This feature provides readers with an insight into one of the most troubling incidents, the much-feared Boiling Liquid Expanding Vapour Explosion (BLEVE) that can occur in the Dangerous Goods Supply Chain, but most crucially how to avoid the horror of a BLEVE as well as the associated risk of a Fuel-Air Explosion (FAE) aka a Vapour Cloud Explosion (VCE) occurring mere milli-seconds after the BLEVE has breached the pressure vessel and the conditions of a thermal runaway reaction have been initiated.
It was a horrific BLEVE and subsequent FAE/VCE incident in Spain in 1978 that initiated the tightening of the regulations on the carriage of dangerous goods by road throughout Europe – namely the Los Alfaques Disaster.
The Los Alfaques disaster occurred at a campsite in Spain on 11 July 1978, where a road tanker carrying 23T of liquefied propylene caught fire and exploded adjacent to the Los Alfaques Campsite. The fireball caused extensive damage and mass casualties including 217 deaths and over 200 injuries.
The aftermath of this disaster resulted in the UK’s Dangerous Substances (Conveyance by Road in Road Tankers and Tank Containers) Regulations, trivially termed the Road Tanker Regulations (RTR) taking priority over the Classification, Labelling and Packaging of Dangerous Substances Regulations (CPR) and the Dangerous Substances (Conveyance by Road in Packages) Regulations (PGR). These, among other regulations on the carriage of dangerous goods, would eventually become consolidated throughout Europe as ADR (Accord Dangereuse Routiers). Despite Brexit, UK domestic regulations run in concert with mainland Europe and Ireland under the ADR framework.
But first some context
A little while back, my friend the Belfast based novelist and leading lawyer Stephen Mearns (who writes as Steve Cavanagh) contacted me, regarding his sixth Eddie Flynn thriller. He required a plot device related to industrial chemistry.
I came up with a scenario related to a BLEVE. Steve used it in The Devil’s Advocate, which became a bestseller in The Sunday Times / A C Nielsen UK book-charts on release in 2021; incidentally it came out in paperback in January 2022.
Due to my industrial experience of handling liquids and gases (in pressurised containment, tanks, cylinders and in transit) and an academic understanding of reaction mathematics and dynamics, especially of the exothermic variety; I thought it might be useful to explain what a BLEVE (and the associated FAE/VCE) incident really is, and how one can avoid the risks that bring about this sequence of deadly events.
I first encountered a BLEVE, on a small scale at the Fire Training (now called Fire Services) College in Gloucestershire in the 1980s. I was sent for training when I worked on a petroleum pipeline and storage facility outside of London, as part of the emergency team. The BLEVE was simulated using liquefied propane in a pressurised gas cylinder, heated vigorously until the liquid propane boiled resulting in a BLEVE, which the trainers put out using abatement foam. The training helped me in my career working in production, storage and transportation of dangerous goods, especially in the Middle East, on gas platforms for liquified petroleum gas (LPG) and liquified natural gas (LNG). I would recommend anyone working with these products, or any dangerous goods that require containment in closed vessels, attend one of the many courses run at Moreton in Marsh’s Fire Services College.
The mathematics, physics and chemistry of a BLEVE
A boiling liquid expanding vapour explosion is caused by the rupture of a vessel, which could be a holding tank, road tanker, rail car or even a pressurised gas/liquid cylinder that contains a liquid under pressure that has reached, or exceeded, its atmospheric boiling point.
The contents of the pressurized vessel can only remain liquid as long as the vessel is intact. If the vessel’s integrity is compromised, the loss of pressure and subsequent rapid reduction of boiling point of the super-hot liquid can, by pressure equalisation with atmosphere, cause the liquid to rapidly convert to gas and expand with exponential and violent rapidity. If the gas is combustible such as a hydrocarbon (e.g. propane or butane) or other volatile liquids such as alcohols, solvents, flammable resins et al. then the initial BLEVE tank rupture will result in an energetic and deadly fireball termed a Fuel-Air Explosion (FAE) or a Vapour Cloud Explosion (VCE).
Those interested in reaction dynamics, and how a super-heated flammable liquid in a pressurised container can boil with an explosive phase change (liquid to gas) by the ruptured vessel, should look into the physical chemistry of the gas laws (Boyle and Charles) as well as the thermodynamics of an exothermic reaction from the Arrhenius equation. This calculates the rate of a reaction by understanding the effect of temperature on the kinetics of the reaction. This equation was proposed in 1889 by Svante Arrheniu and takes into account the activation energy required to initiate the explosion. This is detailed in the graphics.
