POWER DRIVEN MACHINERY HAZARDS

 Power-driven machinery

 Hazards

The use of power-driven machinery on construction sites involves many hazards. Common to many construction machines are in-running nip points where one part rotates against or close to another. Common examples are cog-wheels, chain and sprockets, belts and cylinder drums, and ratchet drives. All nip points should be assumed to be dangerous and should be guarded to prevent approach unless they are enclosed within the machine. Equally dangerous are rotating shafts of whatever diameter and of whatever speed. A common cause of the accident is clothing becoming caught and wrapped around the shaft. If the shaft is not inaccessible within the machine frame, then it must be enclosed – a loose tube covering and resting on the shaft is a cheap, convenient and effective method.

Safety precautions

When you use power-driven construction tools and machinery, make it your regular practice to check whether:

– all protective devices and safety measures supplied with the machine are in position, adjusted and working;

– the machine appears to be safe to use even for an inattentive worker;

– safety devices are strong enough to withstand wear from ordinary use; and

– safety devices do not prevent efficient use of the machine.

If you are not satisfied on any of these points, discuss them with your supervisor.

Point to remember:

• A dangerous part of machinery requires a guard – a warning notice is not a substitute.

 Circular saws

Among the most dangerous power-driven machines found on a construction site is the circular saw, mounted in a bench and used for ripping, deep-cutting or cross-cutting. The main causes of accidents are:

– hands coming into contact with the saw blade either above or below the bench;

– timber being thrown back by the revolving blade;

– the blade fracturing or disintegrating.

The top of the blade should be covered by a form of hood which is designed to prevent your hands touching the part of the blade above the wood being cut. It should be adjusted at the front or leading edge of the saw so that it almost touches the surface of the material being cut, leaving no space for a hand to pass through. Behind the blade, and set not more than 12 mm from it at bench level, should be fitted the device called the riving knife. This prevents the cut closing on the back of the blade causing the material to be thrown back at the operator. These features are shown in.

Parallel to the blade is the fence which acts as a support and guide for the wood being sawn and allows a true cut to be made. It should be locked securely in position before the cut is made.

When the hand-feeding material to the saw blade, use a push-stick to keep your hands away from the blade. Use the push-stick also to remove the cut pieces from between the blade and the fence and to remove offcuts from the bench. When you are ripping long lengths of material, they should be supported as they come off the table.

Always keep the saw teeth sharp and properly set. A dull blade is much more likely to break than a sharp one. Never use a blade which is defective in any way.

Compressed air tools

If air under compression is allowed to penetrate the skin through a scratch, it can cause painful swelling and may result in serious damage if directed at the eyes, nose or ears. The most common cause of accidents with compressed air is its use to dust off clothing at the end of a working shift. There are also serious injuries caused by workers directing compressed air at a colleague in horseplay.

Cartridge-operated tools

Cartridge-operated tools, which are used for direct fixing to concrete, brick and steel, should be fitted with a guard which does not

Points to remember:

• Never leave the saw running after you have used it.

• Always keep the push-stick at the table.

• Never start cleaning above or under the table until the blade has stopped.

Allow the tool to be fired until the guard is accurately positioned against the work.

Head and eye, and hearing protection should always be worn. The area around the fixing should be cleared of workers in case the material splinters or there is a rejection or a ricochet of the fixing. Firing against too soft or thin material may allow the fixing to penetrate it and injure someone on the opposite side.

The recoil from firing the tool may cause the operator to lose balance – it should never be used from a ladder.

Discussion

• What are the risks associated with power-driven machinery? What would you do to minimize these risks?

• What safety devices would you expect to find on a circular saw, and what is their purpose?