PRINCIPLES OF PREVENTION: MATERIALS HANDLING AND INTERNAL TRAFFIC
Materials handling and internal traffic are contributing factors in a major portion of accidents in many industries. Depending on the type of industry, the share of work accidents attributed to materials handling varies from 20 to 50%. The control of materials-handling risks is the foremost safety problem in dock work, the construction industry, warehousing, sawmills, shipbuilding and other similar heavy industries. In many process-type industries, such as the chemical products industry, the pulp and paper industry and the steel and foundry industries, many accidents still tend to occur during the handling of final products either manually or by fork-lift trucks and cranes.
This high accident potential in materials-handling activities is due to at least three basic characteristics:
· High amounts of potential and kinetic energies, which have the propensity for causing injury and damage, are found in transport and handling.
· The number of people required at transport and handling workplaces is still relatively high, and they are often exposed to the risks associated with such sites.
· Whenever several dynamic operations have to be carried out simultaneously and require cooperation in varying environments, there is an especially urgent need of clear and timely communication and information. The consequently high liability of many types of human errors and omissions may create hazardous situations.
Every time people or machines move loads, an accident risk is present. The magnitude of risk is determined by the technological and organizational characteristics of the system, the environment and the accident prevention measures implemented. For safety purposes, it is useful to depict materials handling as a system in which the various elements are interrelated (figure 58.103). When changes are introduced in any element of the system-equipment, goods, procedures, environment, people, management and organization-the risk of injuries is likely to change as well.
Figure 58.103 A materials-handling system
The most common materials-handling and internal traffic types involved in accidents are associated with manual handling, transport and moving by hand (carts, bicycles, etc.), lorries, fork-lift trucks, cranes and hoists, conveyors and rail transport.
Several types of accidents are commonly found in materials transport and handling at workplaces. The following list outlines the most frequent types:
· physical strain in manual handling
· loads falling onto people
· people trapped between objects
· collisions between equipment
· people falling
· hits, blows and cuts to people from equipment or loads.
Elements of Materials-Handling Systems
For each element in a materials-handling system, several design options are available, and the risk of accidents is affected accordingly. Several safety criteria must be considered for each element. It is important that the systems approach is used throughout the lifetime of the system-during the design of the new system, during the normal operation of the system and in following up on past accidents and disturbances in order to introduce improvements into the system.
General Principles of Prevention
Certain practical principles of prevention are generally regarded as applicable to safety in materials handling. These principles can be applied to both manual and mechanical materials-handling systems in a general sense and whenever a factory, warehouse or construction site is under consideration. Many different principles must be applied to the same project to achieve optimum safety results. Usually, no single measure can totally prevent accidents. Conversely, not all of these general principles are needed, and some of them may not work in a specific situation. Safety professionals and materials-handling specialists should consider the most relevant items to guide their work in each specific case. The most important issue is to manage the principles optimally to create safe and practicable materials-handling systems, rather than to settle upon any single technical principle to the exclusion of others.
The following 22 principles can be used for safety purposes in the development and assessment of materials-handling systems in their planned, present or historical stage. All of the principles are applicable in both pro-active and aftermath safety activities. No strict priority order is implied in the list that follows, but a rough division can be made: the first principles are more valid in the initial design of new plant layouts and materials-handling processes, whereas the last principles listed are more directed to the operation of existing materials-handling systems.
Twenty-two Principles of Prevention of Materials-Handling Accidents
1. Eliminate all unnecessary transport and handling operations. Because many transport and handling processes are inherently dangerous, it is useful to consider whether some materials handling might be eliminated. Many modern manufacturing processes can be arranged in a continuous flow without any separate handling and transport phases. Many assembly and construction operations can be planned and designed to eliminate strenuous and complex movements of loads. Options for more effective and rational transport can also be found by analysing logistics and material flow in the manufacturing and transport processes.
2. Remove human beings from the transport and handling space. When workers are not physically located under or in the vicinity of loads to be moved, safety conditions are ipso facto improved because of reduced exposure to hazards. People are not allowed to work in the scrap-handling area of steelworks because pieces of scrap may drop from the magnetic grippers that are used to move the scrap, presenting a continuous hazard of falling loads. Materials handling in harsh environments can often be automated by using robots and automatic trucks, an arrangement that reduces the accident risks posed to workers by moving loads. Moreover, by forbidding people to go unnecessarily through loading and unloading yards, exposure to several types of materials-handling hazards is basically eliminated.
