4. Guards and other safety devices

Where there is danger from machinery operations, it is not desirable, nor wise, to rely solely upon safe working practices, essential though these are. Guards and other safety devices are useful as ultimate barriers to prevent injury when other precautions fail. Operation of a machine can only be efficient if there is no inherent danger.

An effective way of preventing injuries caused by machinery is to prevent the worker from coming into direct contact with the dangerous machine components, such as moving parts or high voltage wires. These dangerous parts should be guarded or protected in such a way as to prevent dangerous access at all times.

There are different kinds of guards. Fixed guards are set up around various dangerous parts such as rotating shafts, belts or drums, nips at ingathering rotating parts, projections, other moving parts of machinery, fast running or hot surfaces, etc. If frequent access to the area protected by a guard for changing parts or cleaning is necessary, interlocked guards can be applied. An interlocked guard prevents direct contact with danger as it must be back in position before the machine can be restarted. Automatic guards are also useful. One type of automatic guard pushes or pulls any part of a person away from the danger zone when necessary, for example, when working with cutting machines or presses. Another type of automatic guard uses a light beam which scans the danger area and falls on a photo-electric cell which is connected to a stop switch. When any part of a person comes within the area, the dangerous machine motion is stopped by a switch connected to the cell.

Automatic guards also include an automatically operated sliding screen which provides a temporary barrier between an operator loading a workpiece and the danger area. The screen rises to permit the working hands to enter and then prevents access to the danger area when the dangerous part of the machine is in operation.

Trip guards commonly include a trip bar or screen set to operate at a predetermined pressure which, when exceeded, causes the machines to stop with the assistance of braking devices when necessary. Two-handed controls require an operator to apply both hands to the controls in order to activate them. Such controls, however, should not be used as the sole means of protection when guarding is possible.

Other devices to improve safety include enclosure of dangerous machines or isolating them from workers. Finally, fail-safe arrangements are necessary, since equipment failures will be almost bound to occur. These failures produce a high percentage of accidents. Fail-safe arrangements are used to ensure that the occurrence of a failure will leave the system unaffected or convert it into a state in which no injury or damage can result. As example of fail-safe devices is the circuit-breaker which operates when an electrical system is overloaded. The circuit-breaker stops the system and prevents an electrical short-circuit.

It may be noted that mechanical guards and other safety devices can be extremely complex and expensive. However, simple and inexpensive devices can also be used to improve safety or sometimes productivity as seen in the following examples.

As a note of caution, it should be emphasised that in all cases of doubt, expert opinion should be sought. A faulty safety device is often worse than no device at all. It might merely lead to a false sense of security and thereby increase the risk of accidents.

Case 59: Low-cost machine guards

In Sri Lanka, there were 25 workers in a rice milling plant. Several incidences of crushed limbs occurred, including fatal and severe accidents. The owner was very concerned but unable to afford the standard wiremesh guards.

The Government sent a factory inspector to look into the situation. It was recommended that all the moving parts of the machinery - the electric motor, transmission belt and pulley, and the fan - should be fenced with narrow wooden strips firmly fixed into the floor. It is a basic and fundamental need to protect all moving parts of machines. Care was taken to ensure that the spaces between each wooden strip were narrow enough to prevent the limbs of workers from coming into contact with the moving parts of the machine.

The wooden guards were found to be effective in preventing injuries. The costs of the guards were not given but estimated to be low. The costs saved included the approximate sum of US$ 100 per year for compensation and accident leave before the improvement was made. The indirect benefit from better morale could not be shown in exact figures but it was found that profit increased by 20 per cent.

In this case, the small-scale enterprise Could not afford metal mesh and was satisfied with a much cheaper material, or wood. It must be pointed out that metal mesh is still more dependable and reliable than wood when used for machine guarding. Mesh is much finer and its effective lifetime is longer. More frequent replacements are therefore necessary for wood than wire mesh. It must be stressed that prompt replacement or repair of guards is always necessary to prevent accidents occurring as a consequence of inadequate or faulty guards.

