A guard or fence is only effective if it is constructed to prevent a person from reaching the danger or nip point. A person is capable of reaching upwards, over, into, around or through a guard or fence, and all these aspects must be taken into account when considering the effectiveness of a guard or fence.

For conveyor belt installations the so-called 'nip guard', examples of which are shown in the sketch below, extend over the whole width of the pulley and are regarded as a reasonable solution to prevent access to the danger points. Installation of this type of guard is strongly recommended but unfortunately it is impossible to install it in such a way that a person is completely prevented from reaching around it. A nip guard alone cannot therefore be regarded as sufficient protection and it is essential that pulleys are further guarded or fenced off to meet the requirements of the regulations.

The following may be provisionally accepted as safe in the absence of facts to the contrary:

Upwards

Any pulley or idler, which is 3,5 metres or more in height and therefore beyond an upward reach, may be regarded as being positionally safe and need not be guarded.

The possible reduction of this safe clearance by a build-up of spillage or discharge of material should, however, be borne in mind.

Over

Head and tail pulleys must be guarded on at least the two sides and the top unless the guards or fences on the sides are extended to a height that makes it impossible to reach over and contact the nip point.

If side guards are only attached with a very small clearance between the edge of the belt and the side guard, this may perhaps be regarded as adequate to prevent reach over the guard to the nip point, but will not necessarily prevent tools or clothing from being caught in the nip point.

If a top guard is attached it must be high enough above the belt to ensure that the load on the belt will not damage it.

Into

The distance that the guard or fence is placed from the side of the belt determines the distance that these extend away from the nip point along the length of the belt. An acceptable distance is at least 0,85 metres away from the nip point, preferably from the position of the nip guard.

Around

This is similar to 'into' so far as the conveyor pulley guard is concerned, but may also be applied to determine the length of the top section of the guard. The same minimum distance of 0,85 metres applies.

When a V-belt or chain drive is associated with the conveyor installation, a common point of error is that while the V-belts or chains are perfectly guarded around the perimeter and on one side, the guard is installed in such a way that the nip points can easily be touched by reaching around the section forming the perimeter guard.

Through

The protection afforded against injury by reaching through the guard is determined by the shape and size of openings in the material used for construction of the guard or fence.

Square Openings:

It may be assumed that there is no reach through an opening of 10 mm x 10 mm or less, as it is too small for fingers. If the opening is such that it will admit one, two or three fingers, the reach is restricted by the roots of the fingers, a distance normally not exceeding 100 mm.

When the opening is sufficient to admit the whole arm and a small portion of the shoulder, the reasonable safe distance is based on the distance from the fingertips to the armpit, which is assumed to be 0,85 metres.

Screening materials with openings in excess of 80 mm x 80 mm shall not be used in the construction of guards or fences. Preference shall be given to materials with openings not exceeding 25 mm x 25 mm.

Elongated Openings (openings with parallel sides):

Openings up to 6 mm wide are of no consequence. The guard or fence so constructed may virtually be regarded as a sheet, and a working clearance of approximately 25 mm is all that is required.

Openings greater than 6 mm but less than 13 mm will admit part of a finger and require at least 50 mm clearance from danger points.

Openings in excess of 13 mm but not greater than 80 mm are subject to the following formula:

Y = width of opening in millimetres