3. Segregate transport operations from each other as much as possible to minimize encounters.The more frequently vehicles encounter one another, other equipment and people, the greater is the probability of collisions. Segregation of transport operations is important when planning for safe in-plant transport. There are many segregations to be considered, such as pedestrians/vehicles; heavy traffic/light traffic; internal traffic/traffic to and from outside; transport between workplaces/materials handling within a workplace; transport/storage; transport/production line; receiving/shipping; hazardous materials transportation/normal transport.
When spatial segregation is not practicable, specific times can be allocated when transport and pedestrians respectively are allowed to enter a work area (e.g., in a warehouse open to the public). If separate pathways cannot be arranged for pedestrians, their routes can be designated by markings and signs. When entering a factory building, employees should be able to use separate pedestrian doors. If pedestrian traffic and fork-lift truck traffic are mixed in doorways, they also tend to be mixed beyond the doorways, thus presenting a hazard. During plant modifications, it is often necessary to limit transport and human motion through the areas which are under repair or construction. In overhead crane transport, collisions can be avoided by seeing to it that the tracks of the cranes do not overlap and by installing limit switches and mechanical barriers.
4. Provide enough space for materials-handling and transport operations. Too narrow a space for materials handling is often a cause of accidents. For example, workers’ hands can be caught between a load and a wall in manual handling, or a person may be pinned between a moving pillar of a transport crane and a stack of materials when the minimum safety distance of 0.5 m is not available. The space needed for transport and handling operations should be carefully considered in plant design and planning of modifications. It is advisable to reserve some “safety margin” of space in order to accommodate future changes in load dimensions and types of equipment. Often, the volume of the products being manufactured tends to grow as time goes on, but the space in which to handle them becomes smaller and smaller. Although the demand for cost-effective space utilization may be a reason for minimizing production space, it should be borne in mind that the manoeuvring space needed for counterbalanced fork-lift trucks to turn and to backtrack is larger than it seems to be at first sight.
5. Aim at continuous transport processes, avoiding points of discontinuity in materials handling. Continuous material flows reduce the potential for accidents. The basic arrangement of a plant layout is of crucial importance in carrying out this safety principle. Accidents concentrate in places where the material flow is interrupted because the moving and handling equipment is changed, or for production reasons. Human intervention is often required to unload and reload, to fasten, package, lift and drag, and so forth. Depending on the materials handled, conveyors generally give more continuous material flows than cranes or fork-lift trucks. It is good planning to arrange transport operations in such a way that motor vehicles can move in factory premises in a one-way circle, without any zigzag motion or backtracking. Because points of discontinuity tend to develop in boundary lines between departments or between working cells, production and transport should be planned to avoid such “no-man’s lands” with uncontrolled materials movement.
6. Use standard elements in materials-handling systems. For safety purposes it is generally better to use standard items of loads, equipment and tools in materials handling. The concept of unit load is well-known to most transport professionals. Materials packed in containers and on pallets are easier to attach and move when the other elements in the transport chain (e.g., storage racks, fork-lift trucks, motor vehicles and fastening devices of cranes) are designed for these unit loads. The use of standard types of fork-lift trucks with similar controls decreases the probability of driver error, as accidents have occurred when a driver has changed from one sort of equipment to another with different controls.
7. Know the materials to be handled. Knowledge of the characteristics of the materials to be transported is a precondition for safe transfer. In order to select appropriate lifting or load restraints, one must take into account the weight, centre of gravity and dimensions of goods that are to be fastened for lifting and transport. When hazardous materials are handled, it is necessary that information be available as to their reactivity, flammability and health hazards. Special hazards are presented in the case of items which are fragile, sharp, dusty, slippery, loose, or when handling explosive materials and living animals, for example. The packages often provide important information for workers as to proper handling methods, but sometimes labels are removed or protective packaging conceals important information. For example, it may not be possible to view the distribution of the contents within a package, with the result that one cannot properly assess the load’s centre of gravity.
8. Keep the loading below the safe working-load capacity. Overloading is a common cause of damage in materials-handling systems. Loss of balance and material breakage are typical results of overloading handling equipment. The safe working load of slings and other lifting tackle should be clearly marked, and proper configurations of slings must be selected. Overloading can take place when the weight or the centre of gravity of the load is misjudged, leading to improper fastening and manoeuvring of loads. When slings are used to handle loads, the equipment operator should be aware that an inclined pathway may exert forces sufficient to cause the load to drop off or over-balance the equipment. The loading capacity of fork-lift trucks should be marked on the equipment; this varies according to the lifting height and the size of the load. Overloading due to fatigue failure may occur under repeated loadings well below the ultimate breaking load if the component is not correctly designed against this type of failure.
