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This circular draws attention to the potentially high risks posed by accessible nip points at conventional conveyor idlers on heavy-duty belt conveyors

1. The mining industry is already aware of the potential dangers arising from ‘nip hazards’ on belt conveyor systems and over the last twenty years a policy has evolved of nip point guarding the main system rollers on belt conveyors. These include the drive rollers, delivery rollers, return rollers, loop rollers, and deflection rollers. The process has been a progressive one, usually in response to an accident resulting from ineffective peripheral guarding. The success of adopting nip point guarding at these vulnerable points on the system is demonstrated by the fact that the numbers of nip point accidents have reduced where they have been provided.

2. In addition to the above mentioned main system rollers, nip points also exist at every supporting idler roller. The risk of serious injury posed by these has however been regarded as quite low and accident experience has supported this view. This perceived low risk and the practical difficulty of effectively guarding every idler roller nip point on a conveyor system, has led to an industry wide toleration of unguarded idler roller nip points, except for certain places where idler roller guarding has traditionally been provided.

3. These exceptions are usually found where the nip force and risk of serious injury is higher than that normally encountered, e.g. where there is increased pressure between idler rollers and the belt, or where there is an increased likelihood of persons making inadvertent contact with the nip point. Hence it has become common practice to guard idler rollers at:

· anti-clines and changes of gradient, where the idlers are more heavily loaded than normal

· anti-spillage skirts at loading points, where the conveyor belt may be held down against the idlers by the skirt plates

· under-passes, materials storage areas and maintenance points under conveyors, where the probability of persons making contact with a rotating bottom idler may be high.

4. At such locations, peripheral guards, or nip point guards, have normally been provided to address the increased risk. The decision as to which type to use has depended on site-specific practicalities and overall effectiveness.

5. Over the past five to ten years, the size of conveyor systems used in the deep coal mining industry has increased significantly. Whereas previously, the average drive power of a conveyor ranged from 60kW (80hp) to 180kW (240hp), it is now commonly 450kW (600hp) to 750kW (1000hp). Other changes include:

· The conveyor belt has increased in size and weight, typically from 0.9m wide type 6 belt, to 1.2m wide type 8 belt and larger.

· The belt weight and mineral load per unit length has increased, while idler roller spacing has remained the same.

6. These changes have led to an increase in the nip point force on heavy-duty conveyor top and bottom idler rollers and the greater width of idler rollers, particularly bottom idler rollers, has increased the general accessibility of nip points.

7. The net result is that there is now a significant increase in the risk of injury posed by heavy-duty conveyor idler rollers. This coupled with the industry’s reliance on out-dated prescriptive requirements for guarding, is leading to situations where high risk nip points are not being appreciated, identified and adequately addressed.

8. Several accidents have occurred on heavy duty conveyor belt idler rollers, indicating the need to examine:

· Places where access is needed for maintenance purposes, particularly in front of drives, or behind loops in the conveyor belt;

· Underneath raised conveyors, where materials and tools, or other equipment are often stored;

· Underneath raised conveyors where dinting, or cleaning operations need to be performed;

· In-line bottom belt man-riding boarding platforms, where persons using the platform may make inadvertent contact with a top belt idler roller above them;

· Conveyor bridges between the bottom and top strands of a conveyor, where persons may make contact with a top belt idler roller;

· Fines conveyors, under the bottom strand of a heavy-duty conveyor, where persons carrying out maintenance may make contact a bottom belt idler roller.

This will be determined largely by the pressure between the belt and the idler roller. For example, if the stationary conveyor belt cannot be lifted off the idler by a person using one hand, it is likely that the control measures described in Paragraphs 10 - 12 below will need to be applied.

This will be determined by the height of the nip in relation to the activities that could be performed at that location, also, the separating distance between the nip point and the likely position of employees that might make contact with it.

10. The control measures applied to prevent injury to persons will need to be appropriate for the risk and follow the hierarchical approach described in Regulation 4 of The Management of Health and Safety at Work Regulations 1999 and Regulation 11 of The Provision and Use of Work Equipment Regulations 1998. These can be summarized as:

· Where elimination is not possible, employees should be prevented from gaining access, by effective guarding, (which might be a temporary guard fitted only for the duration of the task in hand), or where this is not practicable, by clear instruction, training, supervision and education to enhance hazard awareness and knowledge of safe working procedures.