Case 60: A guard for falling objects

In a granite quarry in Thailand, five workers manned the grinding section. The stones were taken by a trolley to an overhead platform where a workman dumped them onto a moving screen which allowed only granite pieces below a certain diameter to pass through. The workers at the second, lower level platform were frequently injured by falling stones which had missed the screen and fallen onto the passage and work-way.

The supervisor arranged for the construction of a metal apron attached to the screen to catch the falling stones. This was constructed by the workshop of the enterprise itself. As a result, there were no more accidents caused by falling stones.

The improvement cost about US$ 215 for material and four man-days, or US$ 24, for labour. The losses before the improvement amounted to about two man-days, or about US$ 10, per month due to injury leave and US$ 3 per month for first aid.

This case is instructive for several reasons. The injuries before the improvement was made were fortunately not severe. However, the situation was rightly assessed to be very dangerous, as serious injuries or severe fatalities could occur if no improvements were made. The solution was thought out and implemented by the enterprise itself. Costs were therefore relatively minor but the effect was gratifying. It should be pointed out that the solution employed was far more effective than the provision of safety helmets alone, although these should also be used as a supplementary measure.

Case 61: Prevention of foot injuries by trolleys

In a manufacturing plant in Singapore, workers suffered injuries when trolleys used for transporting heavy loads rolled over their toes.

After several unsuccessful attempts at solutions, the safety officer of the enterprise devised a guard for the trolley wheels. It was made of metal, rectangular in shape and fixed to the wheel in such a way that the wheels could still move freely. The outside of the guard was padded with rubber. Now the wheels of the trolley would not roll over the workers' toes, and would be pushed away by the padded guard.

Since the installation of the guards, no foot injury has occurred in the factory. The wheel guards were made and installed by the workers themselves and cost only US$ 1.50 each. The exact costs from the injuries, including medical expenses and loss of productivity, were not given but said to have been considerable.

Foot injuries from trolleys are quite common. In many developing countries, workers often go around barefoot or in sandals, which make them even more vulnerable to such foot injuries. In this case, apart from the installation of trolley guards, workers should also be protected by the use of proper footwear. For handling heavy loads, safety shoes or boots are essential to prevent foot injuries.

Figure 94: Guard preventing contact between the wheel and the workers' foot.

Case 62: A shield for face protection

In a radio manufacturing plant in Indonesia, several workers were engaged in cutting off component legs under particle circuit boards. The cutting process was done in a dark box, but the fragments cut off the boards could easily fly out and injure the workers' eyes.

A box furnished with a glass plate and a fluorescent lamp was made using plywood boards. The box was 48 cm high. After some trials, the glass plate was installed parallel to the workers' eyes. All the fragments from the cutting process now fell back into the box. A box was made for each worker doing cutting work. The workers were pleased because their eyes were protected and they could see the process more clearly with the help of the lamp. The provision of the boxes also helped keep the workplace clean.

The materials cost US$ 6.50 per box including plywood boards, a fluorescent lamp and a glass plate.

Figure 95: Cutting off component legs under a particle circuit board.

In the grinding and polishing section of a large jewellery factory in Thailand, bits of metal tended to fly off the grinding wheels, thereby causing a hazard to the face and eyes of the workers. The factory employed 120 workers, 30 of whom were engaged in polishing, buffing and grinding.

A sheet of thick glass was inserted in front of each grinding wheel. It was fixed to the wheel with a hinge so as to facilitate cleaning and adjustment to the grinding wheel. The result was totally effective, as no eye or facial injuries occurred thereafter. The cost of the glass was minimal and the cost of labour nil, as the installation was done by the artisans of the factory.

Figure 96: A protective box with a glass plate and a lamp for cutting work.

