Questioning the safety of handheld laser welding
Matthew Dale asks experts whether this emerging application poses any risks to the user
Since becoming the editor of Laser Systems Europe and having numerous conversations with experts regarding safety in laser materials processing, one message has been made abundantly clear: ‘Put it in a box.’
Now this phrase, while elegantly simple at first glance, doesn’t just refer to putting a laser in an enclosure or machine where the optical radiation can’t escape. It means putting an entire laser process into an enclosure armed to the teeth with interlocks, fume extraction technology, protective glass, bright LED signage, and backscatter sensors that detect as soon as the laser starts moving off-course.
Once the laser shuts off at the end of processing, only after the enclosure has been completely ventilated of tiny, cancerous, combustible particles, should a person actually be allowed to enter.
At first glance however, the relatively recent emergence of handheld laser welding equipment appears to contradict this strict ideology.
As an application, handheld laser welding promises a number of benefits including: low running costs; minimal set up requirements; ease of use; highly efficient, fast and flexible processing in spatially challenging environments; minimal consumables and post-processing requirements; and most importantly, high-quality welds of both similar and dissimilar materials of different types and thicknesses.
But to enable all this, a person must be in the room holding the laser, which violates the core principle of ‘Put it in a box’.
This certainly isn’t to say however that the manufacturers of these systems have thrown all safety precautions to the wind. On the contrary, looking around I can see many of these systems are equipped with safety features such as multi-trigger/pedal activation, active laser emission indicators, and contact sensors that shut off the beam as soon as the system moves away from the workpiece. With regards to safety enclosures, PPE and fume extraction, while most system manufacturers express the need for safety goggles when using their handheld laser welders, those also suggesting the use of equipment such as gloves, welding helmets, fire retardant clothing, barriers and fume extractors are by far in the minority.
This also isn’t to say however that those particular system manufacturers making little to no safety recommendations are at all in the wrong. As we find out later in this article, as long as these systems are sold as Class-4 lasers, the responsibility of their safe usage is passed entirely onto the customer.
However, regardless of the safety recommendations provided with the equipment, and regardless of the precautions taken when using it, as handheld laser welding still requires a person to be present in a ‘box’ with an exposed high-power beam, this presents a number of risks.
Consulting with the experts
To get an idea of these risks, I approached two experts who between them have decades of experience in laser safety.
My first contact is John Tyrer, a professor of optical instrumentation at Loughborough University and managing director of safety firm Laser Optical Engineering. He is: a frequent chair of the Laser Institute of America’s International Laser Safety Conference (ILSC); an organiser of Public Health England’s Laser Safety Forum; responsible for the high-power laser safety standards in the International Electrotechnical Commission (IEC); and a provider of laser safety training for 25 years.
Before our conversation even began, he referred me to clauses from the UK’s 2008 Supply of Machinery Safety Regulations, which he explained is derived from an EU directive.
1.5.12. Laser radiation
Where laser equipment is used, the following should be taken into account:
laser equipment on machinery must be designed and constructed in such a way as to prevent any accidental radiation
laser equipment on machinery must be protected in such a way that effective radiation, radiation produced by reflection or diffusion and secondary radiation do not damage health
optical equipment for the observation or adjustment of laser equipment on machinery must be such that no health risk is created by laser radiation
1.5.13. Emissions of hazardous materials and substances
Machinery must be designed and constructed in such a way that risks of inhalation, ingestion, contact with the skin, eyes and mucous membranes and penetration through the skin of hazardous materials and substances which it produces can be avoided.
Where a hazard cannot be eliminated, the machinery must be so equipped that hazardous materials and substances can be contained, evacuated, precipitated by water spraying, filtered or treated by another equally effective method.
Where the process is not totally enclosed during normal operation of the machinery, the devices for containment and/or evacuation must be situated in such a way as to have the maximum effect.
Tyrer noted that a handheld laser welding system is definitely considered machinery, and so should abide by the above regulations – at least in the UK and EU.
