2. Heat and noise

Most of the developing countries lie in the tropical or sub-tropical regions of the world. A hot and humid climate is therefore common in such countries and may lead to heat and ventilation problems. In addition, manufacturing equipment and processes are probably equally common as causes of heat problems. Examples of heat-producing equipment and processes include furnaces for smelting, heating and other activities, welding, boilers, glass-making and generators. Hard physical work increases heat production within the body and thus adds to the heat problem in hot workplaces. Often heat problems result from the combination of the weather, manufacturing processes and poor ventilation.

Excessive heat affects the comfort and productivity of workers. They may become restless, lose their powers of concentration or feel dizzy. Sometimes workers may develop body aches and muscle cramps. These cramps are due to excessive loss of water and salt from the body through perspiration. Occasionally, the heat may be so severe as to affect the brain. The workers may then suddenly lose consciousness. In such severe cases, death may occur.

Noise is also a widespread problem in enterprises. Machines for stamping, pressing, rivetting or punching metal parts are often very noisy. Weaving looms, bottling apparatus and generators can also produce a lot of noise. In construction, piling machines and many other pieces of equipment can create noise problems. There are also many other sources of high noise levels in small as well as large enterprises.

There is a simple way to determine whether the noise level is dangerous to hearing or not. When a person has to shout to enable another person with normal hearing to hear his words one or two metres away, this usually means the noise level is about 85 dB. There are more elaborate ways of measuring and analysing noise by sound level metres, and these are usually needed for precise monitoring.

There are many low-cost ways of reducing heat or noise problems. Isolation of the sources of heat or noise can be universally applied. Workplaces should be spacious and, especially to reduce heat effects, have adequate windows or doors to allow for good air flow. Walls and roofs should not be made of materials which reflect noise or which are good conductors of solar heat. In other situations, we could use enclosure or insulation of heated machines or pipes or noisy machines. If heat radiation is great, for example from furnaces, workers can be shielded from it by a barrier or screen.

The heat or noise may sometimes still be excessive in spite of available measures. In this case, consideration should be given to drastic technical solutions, such as purchasing cooler or quieter machines or air-conditioning, or, as a last resort, providing protective clothing or ear muffs or plugs.

The following examples illustrate how enterprises have coped with severe heat or noise problems by making simple improvements in the environment. They show that such improvements in the physical environment need not always be expensive.

Case 45: Wider windows and ventilators

In a laundry section of a hotel in Bali, Indonesia, about 15 workers were working in hot and humid conditions. The lack of air movement was obviously aggravating the effects of heat. It was therefore decided to have new openings and windows and to install a few ventilators.

US$ 150 was spent on constructing new windows and openings as shown in figures 75 and 76, Another US$ 60 were spent on ventilators. The air movement improved greatly and the laundry room became cooler. This had a positive impact on the productivity of the workers. The lighting conditions of the room also improved.

Figure 75: High windows and a ventilator in a hotel laundry section.

Figure 76: Ventilation openings in a hotel laundry section.

In a factory producing bangles made of glass in Bangladesh, there were 18 workers in the finishing section. A small heater was used to temper bangles. The workers complained of excessive heat and burns occasionally caused due to handling the iron handles of the heater. The frequent turnover of workers in this section seemed related to the work strain.

A small electric fan was installed on the workroom wall. A wooden handle was fitted to the iron handle of the heater. It was also arranged to increase ventilation in the room by keeping windows and doors open. The improvements were done at low cost. The electrical fan cost US$ 43, the wooden handle US$ 1, and arrangements for cross ventilation about US$ 4. Though no records were available about the production or rejection of products, the management noted a significant reduction in rejected products.

Installation of a ventilator in a varnishing section of a furniture factory with 10 workers in the Philippines also proved useful for the reduction of the heat load of the workers at low cost. Although there were wide windows, the whole building was surrounded by high and thick walls which prevented the air from entering. The manager, after discussing the matter with a supervisor and the workers, installed a ventilator at an appropriate place. This cost US$ 140. Its life span was considered to be ten years or more. With the improved ventilation, the room became cooler. A worker could now varnish ten chairs a day, while before he could hardly varnish eight. The frequency of repeating the finishing touches on the furniture also was reduced.

Case 46: Barriers for thermal radiation

Thermal radiation from furnaces, molten metal and slag produced adverse effects on the workers of a flash smelting shop in Calcutta, India. Many of the 225 workers employed in the shop were exposed to high thermal radiation. The hot metal splashes and sparks also caused injury and fire hazards. The factory asked for advice about low-cost solutions.

An adjustable thermal radiation barrier and hinged covers for channels carrying molten slag seemed practical solutions. As polished aluminium thermal barriers were costly and required regular cleaning, two oxidised iron sheets of one metre by one metre each in size were used to form a thermal barrier, with a gap of 25 cm between them. The two sheets were fixed with iron rods at the four corners and at the middle. The thermal barrier was placed between the sources of high thermal radiation and the workers. The barrier was put on two low-cost stands with different points of suspension. The lower part of the barrier stand was kept open for the circulation of air between the sheets.