Eye or facial injuries from flying objects are frequent and can be serious. Many cases of blindness have occurred as a result. Yet prevention of such injuries is often simple and inexpensive, as shown by these examples. The glass should be cleaned regularly or replaced if necessary. A dirty or excessively scratched glass can hamper visibility and workers may be tempted to remove the guard, thereby endangering themselves. In addition, it should be emphasised that safety screens of ordinary glass are only effective against small flying objects. They should not be used against heavy flying objects or small objects ejected at high velocity. Goggles or other forms of eye protection may also be required in addition to glass screens.

Case 63: A glass window guard against flying particles

Women workers in a polishing section of a wholesale jewellery house in Thailand were at times exposed to particles from small grinding machines flying into their face and eyes. About ten workers were engaged in the section. Goggles did not seem effective as the workers tended to take them away during polishing work. All the grinding machines were positioned as to revolve in the downward direction. It was necessary to set up a permanent face guard to prevent possible injuries.

Two wooden cabinets were built around a series of grinding machines so that the polishing work could be done by looking through a glass window. Each cabinet covered four workstations. Each window was made so that the worker could easily see the items to be polished and the movements of the hands inserted underneath the window were not disturbed. All the windows could be easily opened in the case of maintenance work in the grinding machines.

Figure 97: A wooden cabinet with windows to protect against flying particles from grinders.

The manufacture of the two cabinets was contracted with a small shop. The cost for covering the eight workstations in two lines was US$ 145. The work was done during a weekend break.

After the installations of the cabinets, no facial or eye injuries occurred. This allowed the company to save medical expenses which were estimated to be US$ 75 a year. Though not measurable in monetary terms, costs could also be saved by eliminating lost time due to these injuries or other difficulties such as delay in jewellery delivery or turnover of the workers.

Case 64: Wire mesh and metal sheet guards against metal chips

In an enamelware manufacturing factory in Burma, there was a need to safeguard beading machine operators and others around them. They were endangered by metal chips flying out of the machines. The safety committee looked into the matter. Each beading machine was run by a 1.5 horse power motor and worked on the general principles of a simple lathe. While a workpiece mounted on the head stock revolved, the edge would be cut and the rim rounded simultaneously. When the edges of the pressed metalware were cut off, some chips would fly a distance of up to about 5 metres away from the machine on the opposite side of the operator. On some occasions when the operator handled the slide, chips would even fly towards him.

Figure 98: The beading machine without guards.

There were six such machines, installed in two rows six metres apart. Between the two rows of machines at just about the middle, a wire mesh partition was built. Then a wire mesh shield was erected on the vertical plane just above the machine at a height of 90 cm, with a small opening just above the joint of operation. The top side was also covered by wire mesh. A piece of sheet metal, cut and shaped as half of a square metal container cut diagonally across, was fitted onto the machine just beyond the cutting point and very close to it. These guards proved suitable. The flying chips were caught by the wire mesh partitions.

Figure 99: An operator working on the machine with a mesh guard erected in front.

The square mesh partitions with wooden frames for each machine cost about US$ 48. The labour cost was not added as they were made by the factory staff. The small guard on each machine cost only US$ 10. The wire mesh partition near the wall in front of the machines cost US$ 70.

Figure 100: The operator working with a sheet metal guard on the machine.

Case 65: Prevention of arm laceration

In a small plastic moulding factory in Singapore, five cases of severe laceration on the forearms of workers were reported within a period of a few months. The workers were all engaged in trimming the plastic products with a small knife. Sometimes the knife would slip and wound the workers.

The safety officer in the factory investigated the problem. He contacted a company which made rattan products. He arranged for a supply of rattan meshing which was wrapped around the forearms of workers and kept firmly in place by rubber garters. Several trials were conducted to ascertain the optimum length and breadth of the meshing needed. The meshing was found to be effective in preventing arm lacerations.

Figure 101: Rattan mesh and knife used in trimming plastic products.

The rattan meshing for each worker cost US$ 7.50. Recurrent costs for replacement of worn-out meshing could not be calculated as the period of observation was still too short for this purpose. However, such recurrent costs were estimated to be quite small.

