Australian OHS Acts stipulate that both hazard identification and risk assessment must be carried out to identify and minimise risk; and yet, every year, people are injured and even killed by machinery while at work.
Safety controls play an integral part in preventing the risk of injury from various hazards that inevitably exist in the workplace. Hazards that are likely to cause injury or, in the worst-case scenario, death must be eliminated or dealt with by putting controls in place to reduce the risk.
One typical hazard in the workplace is poor machine-guarding practices. Exposure to dangerous machine parts during operation, examination, adjustment and/or maintenance can pose many serious risks.
However, there are various safety products and controls available that when installed correctly, and in conjunction with appropriate monitoring devices, will go a long way towards preventing injuries.
If the risk cannot be eliminated, it must be minimised which can be achieved through a three phased approach:
- Understanding the risks
- Evaluating the risks
- Implementing the right solutions to reduce the risks
The process to determine the needs of a complete safety system goes back to understanding the risks or hazards that could result in injury.
A common misunderstanding when it comes to the use of individual safety control components, such as safety switches, gate/guard interlocks and light curtains, is that they alone are capable of offering a complete, safe system of control.
Safety systems comprise many components and no individual component, in isolation, will ensure the complete integrity of any safety control system.
It is often necessary to involve specialist safety consultants to perform a safety audit. These consultants will produce a report detailing any shortcomings and the recommended changes necessary to meet OH&S requirements.
Safety audits can also provide an understanding of the level of risk, as well as information on a suitable safety system, or improvements, for your workplace. Additionally, the auditors will often return after the installation is complete to verify that the site or machine now meets safety requirements.
In order to reduce the risk, all machinery must be securely guarded to prevent access to dangerous parts. Machine guarding is vital to every workplace using machinery. It is also important to remember that machine guards do not have to be complicated nor interfere with productivity.
As mentioned, a safety interlock switch alone does not offer a complete safety control system. Safety control system installations require the evaluation of risk and hazards involved in line with the Australian standard AS4024.1 to establish the category of risk and the degree of protection that is required.
A risk graph (as shown on the left) can be used to help determine the risk category.
Almost every safety control system has the inclusion of an emergency stop (e-stop) switch. The e-stops of today have come a long way from the earlier, more simple designs, and now include multiple contacts with a force-guided mechanism to prevent failure due to contacts sticking or welding.
For example, a new range of Electroslim safety interlock switches also incorporates a manual key for locking and unlocking – a quality not previously available in safety switches.
The lock/unlock feature can add to the protection of workers by limiting the risk of accidental machine starts while personnel are carrying out maintenance and commissioning works on their plant machinery.
Safety trip wire switches offer similar features to an e-stop but use a fixed-wire rope which is connected from one end of the machine to the other.
These safety trip wire switches can be triggered anywhere along the machine and allow access where an individual emergency safety switch may not be accessible.
Safety trip-wire switches also trigger in the event of the trip wire breaking. It is important that all electrical equipment be installed, operated, serviced and maintained by qualified personnel who are well trained and experienced in safety system requirements and standards implementation.
[Paul Morton is Product Manager – Sensors, Industry Business, Schneider Electric.]