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Saturday, 12 March 2011 17:34

Physical Safety Hazards

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Climate, noise and vibration are common physical hazards in forestry work. Exposure to physical hazards varies greatly depending on the type of work and the equipment used. The following discussion concentrates on forest harvesting and considers manual work and motor-manual (mostly chain-saws) and mechanized operations.

Manual Forest Work

Climate

Working outdoors, subject to climatic conditions, is both positive and negative for the forest worker. Fresh air and nice weather are good, but unfavourable conditions can create problems.

Working in a hot climate puts pressure on the forest worker engaged in heavy work. Among other things, the heart rate increases to keep the body temperature down. Sweating means loss of body fluids. Heavy work in high temperatures means that a worker might need to drink 1 litre of water per hour to keep the body fluid balance.

In a cold climate the muscles function poorly. The risk of musculoskeletal injuries (MSI) and accidents increases. In addition, energy expenditure increases substantially, since it takes a lot of energy just to keep warm.

Rainy conditions, especially in combination with cold, mean higher risk of accidents, since tools are more difficult to grasp. They also mean that the body is even more chilled.

Adequate clothing for different climatic conditions is essential to keep the forest worker warm and dry. In hot climates only light clothing is required. It is then rather a problem to use sufficient protective clothing and footwear to protect him or her against thorns, whipping branches and irritating plants. Lodgings must have sufficient washing and drying facilities for clothes. Improved conditions in camps have in many countries substantially reduced the problems for the workers.

Setting limits for acceptable weather conditions for work based only on temperature is very difficult. For one thing the temperature varies quite a lot between different places in the forest. The effect on the person also depends on many other things such as humidity, wind and clothing.

Tool-related hazards

Noise, vibrations, exhaust gases and so on are seldom a problem in manual forest work. Shocks from hitting hard knots during delimbing with an axe or hitting stones when planting might create problems in elbows or hands.

Motor-Manual Forest Work

The motor-manual forest worker is one who works with hand-held machines such as chain-saws or power brush cutters and is exposed to the same climatic conditions as the manual worker. He or she therefore has the same need for adequate clothing and lodging facilities. A specific problem is the use of personal protective equipment in hot climates. But the worker is also subject to other specific hazards due to the machines he or she is working with.

Noise is a problem when working with a chain-saw, brush saw or the like. The noise level of most chain-saws used in regular forest work exceeds 100 dBA. The operator is exposed to this noise level for 2 to 5 hours daily. It is difficult to reduce the noise levels of these machines without making them too heavy and awkward to work with. The use of ear protectors is therefore essential. Still, many chain-saw operators suffer loss of hearing. In Sweden around 30% of chain-saw operators had a serious hearing impairment. Other countries report high but varying figures depending on the definition of hearing loss, the duration of exposure, the use of ear protectors and so on.

Hand-induced vibration is another problem with chain-saws. “White finger” disease has been a major problem for some forest workers operating chain-saws. The problem has been brought to a minimum with modern chain-saws. The use of efficient anti-vibration dampers (in cold climates combined with heated handles) has meant, for instance, that in Sweden the number of chain-saw operators suffering from white fingers has dropped to 7 or 8%, which corresponds to the overall figure for natural white fingers for all Swedes. Other countries report large numbers of workers with white finger, but these probably do not use modern, vibration-reduced chain-saws.

The problem is similar when using brush saws and pruning saws. These types of machines have not been under close study, since in most cases the time of exposure is short.

Recent research points to a risk of loss of muscle strength due to vibrations, sometimes even without white finger symptoms.

Machine Work

Exposure to unfavourable climatic conditions is easier to solve when machines have cabins. The cabin can be insulated from cold, provided with air-conditioning, dust filters and so on. Such improvements cost money, so in most older machines and in many new ones the operator is still exposed to cold, heat, rain and dust in a more or less open cabin.

Noise problems are solved in a similar manner. Machines used in cold climates such as the Nordic countries need efficient insulation against cold. They also most often have good noise protection, with noise levels down to 70 to 75 dBA. But machines with open cabins most often have very high noise levels (over 100 dBA).

Dust is a problem especially in hot and dry climates. A cabin well insulated against cold, heat or noise also helps keep out the dust. By using a slight overpressure in the cabin, the situation can be improved even more.

Whole-body vibration in forest machines can be induced by the terrain over which the machine travels, the movement of the crane and other moving parts of the machine, and the vibrations from the power transmission. A specific problem is the shock to the operator when the machine comes down from an obstacle such as a rock. Operators of cross-country vehicles, such as skidders and forwarders, often have problems with low-back pain. The vibrations also increase the risk of repetitive strain injuries (RSI) to the neck, shoulder, arm or hand. The vibrations increase strongly with the speed at which the operator drives the machine.

In order to reduce vibrations, machines in the Nordic countries use vibration-damping seats. Other ways are to reduce the shocks coming from the crane by making it work smoother technically and by using better working techniques. This also makes the machine and the crane last longer. A new interesting concept is the “Pendo cabin”. This cabin hangs on its “ears” connected to the rest of the machine by only a stand. The cabin is sealed off from the noise sources and is easier to protect from vibrations. The results are good.

Other approaches try to reduce the shocks that arise from driving over the terrain. This is done by using “intelligent” wheels and power transmission. The aim is to lower environmental impact, but it also has a positive effect on the situation for the operator. Less expensive machines most often have little reduction of noise, dust and vibration. Vibration may also be a problem in handles and controls.

When no engineering approaches to controlling the hazards are used, the only available solution is to reduce the hazards by lowering the time of exposure, for instance, by job rotation.

Ergonomic checklists have been designed and used successfully to evaluate forestry machines, to guide the buyer and to improve machine design (see Apud and Valdés 1995).

Combinations of Manual, Motor-Manual and Machine Work

In many countries, manual workers work together with or close to chain-saw operators or machines. The machine operator sits in a cabin or uses ear protectors and good protective equipment. But, in most cases the manual workers are not protected. The safety distances to the machines are not adhered to, resulting in very high risk of accidents and risk of hearing damage to unprotected workers.

Job Rotation

All the above-described hazards increase with the duration of exposure. To reduce the problems, job rotation is the key, but care has to be taken not to merely change work tasks while in actuality maintaining the same type of hazards.

 

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