A User's Guide to Conveyor Belt Safety
Contents
1. Upper and Lower Strands in a Straight Run Hazard Return rollers Possible Consequences Impact with rollers Crushed by falling rollers Protective Measures Throughway under conveyor more than 2 5 m Retaining device for return rollers figure 2 26 according to risk analysis results It is possible to reduce the risk with a preventative maintenance program which should be taken into account when doing the risk analysis FIGURE 2 26 RETURN ROLLER RETAINING DEVICE 37 Upper and Lower Strands in a Straight Run Hazard Bottom strand scrapers Possible Consequences Trapping and crushing Abrasions from the belt Protective Measures If hazard is less than 2 5 m from the floor or working platform In accordance with risk analysis results the scraper protection device may be combined with the drum protection device figure 2 27 and dimensions to be defined according to the opening that is necessary to adjust the scraper Add a guard to close the opening after adjustments FIGURE 2 27 SURROUNDING BARRIER GUARD FOR DRUM AND SCRAPER PARTIAL CAGE 38 2 6 4 Curved Zone Hazards In running nip between the belt and rollers in the curved zone Possible Consequences Drawing in Protective Measures If hazard is less than 2 5 m from the floor or working platform Surrounding in running nip or separation barrier guard figures 2 28 and 2 29 12. 2 6 8 Moving Sub Assemblies Hazard Pushers bumpers ejectors sorters Possible Consequences Crushing and shearing Protective Measures If hazard is less than 2 5 m from the floor or working platform Surrounding fixed or barrier guards figure 2 40 i poma S N E Floor FIGURE 2 40 TYPICAL BARRIERS FOR EJECTORS Note Leave a safe distance between the load and the guard so as not to create a trapping hazard Minimum distances are If the entire body can be drawn in 500 mm minimum If arms can be drawn in 120 mm minimum If legs can be drawn in 180 mm minimum 49 2 6 9 Moveable Conveyors Hazard Vertical and or horizontal movement Possible Consequences Crushing entanglement trapping Protective Measures If hazard is less than 2 5 m from the floor or working platform In accordance with risk analysis results barrier guard deterrent device or ground markings or signs to indicate the conveyor s operating area figure 2 41 It is also possible to use electronic safety devices surface detectors etc FIGURE 2 41 MOVEABLE CONVEYOR Note The limits of the operating area must be considered before applying protective measures 50 3 3 1 3 2 3 3 3 4 Safeguards against Other Hazards Hazards Generated by Poor Ergonomic Design Equipment must be designed so that operators and other users need not assume constraining work postures ov
3. Moreover start up must be confirmed by a distinct and deliberate manual action manual resetting The emergency stop command must have priority over all other commands and cannot be allowed to create dangerous situations such as load spillage The conveyor emergency stop device must also stop any downstream or upstream conveyors if their continued operation constitutes a safety hazard for workers section 193 of the Regulation Respecting Occupational Health and Safety An emergency stop device must not be used to bring the conveyor to an all stop state The emergency stop must not be used as a regular stop Remember that the installation of an emergency stop device does not replace appropriate protective devices As well emergency stop devices must not replace equipment lockout procedures during maintenance requiring access to danger zones For more information on the operation of emergency stop devices consult ISO Standard 13850 and NF EN 60947 5 5 53 4 4 Emergency Stop Pull Cords According to section 373 5 of the Regulation Respecting Occupational Health and Safety in Mines all conveyors must be equipped where the workers may access a conveyor while it is in operation with an emergency shut down device along its full length between the head pulley and the return pulley tail pulley Therefore for all mines the emergency shut down device must take the form of a cable spanning the full length of the conveyor In ot
4. 3 roller Min 620 mm ee 1 3 roller Min 1000 mm H Max 5 mm FIGURE 2 28 SURROUNDING aie FIXED GUARDS FOR Max 5 mm CURVED ZONE FIGURE 2 29 CURVED ZONE IN RUNNING NIP GUARD SEE TABLE 2 3 FOR C DIMENSION Note Belt edge tension is greater in the curved zones 39 2 6 5 Transition Zone Hazard In running nips between the upper strand and the load carrying rollers in the transition zone Possible Consequences Drawing in Protective Measures If hazard is less than 2 5 m from the floor or working platform Surrounding or in running nip figure 2 30 First transition roller FIGURE 2 30 PROTECTORS FOR HEAD DRUM AND TRANSITION ZONE TO DETERMINE LATERAL SCREEN HEIGHT SEE TABLE 2 2 40 2 6 6 Drums Hazards In running nips between belt and drums 1 of 2 Possible Consequences Drawing in Protective Measures If hazard is less than 2 5 m from the floor or working platform Surrounding in running nip or barrier guards figures 2 30 to 2 33 Max 5 mm FIGURE 2 31 IN RUNNING NIP GUARD FOR DRUM SEE TABLE 2 3 FOR C DIMENSIONS The distance between the scraper the drum and the belt must remain constant regardless of the bearing movement for adjustment etc FIGURE 2 32 SCRAPER SERVING AS AN IN RUNNING NIP GUARD 41 Drums Hazard In running nips between belt and drums 2 of 2 Ski
