Risk assessment is as vital as it ever was in maintaining machine safety, writes Greg Pitcher.
There can be a perception that machinery in the process sector is perhaps not as dangerous as some of the equipment used in certain other industries. But this outlook in itself poses a danger.
“You can be at a sugar refinery where the vast majority of plant is process equipment – a lot of pipework but not a great deal of moving machinery – but at the back end are palletisers and bagging machines,” says David Main-Reade, business development consultant for safety and sensing at Rockwell Automation.
This hybrid model makes it easy for hazards to go undetected or incorrectly mitigated.
You need to spend more time at the concept stage to design a machine properly, because incorrect specification will flow through to a machine that is built but can’t be used properly
David Main-Reade, business development consultant, Rockwell Automation
“If you approach the whole plant from a [process-style] hazard and operability study perspective, quite often you can get into a bit of difficulty,” says Main-Reade. “But equally, with a machinery hat on, you can miss some process hazards.”
Schmersal UK carries out risk assessments on a variety of process industry machinery.
Applications engineer Mark Langfield says: “We deal with machines from small lathes to big hydraulic presses.
“A variation of things can go wrong – you risk entanglement, severing of limbs, electrocutions.”
Saving lives
An HSE study in 2003 looked at the causes of a number of incidents including a gas release from a chemical plant; a mis-read VDU screen which led to an acid spillage; and a man being crushed to death by a food factory hoist.
The study found that 44% of incidents analysed had been caused by poor control system specification.
“The control system needs to be continually reviewed throughout all lifecycle phases, both from the perspective of the equipment under control and the detailed design and implementation of the control system itself,” said the report.
“Otherwise the end result is a machine, or plant, with inadequate protection against the hazard.”
Main-Reade agrees that it is critically important to get machine specification correct. “You need to spend more time at the concept stage to design a machine properly, because incorrect specification will flow through to a machine that is built but can’t be used properly, meaning end users bypass the safety mechanisms and expose themselves to risk,” he says.
Setting goals
Main-Reade believes a key element to ensuring machines are correctly specified is getting the standards they have to adhere to right.
He sits on two International Electrotechnical Commission committees, looking at the technical aspects of design standards for machine control systems.
“TC 44 is in the process of drafting IEC 62061 for electrical, electronic and programmable electronic control systems.
“I’m also on TC 199, which is revising ISO 13849 part one – safety requirements for parts of control systems – with the goal of pulling the two standards together.
“At the moment machine builders can choose which one they conform to and we’re trying to get them to be closer together so there are fewer gaps to fall through. I have seen people trying to use the wrong standards, so a machine that should be safety integrity level 3 is only SIL1.”
The technology available now is improving safety, particularly with electronic safety devices that are almost self-monitoring
Mark Langfield, applications engineer, Schmersal UK
Main-Reade says designing safety measures that enhance productivity is a key way of embedding good practice. “Enterprise helps when it comes to safety – and we needed technology to allow that to happen. Machine builders are utilising these safety solutions to allow workers to be more effective in the envelope of the machine.”
Langfield agrees that technology has provided a boost to factory incident prevention. “The technology available now is improving safety, particularly with electronic safety devices that are almost self-monitoring,” he says. “They look similar to electro-mechanical devices but they are inherently non-contact.”
Schmersal offers a range of radio-frequency identification (RFID) electronic tools. “They monitor themselves, detecting faults in the safety system and giving early warnings,” says Langfield.
“For minor faults a device will send a signal to the safety system and – if it’s not a major fault – it will give 30 minutes’ warning that it will shut down the system.”
Fault factors
As well as giving process plant operators a chance to fix faults before they disrupt production – or worse, cause an incident – these smart devices can uncover faults that may have remained hidden under traditional systems.
“With older electro-mechanical devices you had the risk of fault masking if devices were in series. Another gate within a series could be opened and closed and mask the fault. With more modern technology, these faults are identified.”
Another area of technological advance is with safety logic controllers, some of which now come built-in.
“The SLC will monitor all the safety devices on a machine and, in certain circumstances, physically manipulate them,” says Langfield.
“They are becoming more integrated. At the upper end you have a programmable logic controller with on-board SLC. It gives end users flexibility.”
These shouldn’t act as a substitute for proper specification, though, warns Langfield. “A risk assessment is still required when a machine is designed, which will determine what safety functions are required, and what level of performance is required for each safety function.
“Risk assessments are the most important element of machine safety.”
On top of this, safety features need to be correctly installed for machine safety initiatives to work effectively. For advanced measures such as light curtain sensors [pictured above], correct positioning can be determined by a number of factors.
“If a light curtain is incorrectly positioned, then you could get to a moving hazard before it’s stopped, which is a potential danger,” says Langfield. “We recommend that machines are assessed every year because a stop time could alter.
“It is not complicated as long as you understand the standard and what you’re checking, and you have the equipment. The stop time measurement assessment is a simple procedure. It could be done a lot more than it is.”
Paul Taylor, manager for machinery safety at TUV SUD, says physical guarding retains an important role in keeping people safe from machines.
All the European-based legislation is enshrined and so will continue. It will be some time before we know the ramifications of Brexit
Paul Taylor, manager for machinery safety at TUV SUD
“If done correctly, this still takes some beating in terms of guaranteeing the safety of personnel,” he says. “The biggest problem with physical guarding is that at certain times, personnel have to go through them, and it’s these interventions that need to be considered and dealt with carefully.”
Use of technology is only going to increase, and could change the ways factories look and work in the future, Taylor predicts.
“Instead of having lots of physical guarding, operatives could wear a badge and if they went close to a machine, it would slow down or stop,” he says.
“Laser scanners can also be used in a similar manner. The increased use of robotics, either traditional or collaborative, could mean that people are taken away from more dangerous areas, with robots providing a safer conduit.”
Away from the world of gadgets, what do the uncertain political times hold in store for machine safety specialists?
“At least initially, nothing will change from a legislative perspective,” insists Taylor. “All the European-based legislation is enshrined and so will continue. It will be some time before we know the ramifications of Brexit.”
The British Standards Institute says it expects the UK to continue to participate in the European standards system as a full member of European bodies CEN and CENELEC post-Brexit.
“From a practice point of view, it’s more than likely that EN standards will remain in place,” says Taylor.
