Safeguarding of Machinery

There are many types of guards we use in the industry to protect our people from injuries. As we know lots of incidents, we face on job site leading to loss of time, permanent disability to the injured person and loss of company reputation which can lead to loss of businesses in future.

Here we shall discuss the types of fixed guards we see on the job site in detail to understand the use and benefits of them.

Fixed Guards

There are three types of fixed guard:

1. Fixed Enclosing Guards, 

2. Perimeter Fences, and 

3. Fixed Distance Guards.

1. Fixed Guards:

Fixed guards have no moving parts and are fastened in a constant position relative to the danger zone. they are kept in place either permanently by welding, or by means of fasteners making removal/opening impossible without using tools.

If by themselves, or in conjunction with the structure of the equipment, they enclose the dangerous parts, fixed guards meet the requirements of the first level of the hierarchy.

Fixed enclosing guards, and other types of guard, can have openings provided that they comply with appropriate safe reach distances.

Fixed guards afford a number of benefits in that they are relatively cheap to design fabricate and fit; require minimal maintenance; are easy to monitor through visual inspection; can protect against hazards other than moving parts.

Potential concerns include inconvenience where frequent access is required for material feeding, maintenance, adjustment or lubrication, likelihood of removal, machine is able to operate without guard in place, may obstruct view of operation. 

2. Perimeter Fencing:

A perimeter fencing/guard is a fixed guard, which does not completely enclose the hazard, it is therefore recognised as being lower in the hierarchy.

Conventionally, perimeter fencing is made from 1.8m high, rigid panels securely fastened to the floor or to some convenient structure and positioned so that it is not possible to reach any dangerous parts of the machinery. it should only be possible to remove fixed fencing with the aid of a tool.

Where regular access is required, the fencing may be provided with sliding or hinged interlocked access gates, or an opening protected by a trip device.

Where is foreseeable that the normal access opening is either not large enough or is inconveniently placed for maintenance work, sections of the fencing may be made demount able, providing they can be removed only with the aid of a tool.

Temporary fencing may be used where it is required to provide a short-term safe area within a guarded enclosure and must be: of suitable height and prevent access to continuing dangerous movements, of stable and robust construction, interlocked with the appropriate part of the safeguarding system and used in conjunction with a safe system of work.

3. Distance Guard:

Where access to dangerous parts is limited to one aperture e.g., needed for feeding material into a machine a distance guard such as a "swan neck" or tunnel guard may be used.

Distance guards are designed to allow the feeding of materials into the machine whilst ensuring that workers cannot reach the dangerous parts.

Anthropocentric tables are utilised to ensure that the reach distances will protect 99% of the working population exposed.

Where access is required for cleaning or lubrication distance guards may be hinged with interlocking devices provided to ensure that the machine stops should the guard be moved.

4. Other Guards or Protection Devices:

Within each level of the hierarchy, there may be some choice available. In particular, the second level in the hierarchy allows a choice from a broad range of guards and protection devices.

"Other guards" include movable guards, adjustable guards, self-adjusting guards and automatic guards. all guards are physical barriers that prevent access to the danger zone.

Protection devices are devices which do not prevent access to the danger zone but stop the movement of the dangerous part before contact is made. they will normally be used in conjunction with a guard. Typical examples are mechanical trip devices, active opto-electronic devices such as light curtains, pressure sensitive mats and two-hand controls.

Where frequent access is required, it may be necessary to choose between an interlocking movable guard and a protection device. the choice of guard or protection device should be made subject to an effective risk assessment. the chosen device must be suitable for its purpose and afford an acceptable level of safety.

5. Interlocking Guards:

An interlock connects a guard and the control or power system of the machinery to which the guard is fitted.

The interlock and guard should be designed to ensure that:

Until the guard is closed the interlock prevents the machinery from operating by interrupting the power supply and either the guard remains locked until the risk of injury from the hazard has passed or opening the guard causes the hazard to be eliminated before access is possible.

Interruption of the power supply may be sufficient to eliminate the hazard before access is possible. Where the hazard cannot be eliminated immediately in this way the interlocking system will require a guard locking (time delay) or a braking system.

Interlocking may be achieved using electrical, mechanical, hydraulic or pneumatic media. Electrical interlocking, particularly in control systems, is the most common and electrical components are often incorporated in hydraulic and pneumatic circuitry.

Methods of interlocking which ensure that the power supply is interrupted when a guard is open fall into two groups:

a)     Power interlocking, where the interlocking device directly interrupts the power supply; and

b)     Control interlocking, where the interlocking device indirectly interrupts the power supply via a control system.

The interaction of the guard and its interlocking device can be arranged in two main ways:

Interlocking guard, where the movement of the guard operates the interlocking device; and interlocking guard with guard locking, where the interlocking device has to be moved to the off position before the guard can be opened.

These techniques can be used on power and control interlocking:

The simplest and least reliable interlocking systems are single-control systems, employing an interlocking device which indirectly interrupts the power medium by operating a single device via a control circuit. If that device falls the whole system falls to danger. There are many designs of switches used for interfacing guard movement with an on/off electrical control signal, including.

Cam-Operated Position Switches.

Tongue-Operated Switches.

Captive Key Switches.

Trapped Key Interlocking of Electrical Switches

Inductive Proximity Switches.

Magnetic Switches.

Plug and Socket Systems.

Manually Operated Delay Bolts; and

Solenoid Operated Shot Bolts.

Components and interconnections usually adopt one of two conditions on failure, e.g., open or closed circuit, on or off, engaged or disengaged.

Reliability of the system can be improved by designing switches that are less likely to fail to danger.

Position switches used for interlocking can be installed in either of two different modes, positive or negative. In the positive mode, the switch is operated by the direct operation of opening the guard. In the negative mode, closing the guard depresses the stem, when the guard is opened spring pressure is relied upon to open the switch contacts.

Negative mode devices are more likely to fail to danger as a result of seizure, spring failure, or contact welding they are also easily defeated by holding down the stem or lever while the guard is open.

There are a lot to talk but I am finishing this here and please feel free to share your fruitful comment on the above topic.