11. Where it is necessary for employees to work close to unguarded nips, the work should be controlled by a permit to work system in compliance with the requirements of Regulation 6 and Schedule 1 Part 1 of The Mines Miscellaneous Health and Safety Provisions Regulations 1995. This should ensure that the control measures necessary for a safe system of work are in place.

12. The permit to work system should require appropriate measures to be taken to ensure that the conveyor is stationary and cannot restart or move, by any means, while employees are at risk. This will usually require the conveyor’s driving power to be isolated and securely locked off.

For further information, please contact LD5 (Mines Inspectorate), Edgar Allen House, 241 Glossop Road, Sheffield, S10 2GW. Telephone 0114 291 2390

Note: where there is a likelihood of a peripheral guard being removed for cleaning or maintenance purposes, a nip guard should be provided, where a rotational hazard exists in addition to the nip hazard, a nip guard and peripheral guard should be provided.

MEMORANDUM ON GUARDING OF BELT CONVEYORS

During 1981 most fatal accidents at mines and works as well as other accidents resulting in serious injury to persons, in which machinery was directly involved, occurred on belt conveyer installations. These accidents normally took place basically because the danger points of the belt installation were either unguarded or inadequately guarded, although it is admitted that the ingle cause analysis of an accident is probably an unwarranted simplification of a complex problem.

Mines and Works Regulation 20.5 decrees that all exposed machinery which, when in motion, may be dangerous to any person shall be securely fenced off. Efficient guards shall be provided to such parts of any machinery as may be a source of danger to any person.

The wording “may be dangerous to any person” and “may be a source of danger to any person” clearly implies that at places where persons may reasonably be expected to work or move about machinery must be guarded or fenced off. It does not matter whether a person has or has not any right to approach such items of machinery, for should an accident result, the plea of safety by position will not normally be accepted in law unless t least certain minimum requirements were complied with. Also implicit in the statutory requirements is the fact that it is not sufficient to act with hindsight but, as far as is humanly possible hazards must be identified before danger arises. Guards or fences must therefore be constructed to protect against unforeseen contingencies, not merely against normally expected operational hazards.

Most of the accidents at belt conveyor installations, during the past year, occurred when part of the victim’s body, clothing or tools became trapped at the nip point where the belt passed around a head, tail or snub pulley. In one accident a person was fatally injured when part of his body was pulled in between the conveyor belt and a return idler.

For a guard or fence to be effective it must be so constructed that a person is prevented from reaching the danger nip point. A person may normally be regarded as capable of reaching upwards, over, into, around or through a guard or fence and all five these aspects must be taken into account when considering the effectiveness of a guard or fence.

For belt conveyor installations the so called “nip-guard”, examples of which are shown in the attached sketch, extending over the whole width of the pulley may be 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 by itself cannot therefore be regarded as sufficient protection and it is essential that pulleys should be further guarded or fenced off to meet the requirements or the regulations.

With regard to belt conveyor installations an das far as the five aspects of “reaching” previously referred to are concerned the followin9 may be provisionally accepted as safe in the absence of facts to the contrary:

(ii) Upwards:

Any pulley or idler which is 2,5m or more beyond an upward reach may be regarded as positionally safe and need not be guarded. Possible reduction of this safe clearance by a build-up of spillage or discharge of materials must be considered.

(iii) 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 carried to such a height that it is impossible to reach over it and contact the nip-point, If side guards only are provided with a very small clearance between the edge of the belt and the side guard this may perhaps be regarded as adequate for preventing reach over the guard to the nip point but this will not necessarily prevent tools or clothing from being caught in the nip point. If a top guard is provided it must be high enough above the belt to ensure that it will not be damaged by the load on the belt. Tail pulleys normally also require the guard to be closed at the rear.

(iv) Into:

The distance that the guard or fence is away from the side of the belt will really determine the distance that the guard or fence must be extended away from the nip point along this length of the belt. It is normal to make this distance at least O,85m away from the nip point or preferably from the position of the nip-guard.

