The unit having an authorisation to use the material except hydrogen gas was found manufacturing the chemicals. On the 2nd of June 2020, the chemicals known as DMS and Nitric Acid brought by different tankers were to be unloaded. Without following the strict procedure for downloading the chemicals which are hazardous, the person not operating as an operator in the tank farm area unloaded the material however, the Nitric Acid was unloaded in the tank of DMS and the DMS was unloaded in the tank of Nitric Acid. Despite the knowledge of the mixing of incompatible chemicals, the chemical engineers of the unit did not think it fit to shut down the plan but on the contrary, continued their activities and even on the next day the unit operated on 3rd June, as usual. The mixture on account of heating in view of the nature of the chemicals, exploded and the fire took place as a consequence 11 persons died, many sustained grievous hurt and many sustained simple hurts.
Cause of the accident
- Management as a whole is responsible for allowing the person not appointed as a tank farm operator to unload the chemicals, when they were aware that the tank farm operator left the tank farm area.
- Proper procedure was not followed while unloading the chemicals.
- The senior officers who came at the tank farm and discussed the subject of mixing of the chemicals failed to take appropriate action as required and allowed the unit to operate as usual.
- Incompatible chemicals stored close to each other
- No automatic temperature alarm/ siren/ hooter to alert in case the temp rises beyond a limit.
Some Important Recommendations
- Installation of temperature indicator along with alerts/ siren/ hooter at higher temperatures to warn before an emergency.
- The temperature should be reflected in the DCS
- The safety valve of the storage tank is to be checked regularly and be recorded in the appropriate register.
- There should be a risk assessment study of chemical plants at certain intervals.
- Different socket design for incompatible chemicals to prevent incorrect transfer. The different sizes of couplings of tanks and the pipe connecting the tanker.
- The tank farm operator must get the connection certified by a responsible officer namely, shift-in-charge / H.O.D. before unloading commences.
- Tank farm operators must be a qualified with certain experiences.
- CCTV must be installed in tank farm area with two data storages, at least one outside to access information even in case of unforeseen event.
- Training to staff.
- Restricting the number of tankers entering the tank farm area at once.
- SOP for loading and unloading must be strictly followed.
- The storage of compatible and incompatible material should be at different places. The minimum separation distance between the storage tank and dyke wall surrounding the tank shall be half of the height of the storage tank. The height of dyke should be on fourth of the height of the tank which should be of RCC structure of appropriate width. This will reduce the effect of any explosion.