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.

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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