The covers over the channels for molten slag were fixed with hinges so that they could be raised when maintenance or cleaning of the channels was done.

Both the thermal barrier and the covers for the channels protected the workers from high thermal radiation. The sheet on the radiation side of the thermal barrier was very hot, but the sheet on the workers' side was much cooler. The difference between the temperature reading of a globe thermometer with and without the thermal barrier for an exposure period of one hour was about 40°C. The barrier as well as the channel covers acted as guards against splashes of metal, sparks, etc. The risk of accidents was greatly reduced.

The cost of the thermal barrier with the stands was estimated to be about US$ 40 and the cost for each cover for the slag channels was estimated to be US$ 15, including the labour cost. However, scrap materials and the spare time of a permanent employee were used. The maintenance cost was negligible.

Figure 77: Side view of an adjustable thermal barrier for portable use.

Figure 78: Front view of a portable heat barrier.

Figure 79: Covers over channels for molten slag. A globe thermometer measuring the heat radiation is seen.

Case 47: Use of longer tongs to reduce heat stress

A blacksmith shop in an engineering factory in Burma was using a forge hammer machine for production of square rods (dog spikes). The workers engaged in heating rod pieces near the machine complained of discomfort due to heat from the furnace. The production target of 2,000 hammered dog spikes per eight-hour shift could not be met.

Out of the five workers engaged in the process, only three were found to be close to the heat source. One of them had to put the rods into the furnace, while another picked the hot rods out of the furnace. This second worker was found to be suffering the most from the heat. The third worker who retrieved the dog spikes from the hammering machine to drop them into water for cooling was exposed in a limited manner. The radiant heat in the proximity of the furnace was 46°C. The tongs used by the two workers at the furnace were found to be 55 cm long. Work was interrupted repeatedly by demands for rest.

Figure 80: Furnace workers using short tongs. Putting a rod into the furnace.

The tongs were replaced by longer ones measuring 80 cm in order to move the worksite as far as possible from the furnace. The weight and the holding force of the tongs were considered carefully so as to avoid new problems. The radiant heat load measured at the work position was found to be 6°C less than in the previous work positions. The longer tongs were produced from ready stock in the factory and did not cost anything.

Parallel to this, a new work regimen was introduced for the heat-exposed work. Two more workers were added to the existing three, and three out of the five workers worked at a time while the other two rested in a cooler area in the shop. This was made possible by approximately US$ 50 per month, the current cost of employing two more persons. This led to an average increase of 60 per cent in the production, and the production target of 2,000 dog spikes per shift was achieved. There was consensus that thermal load was substantially reduced.

Figure 81: Short tongs previously used and long tongs used after the improvement.

Figure 82: A worker using longer tongs to take out a heated rod from the furnace.

Case 48: Insulation slab in front of furnace doors

The smith shop of a railway workshop in India employed 20 workers who were exposed to radiant heat emanating from furnaces. Some adverse effects were noted on the health and efficiency of these workers. At their place of work, the mean difference between readings of a thermometer and a dry bulb thermometer was as high as 46°C. These measurements proved that the workers were put under undue physiological stress due to excessive heat radiation. The workload as evaluated from the pulse rate and the sweating rate of the workers was categorised as “heavy”.

A 90 × 120 cm calcium silicate slab 50 mm thick was placed, as an insulation slab, at a fixed distance of 1.7 metres from the furnace doors. The slab served as a thermal barrier preventing heat radiation from the furnace doors from reaching the workers directly. There was remarkable relief in thermal strain. The pulse rate increase during work reduced by 40 to 70 per cent. The rate of perspiration also reduced by 20 to 30 per cent. The reduction in mean globe thermometer readings was from about 40 to 50 per cent.

The direct cost for fabrication of a set of a calcium silicate slab barriers with a frame was approximately US$ 180.

Case 49: Reducing heat stress by environmental improvements and protective clothing

In a small enterprise in Sri Lanka producing activated carbon, there were 12 workers employed in the kiln section. The process involved the burning of coconut shells and husks. The workers often complained of severe headache, a burning sensation in the eyes, nose and mouth, a hot feeling in the body, body aches and dryness of the skin. The kiln was made of cast iron and fired by diesel oil. There were openings at either end for loading and unloading.

The temperature was found to be often over 41°C, which was very hot, and humidity was also very high. Both ends of the kiln were so hot that the workers could not bear to be there for more than a few minutes at one time.

