www.truckandtrack.com Winter 21/22 Truck and Track 69 DANGEROUS GOODS Propane or Butane], or other volatile liquids such as alcohols, solvents, flammable resins et al; then the initial BLEVE tank rupture will result in a energetic and deadly fireball termed a Fuel-Air Explosion [FAE] or a Vapor Cloud Explosion [VCE]. For those interested in reaction dynamics, and how a superheated 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 [Boyles 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 embedded graphics. BLEVE’s of flammable gases/liquids, are where physical chemistry morphs into the reaction dynamics of an Exothermic Reaction [uncontrolled combustion] – fire and violent explosion. BLEVE’s can also occur with non-flammable liquids. Remember, the rupture of a container that is [or has become] overpressurised [from its SWP] results in an equalisation of pressure [container to surroundings, ratio]. 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° Celsius at atmospheric pressure, but imagine heating a pressurised water tank to 200° Celsius. The water inside would be prevented fromboiling due to the pressure buildup 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 depressurise [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/tanks of any liquid material, then the inadvertent super-heating of the liquid within the closed container [eg if a fire broke out on site and heated the tank/vessel in question], could result in a physical BLEVE. If the liquid however 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 Fuel-Air Explosion [FAE] aka a Vapor Cloud Explosion [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 [eg, 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 tanks/vessels to avoid damage or corrosion Van explodes propane cylinders BLEVE BLEVE Simulation. Photo © 2021 The Fire Service College, London Road, Moreton-in-Marsh, Gloucestershire GL56 ORH TRUCK & TRAILER SOLUTIONS WELCOME TO ALLPORTS GROUP allportsgroup.co.uk
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