5. N Max 5 mm Min 120 mm FIGURE 2 36 POP UP ROLLER AT CONVEYOR BELT JUNCTION 44 2 6 7 Moving Loads Hazard Skirtboards Individual moving loads Possible Consequences Trapped between belt and skirtboard or between the load and the skirtboard Protective Measures If hazard is less than 2 5 m from the floor or working platform Workstation Limit the gap between the skirtboard and belt to a maximum of 5 mm Remove the skirtboard Design a surrounding fixed guard if need determined in risk analysis Other Areas Risk analysis Note When doing the risk analysis take into account the possibility of falling loads with the removal of the skirtboard 45 Moving Loads Hazard Individual loads and fixed obstacles not part of the conveyor e g post wall tunnel entrance enclave associated fixed equipment detectors etc large bulk sized loads e g boulders Possible Consequences Crushed between loads and fixed objects Shearing Impact with loads or other objects Protective Measures If hazard is less than 2 5 m from the floor or working platform Fixed guard or deterrent device figure 2 37 in accordance with risk analysis results in respecting the safe distances between loads and obstacles following are minimum distances for different situations If the entire body can be drawn in 500 mm minimum If arms can be drawn in 120 mm minimum If legs can be dra
6. ated by a positive action and be forced to break contact type device symbol illustrated in figure 2 42 FIGURE 2 42 STANDARD SYMBOL DESIGNATING FORCED TO BREAK CONTACT DEVICES Emergency stop devices must be installed at a height between 0 6 m and 1 7 m from the floor and must include the following gt One or more push button switches installed in such a manner that at least one is accessible within a 10 m distance from any equipment access point gt One or more emergency stop pull cords along the full conveyor length compulsory measure for mines where workers may have access to conveyors in operation section 373 5 of the Regulation Respecting Occupational Health and Safety in Mines gt A conveyor power disconnect device if the distance to the disconnect device is less than10 m from any conveyor access point An emergency stop device must allow equipment to shut down in the best possible manner that is by slowing down moving parts at an optimal rate by gt An immediate interruption of power to the motors gt A controlled stop motors remain energized to bring the equipment to a progressive stop and power is interrupted once the equipment has come to a halt The resetting of the emergency stop device must not by itself cause the start up of the machine unless the conveyor is a slow moving type and workers can access it safely section 270 of the Regulation Respecting Occupational Health and Safety
7. ation controls gt Control cables should be long enough to allow visual contact with the danger zone all the while making access to the danger zone impossible 5 4 Summary of Maintenance Safeguards Table 2 4 lists the safeguards required when carrying out most maintenance activities on conveyor belts or in proximity to conveyor belts They should be addressed in maintenance procedures The inching forward of an operation control should allow limited advance in separate steps no further advancement of machinery should be allowed until the operator releases the control device and then actuates the controls anew 56 Table 2 4 Safeguards for Maintenance Activities Activity Safeguards Repairs Changing mechanical electrical hydraulic or pneumatic parts on conveyors or related accessories Lockout conveyor or related accessory Belt replacement and splicing Lockout and application of a written safety procedure See S curit des convoyeurs a courroie guide du concepteur A Designer s Guide to Conveyor Belt Safety section 4 1 1 for required tools and facilities Welding and cutting Lockout if conveyor is located under the welding area Lockout if the closed unprotected danger zone is less than 2 500 mm from the work area Adjustment and fit Greasing and oiling lubrication around conveyor disposal of material recovered on the belt Authorized at all times provided adjustment p
8. danger zone the following safety precautions shall be taken 1 turn the machine s power supply switch to the off position 2 bring the machine to a complete stop 3 each person exposed to danger locks off all the machine s sources of energy in order to avoid any accidental start up of the machine for the duration of the work Lockout Procedures The goal of lockout procedures is to allow workers to carry out their tasks maintenance repairs cleaning etc on a conveyor and its accessories bumpers ejectors etc without risk Lockout procedures involve the following basics gt Bringing the machine to a complete stop gt Disconnecting all the machine s sources of power electric pneumatic hydraulic mechanical and thermal gt Dissipating all accumulated energy purging reservoirs removing counterweights unloading springs etc and checking for absence of energy gt Padlocking of energy disconnect devices by each worker accessing the work area gt Double checking to ensure that the equipment is in fact disconnected e g running a Start up test Consult document DD 754 2 ANSI Standard Z244 1 or the CSA Standard Z460 55 5 3 Safeguards for Maintenance within Operating Danger Zones Section 186 of the Regulation Respecting Occupational Health and Safety stipulates When a worker must access a machine s danger zone for adjustment unjamming maintenance apprenticeship or repair purposes i
