The hidden danger
Whilst not strictly part of the fan supply, and therefore not suggesting any specific ancillaries, there are what might be termed the “hidden clangers” of fan systems. The following features which may be necessary in the ductwork system are suggested:
• As well as the normal dangers of rotating machinery, some fans (e. g. paddle-bladed), present an additional hazard in their ability to suck in loose material as well as air. Solid objects can pass through the fan and be discharged by the impeller as potentially dangerous projectiles. They can cause serious damage to the fan itself, if not allowed for in the design.
• Intakes to ductwork should whenever possible be screened to prevent the accidental or deliberate entrance of solid objects. For example, on a sawdust handling system an intake screen should be provided which will allow the entry of sawdust but prevent the entry of large pieces of wood.
Figure 16.7 Access door in duct and specimen intake screen
Figure 16.9 Fan set on sheet steel fabricated baseframe
Access doors to a duct system should never be opened with the fan running.
• On the downstream (or pressure) side of the system, releasing the door with the system in operation could result in explosive opening. On the upstream (or suction) side the inflow may be sufficient to suck in tools and clothing, etc, and even cause a man to lose his balance. Where quick-release handles are provided on access doors, at least one positive bolt should be installed to prevent accidental opening.
• When a fan is being started for the first time, a complete inspection should be made of all the ductwork and the fan interior to make certain that no foreign materials have been left, which could be sucked into or blown through the ductwork, (see Figure 16.7).
Posted in Fans Ventilation A Practical Guide