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Light Curtains for machine guarding

 

When designing a guarding solution for plant, the designer must ensure that the chosen guard is fit for the application and meets the relevant regulations and standards. It is not a case of just adding a guard – considerable thought must be put into design and selection to maximise both safety and productivity.

Part 1 - Selection of guard

Various state plant regulations list a hierarchy of guarding. For example, the Victorian Occupational Health and Safety Regulations 2007 state that:

3.5.4 Guarding 

(2)     If a designer of plant uses guarding as a measure to control risk, the designer must ensure that— 

a.       if access to the area of the plant requiring guarding is not necessary during operation, maintenance or cleaning of the plant, the guarding is a permanently fixed physical barrier; or 

b.       if access to the area of the plant requiring guarding is necessary during operation, maintenance or cleaning of the plant, the guarding is an interlocked physical barrier that allows access to the area being guarded at times when that area does not present a risk and prevents access to that area at any other time; or 

c.       if it is not reasonably practicable to use guarding referred to in paragraph (a) or (b), the guarding used is a physical barrier that can only be altered or removed by the use of tools; or 

d.       if it is not reasonably practicable to use guarding referred to in paragraph (a), (b) or (c), the design includes a presence-sensing safeguarding system that eliminates any risk arising from the area of the plant requiring guarding while a person or any part of a person is in the area being guarded 


The designer must ensure that any guards intended to provide protection from parts of the plant or work pieces that may break, disintegrate or be ejected are designed to contain effectively the parts, work pieces or any fragments of them.

This is very important when deciding what type of guarding solution is chosen. A presence sensing device would not be suitable if projectiles are foreseeable from the hazardous area (i.e. debris, fragments, broken tools etc.). A physical barrier would be required to contain the ejected parts.

It is crucially important to consider the stopping time of the hazard. If the hazard takes a long time to come to a stop (e.g. a rotating saw blade) then, again, a presence sensing system may not be suitable since the operator may be able to get access to the hazard before it has come to a complete stop.

Therefore, when selecting a guarding solution a question and answer sheet might look like this:

Q1. Is there a possibility of parts being ejected? For this example, no.

Q2. Does it take a long time for the hazard to stop? Again for this example, no.

Q3. Permanently Fixed Physical Barrier? No. 

Why not? Need access for maintenance and general machine operation. 

Q4. Interlocked Physical Barrier? Preferably not. 

Why not? Access within the danger zone is often required. An interlocked guarding solution may frustrate the operator who may in turn attempt to bypass the guarding system.

Q5. Physical Barrier requiring a unique tool or key ? No.

Why not? Frequent access may frustrate the operator and cause inefficiency, poor work performance and some resentment to this being a safety solution. This will most likely eventuate in the operator gaining access to a tool and removing the guard permanently.

Q6. Presence Sensing System (Light Curtain or similar) Yes.

Why? A light curtain will allow frequent access to the hazardous area without delays to the work process. There are no projectiles that could possibly come out of this machine; therefore, a light curtain can be a good guarding solution to maximize productivity as well as protecting operators and maintenance from the hazard, provided it is located correctly with maximum machine stopping time taken into account.

Each time any form of guarding is to be used, this hierarchy needs to be followed. The first consideration should be to completely isolate the area from humans (allowing no access) working down the list to administrative control and PPE as a last resort.


A light curtain/barrier has been decided as the guarding solution, but there is more work that is required to finalise the solution – what light curtain can be used?

In the next issue of the Pilz Australia Safety Update we will cover the second half of this article that will cover the selection criteria for the type of light curtain/barrier and also safety distances for the positioning of the light curtain/barrier.

For information on the Pilz range of light curtains and light barriers please click here: light curtains

This is a news item from Pilz Safe Automation in Australia. All the standards and directives described refer to Australia and may vary elsewhere.