9. erexert themselves or carry out repetitive movements Control devices must be grouped near workstations to allow operators and other users easy access They must be located outside danger zones so that activating them does not create hazards and workers do not have to enter the danger zones to access them To prevent unexpected start ups they must be positioned and protected Every workstation or intervention area must be provided with adequate lighting for the nature of the work being done or the nature of the work environment section 125 of the Regulation Respecting Occupational Health and Safety Heat Related Hazards Where conveyed products or any part of the equipment may cause burns take the following precautions gt Prevent contact with conveyed loads and hot or cold surfaces by the use of screens fixed surrounding or barrier guards gt Reduce the temperature of hot surfaces Electrical Hazards Conveyor electrical equipment must conform to the Qu bec Electrical Code Such equipment includes materials accessories devices appliances fasteners and other equipment used in the electrical power supply of a conveyor or in connection with a conveyor these include power disconnect devices In mines electrical equipment must also conform to the CAN CSA Standard M421 93 particularly those sections dealing with conveyors Fire and Explosion Hazards The use of conveyors can in itself be a fire and explosion hazard T
10. her workplaces an emergency stop cable may not be necessary where another shut down device has been installed in accordance with section 270 of the Regulation Respecting Occupational Health and Safety A sheathed metal strand cable shut down device must function as an emergency stop switch whatever direction the cable is pulled in or when it is broken A spring failure must also create an emergency stop A horizontal force of less than 125 N must be all that is needed to activate an emergency stop cable when applied midway between two support rings and perpendicularly to the cable The lateral movement of the cable between the position while at rest and the activation point must not exceed 300 mm The cable must be able to resist a tension force 10 times greater than the tension required to activate the emergency shut down switch when applied perpendicularly to the cable The cable must move freely within its supports particularly at bends Cables must not be twisted nor suffer the risk of being twisted during use If the belt width is equal to or less than 800 mm a single central cable may be used above the belt Maximum cable length and other characteristics must conform to the supplier s recommendations for support rings and pulley protection freeze up prevention variations in length due to temperature changes etc Sensitive cable devices may be used where activation of the switch is done by pressure compression torsi
11. hese hazards can be caused by the use of the conveyor itself or by the load the conveyor is carrying for example combustible particles These hazards may be amplified by tunnels or the stack effect Preventative measures to implement are described in division VIII of the Regulation Respecting Occupational Health and Safety and in section 374 of the Regulation Respecting Occupational Health and Safety in Mines In underground mines fire and explosion hazards related to belts can have particularly serious consequences Belts must conform to CAN CSA Standard M422 M87 51 4 1 4 2 4 3 Safeguards against Control System Failures or Malfunctions Start Up The start up of equipment must require a voluntary action Equipment start up must be prevented in the following situations gt The closing of a guard gt The actuation of an operation mode selector gt The resetting of an emergency stop device gt The resetting of a thermal protection device In conveyors designed to supply loads to other conveyors start up of the supply conveyor must be linked with the receiving conveyors using appropriate interlocking devices These devices must control and ensure proper sequential start up and prevent conveyor loading when not in use or when fully loaded For automatic or remote control start up conveyors as well as conveyors for which the operator or the user cannot see the entire conveyor a visual or audible warning device shall a
