Smaller vent sizes for the same size vessel may be predicted in some cases. Explosion reliefs for small vessels There is no established size of vessel below which explosion reliefs are not required. In each case the consequences of an explosion need to be considered and Figure 1 sets out the factors to take into account. Longer ducts involving bends may still be effective provided they are within the detailed parameters described in Part 3 of the Institution of Chemical Engineers Guide 1 . Milling and grinding Feed stock must be treated by screening, de-stoning, pneumatic separation and magnets to remove foreign bodies before milling.
Hammer mills are usually strong enough to contain a dust explosion.
Some fires and minor explosions have occurred involving the pneumatic blower unit on the discharging vehicle. The problems appear to stem from product getting into the blower fan causing frictional heat or blinding of the clean air intake filter or both, resulting in ignition of filter material. It seems likely that non-return valves downstream of the blower are ineffective, particularly if the vehicle driver switches off the blower and relies on residual compressed air within the bulk tank to discharge the last remnant of product. This may cause products to enter the blower. Warn drivers of the danger and tell them to keep blowers going until discharge is fully complete.