Savings in terms of prevention of injury and medical expenses far exceeded the costs incurred. Moreover, the productivity of the workers was enhanced because they could work faster now that the fear of sustaining lacerations was removed. This case is a good example of a working procedure being made more safe by a low-cost guard improvised by the factory itself and using material readily available locally.

Figure 102: Trimming operation in progress.

Figure 103: The rattan meshing now prevents lacerations to the forearm.

Case 66: Welding partitions

Workers of a metal fabrication factory in the Philippines were often disturbed by glare from several welders at work. There were about 60 workers with at least three welders operating simultaneously. The house-keeping conditions of the factory were poor and the welding took place at different parts of the fabrication area of about 800 square metres depending on the situation. The glare from welding caused distractions and inconvenience to non-welders working in the area.

To reduce the glare caused by welding, the owner decided to designate a particular section of the work area as a welding place and to provide partitions around it. He surveyed his factory for light and portable materials that could be used to shield the glare. Available scrap aluminium braces and leftover plywood were given to two workers to make into partitions. A total of six partitions were made.

The owner provided the welders with these partitions and instructed them to use these to contain glare from welding work. The welders readily preferred to work within the confines of these partitions. In fact, according to the owner, they competed for the use of partitions. The non-welders said that there was no more distraction caused by the direct glare from welding work.

The cost for making six partitions included about US$ 40 for scrap aluminium and plywood and about US $15 for four working days (two workers spending two days each for making the partitions). The approximate cost per partition was about US$ 9. Compared with the cost incurred, the advantage of the use of these partitions was remarkable. Though accurate comparison was not readily available, the owner was expecting enhanced productivity and fewers errors by workers formerly affected by the glare.

Case 67: Two-hand device for a foot-operated power press

In a small metalworking factory in Thailand, there were several hand injuries caused by a power press. The power press was being used by workers of a metal cutting unit. The maintenance staff of the factory studied the possibility of incorporating a safety device into the foot-operated power press. It was decided to introduce a two-hand control system in place of a foot lever. The system would require the worker to put both hands simultaneously on two buttons in order to activate the press. It would prevent any hand from coming into contact with the dangerous part in motion.

A design was drawn up by the maintenance department. A small pneumatic cylinder was put on top of the foot lever of the press, connected to a switch and a compressed air system, and the switch was linked to an electric power line which had a two-hand control switch installed on the front side of the power press. All the work was done by maintenance workers.

The cost of refitting the two-hand control system on the press was approximately US$ 55, not inclusive of labour costs.

All workers were trained on safe press operation. The incidence of hand injuries dropped significantly.

Figure 104: A pneumatic cylinder connected to a two-hand switch to control a power press.

Figure 105: Feeding materials into the power press.

Figure 106: Two-hand control to ensure that the hands are away from the danger zone.

Case 68: Protective handrails near steam vats

In a plywood factory in Burma, round logs were placed into steam vats and steamed for a period of three to five days. While placing logs into the vats and taking them out, the workers faced the risk of getting splashed by hot water at about 90°C and of slipping and falling into the vats. The workers also complained of the narrow foot space on the edges of the tanks.

After studying the work process at the steam vats, portable handrails were manufactured. At the same time, the wooden covers for the vats were replaced. Work at the vats was arranged so that when work was done at a particular vat, the vat adjacent to it would be covered. Instead of working on the edges of the vats, the workers would be stationed by the cover placed over the adjacent vat with a handrail fitted in front for protection. The overhead crane clearance at these workplaces was readjusted to ensure safe clearance for crane movement during work.

Construction of a wooden cover and handrails for a medium-size vat cost approximately US$ 240 including labour costs of US$ 32 for a carpenter. The cost for a cover and handrails for a large-size vat was US$ 470 including labour costs of about US$ 170. Second class teak, brackets and iron-ring fasteners were used.

Figure 107: Workers working at the vats without protective guards.

The work at the hot vats became safe. For a period of two years after these modifications, not a single case of splash burns or falling into the vats occurred.

Figure 108: Working at the vats with protective handrails.