12. ncluding for detecting abnormal operations and to do so he must move or remove a protector or neutralize a protective device the machine shall only be restarted by means of a manual control or in compliance with a safety procedure specifically provided for allowing such access This manual control or this procedure shall have the following characteristics 1 it causes any other control mode or any other procedure as the case may be to become inoperative 2 it only allows the operating of the dangerous parts of the machine by a control device requiring continuous action or a two hand control device 3 it only allows the operation of these dangerous parts under enhanced security conditions for instance at low speed under reduced tension step by step or by separate steps For these measures to produce the desired results and given the serious hazards associated with conveyors they should incorporate the following recommendations gt Operation control devices including two hand controls should require hold to run input gt The operation control device used by the worker should have priority over all other control devices on the machine gt When maintenance is carried out by more than one worker while some hazards may be reduced those related to machine operation controls may increase establish a clear communication procedure to ensure clear communication between workers gt Prohibit the use of remote wireless oper
13. nnounce the starting of the conveyor sections 191 of the Regulation Respecting Occupational Health and Safety and 373 6 of the Regulation Respecting Occupational Health and Safety in Mines To prevent unexpected start ups replace two stable position toggle switches start stop with self powered contacts maintained by power or single stable position stable at the unenergized condition control devices These switches will bring the controls to an off circuit mode open contacts should there be a power outage or conveyor failure Regular Stop There must be a device or a method accessible to the operator and other users whereby equipment operations can be interrupted safely while guaranteeing that the equipment cannot be unexpectedly restarted An all stop switch is not designed to put an end to a recurring dangerous situation this is the role of an emergency stop switch A stop command must have priority over a start command Emergency Stop According to section 270 of the Regulation Respecting Occupational Health and Safety the emergency stop device of a conveyor to which workers have access comprises several control devices located at loading and unloading piers as well as at other points along the conveyor s itinerary In addition these devices have the following features 1 they are easily visible 2 one single action activates them 3 they are clearly identified 52 An emergency stop device should also be activ
14. ntact with a machine part for example to measure vibrations the point where the measurements are taken must be protected by a guard If a conveyor must remain operational while a guard is removed apply measures in section 5 3 Lockout for all other cases for example mechanical free play measurements Unclogging unjamming Lockout procedures apply Apply measures in section 5 3 should the conveyor need to be operational Maintenance activities not Lockout procedures apply at all times covered above Unclogging may create new specific hazards which must be analyzed before starting work hazard of falling in the hopper etc 58 6 6 1 6 2 Operator and Maintenance Crew Training All operators and maintenance workers who work on or in proximity to conveyors must be informed of the hazards they may encounter and receive training in established preventative measures and work procedures All safety related procedures and instructions must be documented Operator Training Only trained and authorized persons must be allowed to start up operate and interrupt the normal operation of a conveyor Among other things instruct operators in the following gt Conveyor start up gt Normal shut down and emergency stop devices gt Required checks before starting up a conveyor after an emergency shut down or accidental stoppage gt Proper loading procedures to avoid conveyor overload Maintenance C
15. oints for example scraper drum and take up system adjustment are outside the danger zone Lockout if adjustment points are inside the danger zone Application of stipulations in section 5 3 drum and scraper restrictions Authorized at all times where grease points are outside the danger zone Lockout if grease points are inside the danger zone Housekeeping under and Authorized at all times as long as the danger zone remains protected by a guard Particular attention should be paid to the space under an inclined belt located less than 2 5 m from the floor belt risk analysis Reminder A 300 mm high opening measured from the floor will help in housekeeping Lockout if the danger zone is not protected with a guard Apply measures in section 5 3 should the conveyor need to be operational Note Should the removal of material accumulation from an operating conveyor become frequent consider installing an operator work station Conveyor parts cleaning or maintenance drums rollers chassis etc Lockout procedures apply Operation authorized if housekeeping can be done gt With an automated jet air or water or gt According to section 5 3 above See also paragraph 3 4 Fire and Explosion Hazards 57 Inspection Visual and auditory inspection Permissible at all times as long as the worker remains outside the danger zone If the conveyor remains operational while the worker enters to make co
