Safeguarding your machine
In the early days of the industrial revolution, labour was cheap and there was little regard for pain and suffering of injured workers. In more recent times, we have evolved through changes in social attitudes, placing more value on people who work with machines. These changes ensure that we continue to develop safeguarding measures for existing and new machinery. The challenge is to continue to improve the existing safety of machinery and also, as we make advances in technology, any new hazards need to be managed in a way that aligns with what is expected from the modern-day employer.
Pressures of a global playing field and different levels of the value on people (in the global market) make it even more challenging for the modern-day engineer. Whether designing, producing or maintaining, the engineer is faced with more and more complex machinery that requires increasing levels of protection and existing machinery that needs to comply with the relevant laws, regulations and standards of the day.
Sounds challenging - well fear not, there are well tried principles and processes that have been developed through regulations and standards which support current-day legislation. The overriding safety principle when designing any safeguards for machinery and plant is that safe operation without risk to the health of the operators must be ensured. Experience shows that the most cost-effective way to achieve this is to consider the potential risk of exposure to hazards during the design phase. This will enable the designer to design out any exposure to hazards, taking into account the need to reduce speed, temperature and pressure to an acceptable level. The same applies for existing machinery; we need to design a system that also complies with current-day legislation.
The first step is to understand the laws, regulations and standards. The new national harmonised OHS laws promised to remove confusion and provide a transparent national legislative framework for industry to follow. Currently, there are four states that are yet to enact the changes; Tasmania has the Bill before parliament, South Australia and Western Australia have no legislative action, while Victoria is likely to delay until 1 January 2013. Harmonisation will happen, it’s just a question of time for the federal government to provide the necessary concessions to enable the states to work towards passing the Bill.
Then there are the regulations and codes of practice that point us towards Australian Standards that will ensure we have designed and selected the correct interlocking system based on the risk of exposure to the hazard.
The law requires we eliminate risk and if this is not possible, then use engineering means. Guarding as a measure to control risk is an engineering means as described in the code of practice for plant. Therefore, the law requires that when access is not required, permanently fixed guards should be used. The perfect example of a fixed metal guard is to weld it into position or a casing enclosing an electric motor.
If access is required during operation, maintenance or cleaning, we then need to provide a guard that is interlocked. An interlock guard is one that is movable or has a movable part. The movement of the guard interacts via a switch connected to the control system which prevents movement of the dangerous parts of the machine while the guard is opened.
There is still more that needs to be considered. Now that we have incorporated a switch, how do we know what switch to use or how to design the control system? This is where confusion sets in.
Lack of education is perhaps the reason. If we go back to the law it does not help, but if we go through the relevant codes of practice we will be directed to the standard AS4024.1 - 2006 Safety of machinery. This standard will provide you with the necessary guidance required when looking at your interlocking system. The standard is divided into six sections covering: safety principles, risk assessment, ergonomic principles, design parameters, ergonomics and displays (controls, actuators and signals). The standard incorporates both European (EN) and International (ISO) safety and design standards of best practice for machine guard safety.
What about a guard that is not welded and is not interlocked? Yes, that’s right, you can use a fixed barrier that is removable by use of tools but, please err on the side of caution when selecting this option as you need to ensure the tool is NOT in the possession of the operator. The other point here is the ‘what-if method’. What happens if the operator does not put the guard back into position? The answer is a potential to cause harm and injury due to the ability to run the machine without the guard fitted. Hence, the hierarchy of control through elimination, substitution and engineer control before we rely on administration control and personal protective equipment (human behaviour).
Operators never think unsafe, they attempt to perform their duties in an efficient manner and assume the guarding will protect them. One would ask why would an operator manipulate or bypass the very device introduced to protect them. The answers are varied, but generally it occurs through lack of ergonomics. If the guarding is annoying or has a bad design, then the willingness to manipulate is directly proportional to the benefit gained.
The point here is, where possible, we need to consider manipulation and ensure we make that as difficult as is reasonably practicable.
A recent five-year study in Germany found that 37% of injuries caused by machines were a direct result of a machine that had been manipulated. What’s even scarier, a further investigation found that of 8% of the manipulated machines, the operators were not even aware of the risk they were taking.
If physical guards are not suitable, the hierarchy of control then allows the use of presence-sensing systems such as safety light curtains, safety scanners and safety mats or bumpers. Even though presence-sensing systems are the last step in the hierarchy of control, they are very much the only solution when looking at frequent access. Certainly, when used correctly, they can offer considerable productivity improvements such as the ability to load and unload machines more efficiently by reducing time taken to open and close doors and remove potential hazards introduced through the use of physical barriers.
A great example of the use of presence-sensing systems is on entry and exit of palletisers by using muting sensors to differentiate between products and humans.
Using captive key-type systems, there is a problem of trailing, where an operator can follow another operator into the machine danger zone through the physical gate without applying a tag or using the captive key system. This problem can be prevented by using a safety scanner to monitor if the operator is in the danger zone of machine, avoiding unexpected start-up. Safety scanners are also used on automated guidance vehicles (AGVs) as a solution against anti-collision and for personnel protection.
Preventing unexpected start-up
With all the above in mind, how do you know what method to use? When designing a machine, the possible risks shall be analysed and, where necessary, additional protective measures shall be taken to protect the operator from any hazards that may exist. To aid the machine manufacturer with this task, the standards define and describe the process of risk assessment. A risk assessment is a sequence of logical steps that permit the systematic analysis and evaluation of risks. The machine shall be designed and built taking into account the results of the risk assessment. Where necessary, risk reduction follows a risk assessment by applying suitable protective measures. A new risk shall not result from the application of protective measures. The repetition of the entire process, risk assessment and risk reduction, may be necessary to eliminate hazards as far as possible and to sufficiently reduce the risks identified. A collective approach is most suited when working through the assessment; otherwise, what can happen is the engineering department designs a safety system that complies, but they have not considered the requirements of the operators of the machine, generally around cleaning and maintenance. The end result is a system that on paper looks great and complies, but in a few weeks’ time the system is bypassed and manipulated because it was a hindrance to the operation of the machine.
The risk assessment process
The requirements on the protection of machinery have changed more and more with the increasing use of automation. In the past, safety systems were mostly a nuisance; for this reason they were often not used at all. Innovative technology has enabled protective devices to be integrated into the work process. As a result, they are no longer a hindrance for the operator and they often even help productivity.
Decision makers in industry are responsible for their employees, as well as for smooth, cost-effective production. Only if management make safety part of their everyday business, will the employees embrace the subject. To improve sustainability, experts call for the establishment of a wide-ranging “safety culture” in the organisation; after all, nine out of 10 accidents are due to human error.
The last point to note is, it is very important that the needs of operators and maintenance personnel are included in the planning at concept level. Only an intelligent safety concept matched to the operator task and the personnel will result in the necessary acceptance.
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