The problem was solved with a series of simple and inexpensive measures. The whole kiln was painted with white aluminium paint, which reduced the amount of radiant heat. A small wooden cubicle with tinted glass windows was constructed at a short distance from the kiln. The workers were told to stay in the cubicle except during the brief moments when they tended the kiln. In this way they avoided unnecessary heat exposure. When the workers tended the kiln, they wore aprons lined with aluminium foil on the outside and cotton on the inside. They also used tinted glass goggles. This insulated them from much of the heat. Drinking water containing some common salt was provided in the cubicle and the workers were encouraged to drink this frequently. This ensured that the workers had enough water and salt to replace that lost through perspiration. In addition, wire mesh was installed in the windows of the building in which the kiln was located. The windows could now be kept wide open the whole time, whereas previously they were kept closed for security reasons. This meant that general ventilation was improved.

All the above-mentioned environmental improvements led to a drop in the usual temperature around the kiln from over 41°C to about 36°C. The humidity was also reduced. The workers also complained less frequently of discomfort. By staying in the cubicle most of the time and using protective clothes when tending the kiln, they significantly eliminated the health hazard.

The direct cost of the improvements amounted to about US $400. The indirect costs, including the workers' time painting the kiln and building the cubicle, amounted to about US$ 80.

Case 50: Use of insulation material to dampen noise

In a small jewellery factory in Thailand, the noise produced by gem polishing machinery, which operated both day and night, was irritating and caused loss of sleep both for the workers who slept in a dormitory on the premises and for the residents living around the factory.

The gem polishing machinery consisted of a tumbler driven by an electric motor in which rough stones were placed with an abrasive mixture.

Casings for the tumblers were constructed from foam insulation material about 3 cm thick intended for refrigeration purposes and held in place by wire. Each casing cost about US$ 4. The cost of the time spent was minimal. Several trials had to be conducted to determine the thickness of foam required.

As a result, the noise level reduced substantially. The workers who slept in the dormitory reported that the noise was now tolerable. Although an increase in productivity was not measured, it could be surmised that workers were in a better state to work as they slept better.

While the improvement was inexpensive and easy to carry out, patience was needed, as the optimum thickness of insulation was found out only after several trials.

Case 51: Reducing noise by distance

In Sri Lanka, it was found that five power presses in a manufacturing enterprise produced noise levels of 102-104 dB(A). Even when only one or two presses were functioning, noise levels of up to 98 dB(A) were produced. This caused irritation to the workers and also the danger of noise-induced hearing loss.

To cope with this problem, the power presses were moved to a distance of 20 metres from the place where most of the workers were located. In this way, these workers were exposed to acceptable noise levels of 75-80 dB(A). Workers who operated the power presses were provided with ear muffs and rotated to a quieter section of the factory after a maximum of four hours continuous duty in the power press area.

This is an example of a low-cost solution to reduce noise to a safe and acceptable level simply by moving the noisy machines further away from most of the workers. The minority of workers who looked after those machines used ear protectors.

Case 52: Reducing noise by dampeners

In a factory in Thailand, plastic moulding machines produced excessive noise. In this case, noise dampeners were used to solve the problem. Shaped corks were fitted around escape valves from which most of the noise came (Figure 83). To protect the fragile corks, acrylic plastic caps were placed over them (Figure 84). These measures for each machine cost only a few US dollars but the noise levels reduced from more than 85 dB(A) to less than 60 dB(A).

In a small electronics factory in India, loud noise coming from a grinder was disturbing all the workers in the workroom. It was found that the direct mounting of the grinder on a wooden table made the noise much louder than expected. The grinder was without any cover for its power-transmission belt. Rubber dampeners were placed at the base of the grinder. The moving belt portion was covered with a metal cover which was also fixed using the rubber dampeners. The noise was greatly reduced and the workers could now communicate with ease while the grinder was in operation. The mounting of rubber dampeners, together with the belt cover, cost about US$ 18.

Figure 83: Cork silencers to reduce noise around escape valves.

Figure 84: Silencers with acrylic covers.

Case 53: An acoustic box functioning as a noise muffler

A compression process using an ultra-sonic engine was producing loud and sharp noise in a cassette tape recorder and radio factory in Indonesia. The compression process was necessary to fix glass to the main case plate of the front cover of each radio set. The workers manning this compression process were placed in a separate room so that the noise did not disturb other workers. The noise was as high as 105 to 107 dB(A) and thus a severe occupational hazard to the compression process workers, who carried out this process 500 times per work day.

An acoustic box was made using 16 mm particle board. The box was 96 cm long, 82 cm wide and 137 cm high. The inner part of the box was lined with noise-absorbing materials. Both the left and right sides of the box were furnished with a window and a door. The front part could be opened only when the compression process was finished. The ultra-sonic engine was put into the acoustic box.

Figure 85: An acoustic box encasing a noisy compression process. The inner part is lined with noise-absorbing materials.

The box was made by the company workers. The box materials cost US$ 70 for the particle board and US$ 48 for the acoustic materials.

The noise reduction was remarkable. With the box, the noise level fell to the range of 80 to 90 dB(A). The sound coming out of the box was no longer sharp. Other workers, when necessary, could work in the same room. The workers doing the compression process no longer felt isolated.