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equipment, so if one is the source of ignition, a primary explosion can easily travel along to damage the other processes.

4. Correct isolation of connected equipment If you fit an explosion vent to a dust collector, there must be isolation of the dirty inlet duct and isolation of the clean air outlet duct when it returns to the process area. This is vital because the explosion could propagate along these ducts causing other safety risks to people and equipment.

5. Errors with explosion vent installation If you’re going fit an explosion vent, make sure it’s done by a professional who will ensure it’s the correct size for your process requirements. Doing it on your own, and incorrectly, will create other health and safety risks: • Leakage of combustible materials from an incorrectly fitted vent results in burning materials being ejected at high pressure. This could discharge over a distance of 30 metres. • Always factor in any changes to the manufacturing process in relation to the size of vent required. If materials that you are processing have changed and have a higher KSt and PMax value, the force of explosive pressures may increase. • Vent ducting must be properly calculated and designed to strict guidelines so that the flame path can escape freely to a safe area. Correct size and length of ductwork is key to the efficient performance of a vent. • Be sure that your vent discharge path cannot possibly endanger nearby personnel. If a hazard exists due to explosion venting, then that area of risk must be clearly indicated with signage and cordoned off.

• Do not obstruct the explosion vent path. • Once your vent is correctly installed ensure it is regularly inspected.

6. Are your ducts and pipework safe? The strength of explosion vent ducts should be calculated so that they can withstand the maximum pressure of a vented explosion (Pred).

7. Inadequately protected Silos and Storage bins Vents should be placed on the top of the silo or on the sides at a height above the contained material. It is the most effective preventive measure for silos because of the potential explosive pressure that can build up inside them. • To ensure that your silos can withstand venting pressures, reduce the length to diameter ratio of the silo. Designing a larger diameter means that the vent area requirement will decrease significantly. Correct vent area sizing is critical so that the vent is large enough to prevent damage from explosive pressures. • Always test the material to be stored or handled and determine its KSt value. The KSt will inform the size of vent area required in your silo.

8. No electrical grounding and bonding Don’t encourage electrical sparking! Therefore, ensure that grounding wires are not broken or unconnected. Any piping with a flexible connection must be well bonded. This is particularly important when dealing with dusts that have a low MIE – it wouldn’t take much to cause a fire or explosion.

9. Bad housekeeping Even though cleaning up any accumulated dust may seem the obvious course of action to reduce dust explosion risk, it’s often overlooked. Dust accumulations in the ceiling spaces, beams and walls can fuel an explosion to the point of destroying a mill. Ensure your employees know where the dust accumulation ‘hot spots’ are and keep them clean. Do not use air sprays to remove dust, this just creates a dust cloud which is a secondary explosion risk waiting in the atmosphere.

10.Up to date risk management Your risk management strategy should include seeking advice from an explosion protection consultant. For example, if installation of safety equipment is not based on current, measurable data, your facility may be insufficiently protected. Similarly, review your combustible dust classifications (KSt and

Pmax levels) at regular intervals as process operations and materials change. This provision should be incorporated into Management of Change procedures.

For more information on BS&B Safety Systems explosion protection solutions visit:

Left: A flameless vent (R-IQR) FEED COMPOUNDER MARCH/APRIL 2017 PAGE 67

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