Industrial Explosion FAQ's

Explosion protection measures are collectively the means by which we reduce the risk of ignitions that can give rise to deflagrating explosions that are liable to have harmful, disruptive and/or costly consequences, AND mitigate against these explosion consequences. Explosion protection measures include:

• Explosion prevention – by ignition prevention and/or process controls;
• Explosion containment – where, we rely on pressure resistant construction to ensure that there is no consequential blast, external flame escape and equipment deformation/rupture arising from an ignition in the process equipment;
• Explosion venting – where by design we take measures to relieve the explosion over-pressure so as to mitigate against risk of incurring constructional pressure damages and/or uncontrolled flame/blast escape;
• Explosion suppression – where by design we detect and suppress an explosion before it builds up damaging or destructive pressures within the process, and then suppress residual explosion combustion;
• Explosion isolation – where by design we seek to minimize the possibility of flame/explosion propagation to other connected process equipment;
• Advanced inerting – where by design we deploy an inerting concentration of gaseous or powder extinguishant before flame arrival at the protected location.

The most extreme outcome of any ignition and consequent explosion within processing equipment arises when there is an unintended loss of containment of the primary explosion – the impact of blast and flame expansion into the plant complex or building can cause dust layers etc. to become launched into an explosible dust cloud – giving rise to a much larger volume secondary explosion within the plant complex or building confines. This risks catastrophic damages and consequences. Secondary explosions are an attendant risk in all processes where dust can be launched into the air and effective primary explosion protection is not deployed.

A deflagrating explosion can transition to a detonation, where the flame front is driven on the shock wave, if certain pre-compression conditions are met (typically the consequence of flame accelerations in long unprotected pipelines and ducting). A primary objective of IEP Technologies’ industrial explosion protection system design will be to minimise risk of any such regression to detonation by appropriate constructional explosion protection measures.

All combustible dusts are liable to form explosible dust clouds if the dust concentration can exceed a certain minimum dust concentration known as the Lower Explosion Limit (LEL). If in doubt a representative product sample should be submitted for laboratory tests to establish if it is explosible, and to quantify it’s ignitability, explosibility and Lower Explosion Limit.

Sometimes – provided that there is a sufficient margin of safety between the maximum operating concentration and the LEL concentration, AND also provided that the risk of an unintended mechanical disruption or other failure mechanism that could give rise to the formation of an explosible dust cloud is acceptably low. The LEL concentration is process material specific (typical values are in the range 10-100 g/m3) and is further reduced in the presence of very small concentrations of any flammable vapour. In industrial practice it is more often the case that reliance cannot be placed on this as the primary explosion safety measure.

While it is sound engineering practice to attempt to minimize ignition sources, it is not possible to eliminate all ignition sources from standard and/or upset operating conditions. The first step in reducing the likelihood of an ignition source is to have the material being processed evaluated for the minimum ignition energy (MIE). The MIE of the product will determine if the more frequently encountered/anticipated ignition sources (frictional heating, mechanical sparking, static discharge etc) pose an ignition risk and if other ignition risks (lightning strike, electrical arcing, smouldering combustion, external fires etc) should be addressed. The MIE is process material specific, and is lowered to a few millijoules in the presence of very small concentrations of any flammable gas/vapour. The Combustion Research Center can provide details on MIE testing.

An explosion is liable to propagate along interconnections between protected vessels. Such explosion propagation is likely to give rise to an enhanced (more intense) explosion in the connected vessel than would be expected from a simple ignition in that vessel, because of pressure piling, induced turbulence and flame jet ignition effects. These explosion enhancements can compromise the efficacy of the installed explosion protection on the connected vessel, unless they have been allowed for as part of the vessel IEP design. Explosion isolation is a proven method of reducing the risk of such enhanced explosions, and may be an essential requirement to attain a sufficient risk reduction from the overall explosion protection system.

It is recommended to consider the features of each. The practicality, efficacy and risk reduction benefit of the selected option should be taken into account;
– The area to safely vent an explosion (as a rule of thumb the vented fireball size is likely to be about eight times the volume of the vessel being vented),
– The toxicity or contaminative impact of a vented discharge,
– The consequence and mitigation requirements of any post explosion fire in the vessel,
– The refurbishment time following a protected explosion incident and the additional demand (if any) on the fire and explosion protection of any connection and upstream/downstream connected vessels combine with commercial factors of cost, longevity and convenience to assist the decision.

Since the metrics of explosion protection are a function of the explosibility characteristics of the specified process material, any change in process material is likely to impact the efficacy of the installed explosion protection measures. Where processes are expected to handle a range of materials it is important to specify both the most ignitable and the most explosible materials at the design stage. Some operators prefer to just specify an explosion class – e.g. ST1 Limit organic dust – and of course the determined explosion protection system metrics relate to that limit material. Improved risk reduction factors can prevail when less explosible materials are processed in the operational practice.

In cases where a more explosible material, or a material of a different class such as a hybrid gas/dust, is intended a full review with possible upgrade of the protection system will be necessary.

Sometimes – it depends on the fire load and the shut down facilities of the protected process. Where a post explosion sustained fire fed by air ingress is probable, for example in a vented bag filter, it is normally recommended to integrate post explosion fire protection as part of the overall explosion protection measures. A key design intent of IEP Technologies will normally be to mitigate explosions, shut down the process and control any post explosion fires such that risks of a subsequent re-ignition from the primary event are minimised.

Where external fires, or fires not connected to the primary explosion occurrence are an attendant risk, additional measures may be necessary – including a need to consider the safety of fire fighters.

IEP Technologies will specify a recommended maintenance frequency, which is likely to be dependent on the protection hardware specified, its duty cycle and the operating environment that the system is exposed to. Note that any reduction in maintenance frequency will de facto reduce the intended risk reduction factor of the installed explosion protection system.

Explosion protection systems need to checked and maintained in accordance with IEP Technologies recommendations to sustain their quoted performance metrics. This maintenance will include the scheduled replacement of all life expired component parts of the system and compliance testing/recertification of hardware such as pressure vessels. Provided that the system is maintained as specified IEP Technologies will not normally impose a lifetime limit on the system – recognising that in practice a system, or component part thereof, may become obsolete or non-compliant with up-issued code or otherwise beyond economic repair.