9. Set the speed limits low enough to maintain safe movement. Speed limits for vehicles moving in workplaces vary from 10 km/h to 40 km/h (about 5 to 25 mph). Lower speeds are required in inside corridors, in doorways, at crossings and in narrow aisles. A competent driver can adapt a vehicle’s speed according to the demands of each situation, but signs notifying drivers of speed limitations are advisable at critical places. The maximum speed of a remote-controlled mobile crane, for example, must be determined first by fixing a vehicle speed comparable to a reasonable walking speed for a human, and then allowing for the time needed for simultaneous observations and control of loads so as not to exceed the response time of the human operator.
10. Avoid overhead lifting in areas where people are working underneath. Overhead lifting of materials always poses a risk of falling loads. Although people are ordinarily not allowed to work under hanging loads, the routine transportation of loads over people in production can expose them to danger. Fork-lift transport to high storage racks and lifting between floors are further examples of overhead lifting tasks. Overhead conveyors transporting stones, coke or casts may also constitute a risk of falling loads for those walking underneath if protective covers are not installed. In considering a new overhead transport system, the potential greater risks should be compared with the lesser risks associated with a floor-level transport system.
11. Avoid materials-handling methods that require climbing and working at high levels. When people have to climb up-for example, to unfasten sling hooks, to adjust a vehicle’s canopy or to make markings on loads-they risk falling. This hazard can often be averted by better planning, by changing the sequence of work, by using various lifting accessories and remote-controlled tools, or by mechanization and automation.
12. Attach guards at danger points. Guards should be installed on danger points in materials-handling equipment such as the chains of fork-lift trucks, the rope drives of cranes and the trapping points of conveyors. Out-of-reach protection is often not enough, because the hazard point may be reached by using ladders and other means. Guards are also used to protect against technical failures that could lead to injuries (e.g., of wire rope retainers on crane sheaves, safety latches in lifting hooks and the protection pads of textile slings that shield against sharp edges). Guardrails and toeboards installed against the edges of loading platforms and overhead storage racks, and around floor openings, can protect both people and things from falling. This sort of protection is often needed when fork-lift trucks and cranes lift materials from one floor to another. People can be protected from falling objects in materials-handling operations by safety nets and permanent guards such as wire mesh or metal plate covers on conveyors.
13. Transport and lift people only by the equipment designed for the purpose. Cranes, fork-lift trucks, excavators and conveyors are machines for moving materials, not human beings, from one place to another. Special lifting platforms are available to lift persons, for example, to change lamps on ceilings. If a crane or a fork-lift truck is equipped with a special cage which can be securely attached to the equipment and which meets proper safety requirements, persons can be lifted without an excessive risk of severe injury.
14. Keep equipment and loads stable. Accidents happen when equipment, goods or storage racks lose their stability, especially in the case of fork-lift trucks or mobile cranes. The selection of actively stable equipment is a first step to reduce hazards. Further, it is advisable to use equipment that emits a warning signal before the limit of collapse is reached. Good working practices and qualified operators are the next stops of prevention. Experienced and trained employees are able to estimate centres of gravity and recognize unstable conditions where materials are piled and stacked, and to make the necessary adjustments.
15. Provide good visibility. Visibility is always limited when handling materials with fork-lift trucks. When new equipment is purchased, it is important to assess how much the driver can see through the mast structures (and, for high-lifting trucks, the visibility through the overhead frame). In any case, the materials handled cause some loss of visibility, and this effect should be considered. Whenever possible, a clear line of sight should be provided-for example, by removing piles of goods or by arranging openings or empty sections at critical points in racks. Mirrors can be applied to the equipment and at suitable locations in factories and warehouses to make blind corners safer. However, mirrors are a secondary means of prevention compared to the actual elimination of blind corners in order to allow direct vision. In crane transport it is often necessary to assign a special signal person to check that the area where the load will be lowered is unoccupied by people. A good safety practice is to paint or otherwise mark danger points and obstructions in the working environment-for example, pillars, edges of doors and of loading docks, protruding machine elements and moving parts of equipment. Appropriate illumination can often improve visibility considerably-for example, on stairs, in corridors and at exit doors.
16. Eliminate manual lifting and carrying of loads by mechanical and automated handling. About 15% of all work-related injuries involve the manual lifting and carrying of loads. Most of the injuries are due to over-exertion; the rest are slips and falls and hand injuries inflicted by sharp edges. Cumulative trauma disorders and back disorders are typical health problems due to manual-handling work. Although mechanization and automation have eliminated manual-handling tasks to a large extent in industry, there still exist a number of workplaces where people are physically overloaded by lifting and carrying heavy loads. Consideration should be given to providing appropriate handling equipment-for example, hoists, lifting platforms, elevators, fork-lift trucks, cranes, conveyors, palletizers, robots and mechanical manipulators.
