Making the fan system safe
Improper installation, use or maintenance can make fan units a danger. The following Sections are intended to assist in the safe installation and use of fans and to inform operating and maintenance personnel of the dangers inherent in all rotating machinery and especially those used in air or gas movement. Often only the fan is supplied by a manufacturer.
The customer/user must therefore consider how the rest of the system — motors, drives, starters, etc, may affect fan operation.
Installation and maintenance must be carried out by experienced and trained persons, as discussed in Chapter 18. As well as the manufacturer’s own instructions, it is important that all national and local government requirements are complied with.
In the United Kingdom, the Health and Safety at Work Act 1974 should be followed.
All fans have moving parts which may require guarding. It is a fact of life that two danger areas are the fan inlet and outlet. Perfect guarding would require these to be blanked off completely — but then there would be no air/gas flow. Fan guards have to be designed to reduce the fan’s performance as little as possible whilst giving a good measure of safety. This requires that they do not deflect when leant against.
In areas accessible only to experienced and trained personnel, a standard industrial-type guard may be adequate. This will prevent the entry of thrown or dropped objects with the minimum restriction of airflow.
Where the fan is accessible to untrained personnel or the general public maximum safety guards should be used, even for DIDW fans, at the cost of some loss of performance. Fans located less than 2 metres above the floor require special consideration. Even roof-mounted equipment will require guards when access is possible, for example, by climbing children.
For full information on this subject the customer/user should refer to ISO 12499 and AMCA410.
16.2.1.1 Inlet and outlet guards
These are not necessary for an Installation Category D fan, provided that access to the ducting cannot be made whilst the fan is in operation (Figure 16.2). With the same proviso, an inlet
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Figure 16.2 Fan protected by ductwork |
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Figure 16.1 Ancillaries available with centrifugal fans
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Figure 16.5 Typical example of an Arrangement 1 (belt driven) fan. (A combined guard covering the bearings and shaft, and cooling disc if fitted, should be provided.) |
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* Important: Partial guards should only be used where restricted access makes the use of a full guard impossible, and never unless the partial guard can be combined with existing stationary structure to form a complete guard. |
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Figure 16.3 Inlet and outlet guards (Installation Category A) |
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Figure 16.4 Ducting at outlet, guard at inlet (Installation Category C) |
Guard must be provided for a Category A or B fan whilst an outlet guard must be provided for a Category A or C fan.
The intention with all inlet or outlet guards is to prevent finger or arm contact with the internal moving parts. The distance from the guard to the moving part will determine the mesh size. Thus a backward bladed centrifugal fan, which has a relatively long inlet cone, can have an inlet guard with a more open mesh than say an axial flow fan, where the guard is closerto the impeller.
The illustrations Figures 16.2 to 16.4 are self-explanatory. The customer should advise the manufacturer how the fan is to be installed and the guards which he requires.
Fans may be driven directly from the motor shaft or through a belt drive. In every case where the bearing assembly, rotating shaft, sheaves, or belts are exposed, a suitable guard should be provided, (see Figures 16.5 and 16.6). Most centrifugal fan manufacturers include a combined shaft (and cooling disc if fitted) guard as standard, but it is as well to check.
Customers often prefer to provide their own motors, drives, and drive guards on indirect driven fans. They should in all cases follow the recommendations of BS 5304:1975 and BS 3042:1992, or other relevant local standards.
In restricted access areas, one-sided guards of expanded metal may be acceptable. Readily accessible locations will require maximum protection guards, and in many cases a fully enclosed sheet metal guard. The loss of fan performance on DIDW fans must be weighed against the degree of safety provided. Where the customer/user is in any doubt, he should purchase the complete assembly of fan, drive, motor, guarding, and combination baseplate from the fan manufacturer who can provide a fully engineered system to meet any specified standards. For indoor applications a wire mesh drive guard will be perfectly satisfactory, but for outdoor applications, a totally enclosed weatherproof driveguard will be necessary, probably manufactured from sheet steel.
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Figure 16.6 Typical example of an Arrangement 8 (coupling drive) fan. (A combined guard covering the cooling disc, bearings and shaft should be provided.) |
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