(v) Around:

This really has the same meaning as ‘into” as 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 O,85m shall apply as well for this dim~nsion.

If there is a V-belt or chain-drive associated with the conveyor installation a very common defect is often found here where the V-belt or chain are perfectly guarded around the perimeter and on one side, but the guard is so installed that the nip points can easily be contacted by reaching around the section forming the perimeter guard.

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

It may be assumed that there is no reach through in opening of 10mm x 10mm or less as fingers cannot normally be admitted. It 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 100mm. When the openings is sufficient to admit the whole arm and the small portion of the shoulder the reasonable safe distance is based on the distance from the fingertips to the armpit, which may be assumed to be 0,85m.

Screening material with openings in excess of 80 mm x 80 mm should not be used in the construction of guards of fences. Preference should be given to materials with openings no exceeding 25 mm x 25 mm.

(a) Openings up to 6 mm wide may be disregarded. 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.

(b) Opening grater than 6 mm but less than 13 mm will admit part of a finger and requires at least 50 mm clearance from danger points.

X = 1OY where X = reasonable safe distance from danger point in mm. Y = width of opening in mm.

Although it was stated that it is essential that head, tail and snub pulleys of belt conveyor installations, which are “within reach”, should be guarded, accidents have happened on carrying idlers. The outcome has frequently been serious particularly where the amount the belt can lift off the idler is restricted. The danger at idlers is even more so when fixed hoppers or skirt plates, under which the hand can be trapped, are fitted directly above the idlers. If this is the case the danger points must be very carefully guarded or completely enclosed. This also applies, even more so, to belts on which hand-sorting is performed.

On belt conveyors the return belt or idlers may also present a hazard especially if specific places exist where persons regularly pass through underneath the belt. As such places it is recommended that the underside should be guarded and crossing at other places should be discouraged or prevented, even if only two or three stands or 8 gauge galvanized wire are used along the outside of the support in framework to achieve his purpose.

Driving belts, chains and couplings between driving motors and gearboxes or drive pulleys must be effectively guarded. Experience has shown that even when transmissions are. Apparently inaccessible they can still be a hazard. If the driving mechanism or any other part is fenced off completely in such a way that access thereto can only be obtained through a gate or door forming part of the fencing then this gate or door should be interlocked so that the conveyor is stopped when this gate or door is opened.

When faults, accidents or blockages occur, it is normally necessary to bring the conveyor to an immediate halt. A continuous “trip-wire” stretching the whole length or the conveyor arranged, if pulled, to actuate the stop-switch of the conveyor, is an effective and essential safety device. With such a facility available the operator will be less tempted to try and rectify faults with the conveyor running.

It must however stretch the full length of the conveyor even to the inside of the guarded sections. If the belt conveyor is so installed that persons can walk along the conveyor on either side of it then “a trip-wire” must be installed on both sides of the conveyor. It is also recommended that a “lock-out” facility be provided on this trip wire arrangement.

Lateral movement of the belt is usually caused by a build-up of material on the head and tail pulleys, the carrying idlers or snub pulleys. The manual removal of “build-up” is slow and complicated, and more often than not dangerous. In order to keep the pulleys and rollers clean suitable mechanical devices must be installed. The manual removal of “build-up” should not be permitted whilst the belt conveyor is in motion.

It is of ten necessary for an attendant to cross a conveyor at various points, It is dangerous to climb onto the moving belt. Where it is impossible to establish safe passageways underneath the belt, cross-over bridges with hand rails, must be provided. The position of the bridges will depend on conditions at the belt conveyor installation but, unless a sufficient number is installed they will not always be used. Access to the cross-over bridge must be provided by stairs equipped with handrails. Vertical ladders should be avoided. The cross-over bridge should also be equipped with a “toe-board” and an intermediate or knee rail.

Safety at belt conveyor installations may be further enhanced by creating the optimum working environment including not only adequate ventilation, illumination and absence of undue noise, but also sufficient clearance around the installations and along walkways. Walkways should have even non-slip surface, be properly drained and fee from obstructions.

Idler Roller Nip Hazards On Heavy Duty Belt Conveyors

Issue Date : 31st December 2002 Review Date : 1st January 2005

(SPC/TECH/LD5/05)