17. Provide and maintain effective communication. A common factor in serious accidents is a failure in communication. A crane driver must communicate with a slinger, who fastens the load, and if the hand signs between the driver and the loader are incorrect or radio phones have a low audibility, critical errors may result. Communication links are important between materials-handling operators, production people, loaders, dock workers, equipment drivers and maintenance people. For instance, a fork-lift truck driver has to pass along information about any safety problems encountered-for example, aisles with blind corners due to stacks of material-when turning over the truck to the next driver during shift change. Drivers of motor vehicles and mobile cranes working as contractors in a workplace are often unfamiliar with the particular risks they may encounter, and should therefore receive special guidance or training. This may include providing a map of the factory premises at the access gate together with the essential safe work and driving instructions. Traffic signs for workplace traffic are not as highly developed as the those for public roads. However, many of the risks encountered in road traffic are common within factory premises, too. It is therefore important to provide appropriate traffic signs for internal traffic in order to facilitate the communication of hazard warnings and to alert drivers to whatever precautions may be required.
18. Arrange the human interfaces and the manual handling according to ergonomic principles. Materials-handling work should be accommodated to the capacity and skills of people by applying ergonomics so as to obviate errors and improper straining. The controls and displays of cranes and fork-lift trucks should be compatible with the natural expectations and habits of people. In manual handling it is important to make sure that there is enough space for the human motions necessary to carry out the tasks. Furthermore, excessively strenuous working postures should be avoided-for example, manually lifting loads over one’s head, and not exceeding the maximum permissible weights for manual lifting. Individual variations in age, strength, health status, experience and anthropometric considerations may require modification of the workspace and tasks accordingly. Order picking in storage facilities is an example of a task in which ergonomics is of utmost importance for safety and productivity.
19. Provide adequate training and advice. Materials-handling tasks are often regarded as too low-status to warrant any special training for the workforce. The number of specialized crane operators and fork-lift drivers is decreasing at workplaces; and there is a growing tendency to make crane and fork-lift truck driving a job that almost anybody in a workplace should be prepared to do. Although hazards can be reduced by technical and ergonomic measures, it is the skill of the operator that is ultimately decisive in averting hazardous situations in dynamic work settings. Accident surveys have indicated that many of the victims in materials-handling accidents are people not involved in materials-handling tasks themselves. Therefore, training should also be provided to some extent for bystanders in the materials-handling areas.
20. Supply the people working in transport and handling with appropriate personal outfits. Several types of injuries can be prevented by using appropriate personal protective equipment. Safety shoes which do not cause slips and falls, heavy gloves, safety glasses or goggles, and hard hats are typical personal protectors worn for materials-handling tasks. When special hazards demand it, fall protection, respirators and special safety garments are used. Appropriate working gear for materials handling should provide good visibility and should not include parts that may easily be caught on equipment or gripped by moving parts.
21. Carry out proper maintenance and inspection duties. When accidents happen because of failures in equipment, the reasons are often to be found in poor maintenance and inspection procedures. Instructions for maintenance and inspections are given in safety standards and in manufacturers’ manuals. Deviations from the given procedures can lead to dangerous situations. Material-handling equipment users are responsible for daily maintenance and inspection routines involving such tasks as checking batteries, rope and chain drives, lifting tackle, brakes and controls; cleaning windows; and adding oil when needed. More thorough, less frequent, inspections are carried out regularly, such as weekly, monthly, semi-annually or once a year, depending on the conditions of use. Housekeeping, including adequate cleaning of floors and workplaces, is also important for safe materials handling. Oily and wet floors cause people and trucks to slip. Broken pallets and storage racks should be discarded whenever observed. In operations involving the transporting of bulk materials by conveyors it is important to remove accumulations of dust and grain in order to prevent dust explosions and fires.
22. Plan for changes in the environmental conditions. The capacity to adapt to varying environmental conditions is limited among equipment and people alike. Fork-lift truck operators need several seconds to adapt themselves when driving from a gloomy hall through doorways to a sunlit yard outside, and when moving inside from outdoors. To make these operations safer, special lighting arrangements can be set up at doorways. In the outdoors, cranes are often subjected to high wind loads, which have to be taken into account during lifting operations. In extreme wind conditions, lifting with cranes must be interrupted entirely. Ice and snow may cause considerable extra work for workers who have to clean the surfaces of loads. Sometimes, this also means taking extra risks; for instance, when the work is done upon the load or even under the load during lifting. Planning should cover safe procedures for these tasks, too. An icy load may glide away from a pallet fork during a forklift transport. Corrosive atmospheres, heat, frost conditions and seawater can cause degradation of materials and subsequent failures if the materials are not designed to withstand such conditions.