BLEVEs of flammable gases/liquids are where physical chemistry morphs into the reaction dynamics of an exothermic reaction (uncontrolled combustion) – fire and violent explosion.
BLEVEs can also occur with non-flammable liquids. Remember, the rupture of a container that has become over-pressurised (from its SWP) results in an equalisation of pressure (container to surroundings). This causes an aggressively sudden lowering of the boiling point of the pressurised liquid, due to tank rupture (pressure equalisation with surroundings), resulting in a violent explosion, if not also a fire. Examples of non-flammable BLEVEs include water boiler tanks, cryogenic material (subject to vacuum insulation failure), which become over-heated and rupture.
Water boils at 100°C at atmospheric pressure, but imagine heating a pressurised water tank to 200°C. The water inside would be prevented from boiling due to the pressure build-up inside the tank which could exceed the safe working pressure (rating) of the said vessel. This could lead to tank rupture, which will cause the water pressure inside the vessel to rapidly de-pressurise as the tank equalises with atmospheric pressure. This reduces the boiling point of the liquid in milliseconds, and there will be a subsequent violent explosion as the liquid turns to gas. Though water is not flammable, the physical violence of the explosion would be dangerous and could initiate a fire in adjacent areas if flammable material is stored (flash point/friction/electrical considerations).
Remember, even if your site has closed vessels of any liquid material, then the inadvertent super-heating of the liquid within the closed container (e.g. if a fire broke out on site and heated the vessel in question), could result in a physical BLEVE. However, if the liquid is flammable, then beyond the physical BLEVE, the mathematics of Boyle, Charles and Arrheniu come into play and the BLEVE could undergo an exothermic reaction, resulting in a FAE aka VCE.
With a BLEVE, either of a flammable or non-flammable material, contained in a closed vessel, the rupture and subsequent damage could also result in toxic fumes being evolved, especially in a fire situation.
What to do?
In order to minimise the risks of a BLEVE of containment (temp/pressure) vessels, be they for flammable or non-flammable liquids under pressure, the following considerations need to be factored in:
- Training of staff
- Running drills
- Counter-measures, e.g. fire protection, foam, trained staff, safety plan, wind-socks, plume detection et al.
- Fire Risk Assessments as well as Operational Risk Assessments (of SOPs*)
- Ensuring there are engineering ‘change control’ processes in place
- Thermal and pressure sensors / warning alarms on pressure vessels (SWP* or SWT* if exceeded)
- Documented maintenance of pressure vessels to avoid damage or corrosion
- Periodic and systematic inspection of pressure vessels
- Pressure relief valves / reseating of valves once SWP* restored
- Bursting Discs to operate if SWP* of non-flammable containment vessel is exceeded significantly
- Thermal barriers
- Water spray cooling systems
*SWP = Safe Working Pressure
*SWT = Safe Working Temperature
*SOP = Standard Operating Procedure
This article is written in good faith and is not comprehensive, or site/situation specific but provided for insight only.
The following selected examples of BLEVE incidents are worth putting into a search engine to understand the significance of this type of dangerous goods incident:
- June 1959: Meldrim Trestle Disaster, Georgia USA.
- August 1959: 100,000-litre gasoline tank rupture, Kansas, USA.
- March 1960: Whisky bond fire, Glasgow, Scotland.
- January 1966: LPG storage tank rupture, Feyzin, France.
- June 1970: Derailed propane railcar explosion, Illinois USA.
- July 1973: Explosion of propane tanker, Kingman, Arizona.
- January 1978: LN2 (liquid nitrogen) tank rupture, West Virginia, USA.
- February 1978: LPG rail tank-car derailment/explosion, Tennessee, USA.
- July 1978: Liquefied propylene tanker explosion (Los Alfaques), Alcanar, Spain.
- November 1984: Liquefied petroleum gas (LPG) tank farm, Mexico City, Mexico.
- December 1988: Propane Tanker rupture, Memphis, USA.
- April 1990: LPG fuel tanker & Tank Farm explosion, Sydney, Australia.
- April 1998: Propane Tank Explosion, Iowa, USA.
- May 1999: Propane tanker explosion, Vourla, Greece.
- August 2008: Propane storage facility explosion, Ontario, Canada.
- June 2009: LPG tanks on train derailment, Viareggio, Italy.
- March 2015: MRI machine, liquid helium, BLEVE, New Jersey, USA
- April 2017: Tank Farm and Pipeline BLEVE, St Louis, Missouri
- August 2018: LPG tanker explosion, Bologna, Italy.
- March 2019: BLEVE (no further info available), Yancheng, Jiangsu, China.
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