Appendix 5A - Guarding of Machinery

Dangerous Machine Parts The major hazards of most mechanical equipment lie with their moving parts. Some examples of these hazardous moving parts include:

  • Revolving shafts, couplings, spindles, mandrels, bars and flywheels.
  • In-running nips between pairs of rotating parts.
  • In-running nips of the belt and pulley type.
  • Projections on revolving parts.
  • Discontinuous rotating parts.
  • Revolving beaters, spiked cylinders and revolving drums.
  • Revolving mixer arms in castings fitted with openings.
  • Revolving worms and spirals in casings fitted with openings.
  • Revolving high-speed cages in casings fitted with openings.
  • Revolving cutting tools.
  • Reciprocating cutting tools.
  • Reciprocating press tools and dies.
  • Reciprocating needles.
  • Closing nips between platen motions.
  • Projecting belt fasteners and fast running belts.
  • Nips between connecting rods or links, and rotating wheel cranks or dies.
  • Traps arising from the traversing carriages of self-acting machines.

Machine Guards

The most effective method of preventing machinery related accidents is to minimise the need for access to those dangerous parts. When this is not possible, another practicable way is to install proper guards around moving parts. The guarding of dangerous machineries is mandatory and is regulated by the Factories and Industrial Undertakings (Guarding and Operation of Machinery) Regulations.

Types of Guards

Dangerous parts of a machine can be guarded in a number of ways, the selection of which will depend upon the specific application. Some common ways of guarding the dangerous parts of machines include:

1. Fixed Guards

A fixed guard, by its design and construction, prevents access to the dangerous part(s) of a machine. Such a guard has no moving parts associated with nor is it dependent upon the machine on which it is fitted. A fixed guard is most suitable for guarding prime movers, transmission machinery and points of operation where manual feeding and withdrawal of materials are not necessary.

2. Adjustable Guards

An adjustable guard is comprised of a fixed guard with adjustable elements which the machine operator has to set into position to suit the operation. They are widely used on woodwork and toolroom machines. Where adjustable guards are used, the operators should be fully trained on how to make proper adjustments to obtain maximum protection.

3. Self-adjusting Guards

Self-adjusting guards prevent access to the danger except when the guard is forced open by the passage of the work. They usually incorporate a spring-loaded, pivoted element.

4. Interlocking Guards

Where guards need to be moved or opened frequently, it may be inconvenient to fix them on the machines. They can be interlocked mechanically, electrically or pneumatically to the machine controls. Interlocking guards are therefore suitable for guarding points of operation where feeding of material and withdrawing of components are required in every cycle of operation.
An interlocking guard should be designed to operate in such a manner that the machine on which it is installed cannot be operated unless the interlocking guard is in a closed position; and the guard cannot be opened unless the machine is not in motion or its removal from a closed position causes the machine to cease its motion at once. Interlocking guards should also be of the “fail safe? type, (i.e. if a component of the interlocking mechanism fails, the machine should not be capable of being set in motion).
Be advised that interlocking guards require a high degree of maintenance and a reliable system of regular testing and inspection.

5. Trip Guards

A trip guard is actually a device which ensures that an approach to a dangerous part beyond a safe limit stops or reverses the machine. Trip devices include trip bars and wires, photoelectric devices and pressure-sensitive strips and mats. It is critical that trip devices are properly adjusted and that the machine’s brake is in good order.

6. Two-hand Control Devices

Two-hand controls are used on machines with cyclic operations where the work is placed in the machine and the machine struck on. They are applicable only to machines with a single operator and the control buttons must be positioned more than a hand-span apart. The control circuit should be arranged so that both controls must be activated simultaneously to start the cycle and that both controls must be released after each cycle before the next cycle can be initiated. Release of either button during the dangerous part of the cycle must stop or reverse the machine movement.

7. Automatic Guards

This type of guard closes automatically when the machine cycle is initiated and is arranged so that the machine will not move until the guard is in the safe position. A version of this type of guard moves across the work area as the machine operation is initiated, preventing any contact with the machine in the area. This type is sometimes known as a “sweep-away? guard.

Construction of Guards

Guards must be rigid and of substantial construction, and be made with incombustible materials. Wherever practicable, guards should be made from solid material in preference to perforated or open mesh construction. If sheet steel is used, the minimum thickness should be 18 s.w.g. (or 1.2 mm). Where open mesh guarding is chosen, the apertures should be such that finger access to the dangerous parts is not possible. Wing nuts or similar fasteners should not be used to secure various sections of the guards because they can be easily removed. The sections should be bolted or riveted as far as possible.

Maintenance of Guards

Regular and frequent checks of machine guards should be conducted to ensure that they are in a good state of repair and are kept in position. All interlocking guards, automatic guards, trip guards and two-hand control devices should be regularly inspected and tested by a responsible and competent person, and a record kept of the results and any action(s) taken.