16. on or tension applied to the cable This method is best suited to complex cable runs and to dusty or heavy vibration environments 54 5 5 1 5 2 Safeguards against Maintenance Hazards S curit des convoyeurs courroie guide du concepteur A Designer s Guide to Conveyor Belt Safety provides additional information on this subject It discusses the incidence of the design factor on conveyor safety explains conveyor failure and diagnostics and suggests solutions for use during the problem solving process A fault tree helps establish the relationship between failures and accidents General Principles Equipment must be designed in such a way that maintenance adjustments greasing cleaning unjamming unclogging etc can be accomplished away from danger zones Therefore all adjustment and grease points must be accessible without having to remove guards or other protective devices When it is necessary to open or remove guards or even to neutralize protective devices in order to carry out a maintenance procedure safeguards must be implemented to ensure worker safety in the areas transformed into danger zones These measures must conform to sections 185 and 186 of the Regulations Respecting Occupational Health and Safety According to section 185 of the Regulation Respecting Occupational Health and Safety Subject to the provisions of section 186 before undertaking any maintenance repair or unjamming work in a machine s
17. rew Training Assign only knowledgeable and trained workers possessing the necessary technical expertise to maintain conveyors Assigned workers must be informed of the conditions under which the various maintenance tasks are to be completed Among other training they must be trained in lockout procedures When the removal of a guard or deterrent device is scheduled the assigned maintenance crew must receive detailed instructions related to their tasks including procedures for installing or repositioning guards or deterrent devices Supervisors and workers must check that guards and deterrent devices are back in place when maintenance tasks are completed 59
18. rt Min 620 mm in the Hopper board direction of belt k movement Max 300 mm a Max 550 mm FIGURE 2 33 SURROUNDING FIXED GUARD FOR TAIL DRUM Note If its not possible to comply with the 550 mm minimum distance between the in running nip and the bottom edge of the surrounding fixed guard the opening for housekeeping should be in accordance with table 2 1 42 Drums Hazard Take up system Possible Consequences Crushed by falling weights Drawn in at pinch points Protective Measures If hazard is less than 2 5 m from the floor or working platform Surrounding or barrier guards figures 2 33 and 2 34 If the weight is always more than 2 5 m from the floor or working platform Deterrent device guardrail to prevent access under the weight FIGURE 2 34 BARRIER GUARD FOR GRAVITY TYPE TENSIONER Note For gravity type tensioning devices the height of the barrier preventing access under the counterweight must be 2 500 mm Tensioner drums head or tail must also be protected 43 Drums Hazard Junction between two conveyors Possible Consequences Drawing in and trapping if the gap is greater than 5 mm Protective Measures If hazard is less than 2 5 m from the floor or working platform Fixed guard plate or free wheeling pop up roller figures 2 35 and 2 36 Max 5mm ae Ps 5 FIGURE 2 35 FIXED GUARD AT CONVEYOR BELT JUNCTIO
19. wn in 180 mm minimum FIGURE 2 37 TYPICAL PROTECTIVE MEASURES AGAINST HAZARDS ASSOCIATED WITH INDIVIDUAL LOADS AND FIXED OBSTACLES Note The objective is to keep the body arms and legs away from the crushing area The type of guard and its dimensions will depend upon body part at risk of being trapped and the weight of the load as determined in the risk analysis The guard must not in itself create a drawing in or trapping area 46 Moving Loads Hazard Load and load carrying rollers exceeding belt width Possible Consequences Trapping Crushing Protective Measures If hazard is less than 2 5 m from the floor or working platform Workstation Fixed barrier guard separation type or plates between rollers figure 2 38 Other Areas Fixed barrier guard Separation type or plates between rollers or deterrent device FIGURE 2 38 TYPICAL GUARD FOR INDIVIDUAL LOADS AND ROLLERS EXCEEDING BELT WIDTH 47 Moving Loads Hazard Loads falling from the belt Possible Consequences Impact with moving loads Crushed by falling loads Protective Measures If hazard is less than 2 5 m from the floor or working platform Protection plate mesh netting or guiding rail to maintain individual loads on the conveyor and prevent them from falling off in accordance with risk analysis results figure 2 39 FIGURE 2 39 TYPICAL PROTECTIVE DEVICES FOR THROUGHWAYS 48
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