Some survivors recalled hearing two or three explosions in short intervals before the fire engulfed the area. Thick black clouds darkened the sky above the refinery as a number of fires were ignited due to the vapour cloud explosion. The explosions were heard upto a radius of 5 kms and the flames could be seen from as far as 20 kms.

Employees of the Refinery, residing in nearby township, on hearing of the disaster, rushed to the site, and helped moving the injured persons to the medical centre for first aid. The injured personnel were quickly shifted to outside hospitals, and this was done within an hour of the accident. The Bombay fire brigade also responded, and there were 15 fire tenders in operation by 1.00 p.m., which included the Refinery's own personnel and mutual aid members. By 2.00 p.m., the fire in the bitumen and PDF gantry, and all other fires except the fire in the tankfarm were completely put out. Fire fighting operations were fully directed to the tankfarm areas where one tank and the surrounding area was totally engulfed in flames.

Maintenance of supplies to the fire site from the fire station, was established immediately after the fire, and ensured timely supply of hoses, sand, different types of foams, dry chemical powder, small portable extinguisher and other specialised equipment needed at the fire site. Most fires were fully under control by mid-day on the 10th and finally put out by 4.00 p.m. Full control was established in 20 hours and it took a total of 28 hours to put out the last remnants of the fire. In the final analysis, 34 people were killed, and 29 severely injured. Losses were estimated at over Rs. 100 million (at that time).

Mahul Refinery Explosion/ fires - effects and consequent safety upgradation

This was probably the most serious refinery fire incident in the country till that time, and considering the life and property losses, one of the major industrial fires worldwide. The destructive power of experienced first hand by the indian industry. The physical a vapour cloud explosion was damage to the refinery was quite less, when compared to similar accidents elsewhere. However, the loss of life was substantial, even for a densely populated country like India, and led to radical changes in the indian industrial safety scenario. A government enquiry was instituted to look into the accident and suggest improvements. The Oil Industry Safety Directorate (OISD), which till then had an advisory role, now became the steering body for safety in the oil industry. It became fully active in the development of safety standards, and carrying out inspections/ audits of petroleum/ oil installations in the country. Many norms with respect to industry design and operations, were revised and newer codes published. Recognising the problems faced during the firefighting operations, especially in the storage tank farm area, many new rules concerning inter-tank distances, tank dikes heights and oil-water separators were introduced and implemented.