The last post involved a fire in a nightclub. This month we’re looking at one of the worst industrial accidents in the world and its background. On the 19th of November 1984 in the town of San Juan Ixhuatepec in Mexico a devastating industrial accident occurred at a tank farm.
Background
We all know that the world needs energy. Our cars run on petrol and diesel, our food is delivered in diesel powered trucks, planes use aviation fuel and our homes are heated by gas or electricity generated by steam from boilers. In industry solvents such as hexane, acetone and other hydrocarbons are used in processes such as paint and coatings manufacture, plastics production and many other industrial processes. These fuels and solvents are highly flammable and are invariably bulk stored in large tanks at tank farms. In the event of a fire at such a facility there exists the danger of a boiling liquid expanding vapour explosion or BLEVE (usually pronounced Blevvy) for short.
Industrial Fire – Boiling Liquid Expanding Vapour Explosion (BLEVE)
If a liquid is held at a temperature above its normal boiling point under pressure and the container is damaged, then a BLEVE is possible. The loss of pressure causes the instantaneous explosive transition from liquid to vapour, that is the liquid boils. If the subsequent vapour is flammable a massive explosion and fireball can occur. This is known as a vapour cloud explosion or VCE.
A BLEVE doesn’t necessarily involve flammable liquids and they can even be caused by water such as in a boiler. BLEVEs can also occur with liquified gasses such as liquid nitrogen and other refrigerants and cryogens. The danger in this situation is that people coming into contact can be frozen or suffer frost bite from the rapid cooling. Asphyxiation is also a danger with inert gasses.
Storage Tanks
Tanks are designed to withstand high pressures, but a fire near a tank could heat the contents and the pressure increase could rupture the tank. Tanks are usually equipped with pressure release valves that are designed to prevent this, but the tank can still fail if the pressure is not released quickly enough. Release valves should be of such a size that the liquid is slowly allowed to boil off until the tank is empty. Localised heating of a tank particularly in an area where there is no liquid to disperse the heat can cause the metal to fail.
The Facility
The facility, owned by Petroleos Mexicanos (PEMEX) was a storage facility for liquified petroleum gas or LPG. It consisted of 54 LPG storage tanks; 6 large spherical tanks, four holding 1,600 cubic metres and two holding 2,400 cubic metres and 48 smaller horizontal bullet shaped tanks of various sizes. All together the tanks contained 11,000 cubic metres of a propane/butane mixture at the time of the accident. This volume of gas represented a third of the gas supply for the entire supply for Mexico City.
The Industrial Fire Disaster
On the 19th of November 1994, during transfer operations a gas leak developed, probably caused by a pipe rupturing during transfer operations. This caused a plume of LPG to concentrate at ground level for ten minutes. Eventually the gas cloud grew large enough for the wind to blow it towards the west end of the site where the waste-gas flare pit was situated.
At 5:40 a.m., on 19ty November 1994, the cloud of LPG vapor reached the flare and ignited resulting in a vapour cloud explosion that caused severe damage to the tank farm. The fire was fed from the leaking LPG pipe and within four minutes the first tank underwent a BLEVE. Despite attempts to control the fire, over the next twelve hours 12 separate BLEVEs occurred as more tanks blew up. The fire and smaller explosions continued until 10 a.m. the next morning after consuming 11000 cubic metres of gas. It is believed that the leak went undetected due to an ineffective gas detection system.
Casualties
The town of 40 000 residents surrounded the facility with a further 61 000 living in the hills around town. The explosions demolished houses and blew twisted metal fragments some with a mass of thirty tons over distances up to 1200 metres. The shock waves from the blasts destroyed and damaged houses and businesses up to 7 km away. Windows were shattered up to 10km away. Much of the town was destroyed by the explosions and ensuing fire, with the death toll between 500 and 600 people and between 5000 and 7000 serious injuries. Many bodies were incinerated to ashes in the heat and never recovered.
Industrial Fire Takeaway
Do you store flammable gasses and liquids in your operations? Are your detection systems operational with rosters for inspections in place? Is there sufficient firefighting equipment and proto teams trained? Do your sprinklers work? Do you have an evacuation plan? If you need a plan or advice or just want to make sure that you have done all you can to prevent tragedy, contact us at Firebrand for everything you need.