Potential hazards include: Fire, explosions, skin rashes and cancer
First off, Tyrer explored the common recommendation that goggles must be worn when using handheld laser welding systems. Goggles are worn because a laser beam is considered capable of damaging the eye if it is viewed closer than the calculated nominal ocular hazard distance (NOHD), where it would exceed the maximum permissible exposure (MPE) limit of the eyes set out by law. If the operator and any nearby colleagues are within the NOHD of the handheld laser welder, they must wear goggles to protect their eyes – not only from viewing the beam directly, but also from any reflected radiation.
‘When you see people use handheld welding equipment, they aren’t working perpendicular to a surface, they’re working at an angle,’ said Tyrer. ‘Now, if it's an approximately 1μm wavelength fibre laser, and it's welding steel, then it’ll exhibit around 50-60 per cent coupling. That means anywhere up to 50 per cent of the energy can be reflected off – even more in the case of a specular reflection. Looking at the scatter characteristics coming out from the workpiece, you get a very nasty cone of energy coming out that also contains a fair amount of the main beam. On some of these lasers, the NOHDs I've seen are in the range of metres up to tens of metres!’
In Tyrer’s eyes however, which you’ll never find covered with a pair of goggles (Loughborough University proudly went goggle-free in recent years), wearing safety eyewear around a materials processing laser doesn’t ensure anywhere even remotely close to complete protection. This is because, according to him, not only can many materials processing lasers penetrate goggles in a matter of seconds, but the reflected radiation from laser welding (and all laser materials processing for that matter) is capable of doing far much more than damaging the eye.
‘I look after the high-power laser safety standards in the IEC,’ he said. ‘We had a meeting recently between the conveners from different sectors, and in this meeting I warned that we’re seeing a big rise in these handheld systems. Others in the meeting pointed out that surely those around the equipment could simply put goggles on, and I had to say “No! It sets fire to everything – clothing, hair, even the fabric of the building itself”. I was told I was being reactionary and that they’ve been doing this for 30 years, but I brought up the fact that we haven’t had handheld lasers until recently. They said, “well, it won't be a problem, will it?“, and I had to say “how long do you want to wait before the first big explosion happens?”. The fume is going to consist of particulates. In aluminium welding for example this will be fine particulates of aluminium. In oxygen, these will ignite and up it will go. If you want to accelerate an explosion, you add fine particulates of aluminium.’
‘So this idea that you and anyone standing around watching can just wear a pair of goggles is ridiculous,’ Tyrer continued. ‘They might have a pair of goggles on, but their hair could suddenly catch fire, or their overalls will catch fire...I really am not messing around here you know! And if the Health and Safety Executive (HSE) gets called in due to such a fire, they won’t just shut down your handheld laser welding equipment, they’ll shut down every single laser machine your company owns, which could lead to huge profit losses.’
Fires and explosions aren’t the only risks associated with reflected laser radiation however. It was Tyrer himself who started working with the UK’s Health and Safety Laboratory (HSL) many years ago to conduct laser fume diagnostics and determine the dangers they pose when inhaled.
‘Let me give you an example,’ he said. ‘When you process stainless-steel with a laser, its chromium and nickel components are released as microscopic particles. If any of these metal vapours get on your hands, or any exposed skin for that matter, you’re risking contact dermatitis. This could lead to skin rashes on your arms and legs. Also, if inhaled, these fumes can kill you – not instantly, but in 10 to 20 years’ time, and in a very nasty way.’
Therefore it is key that dedicated laser fume extraction technology is used in an area where laser processing is taking place. Tyrer noted that he’s previously seen laser safety officers who believe they’ve installed proper fume extraction technology, but instead have turned out to just put big extractor fans in the ceiling of their laser enclosure. ‘All that does is drag the air out, rather than dealing with the harmful fumes themselves,’ he said. ‘Does a kitchen extraction fan remove all the smells when you’re cooking? No! The principle is the same with fume extraction in laser processing. Dedicated laser fume extraction systems are needed that remove all the microscopic particles from the air.’
With regards to how to determine when an area is safe for entry following laser processing, Tyrer said it’s right there in the governmental regulations of each country. ‘In the UK for example, only until an enclosure has been ventilated of hazardous materials and substances to the point where an employee won’t be exposed to levels above those set out in the HSE’s EH40/2005 Workplace exposure limits can a worker legally be allowed to enter.’
I therefore asked Tyrer: ‘So would it become safe if someone used a handheld laser welding system within a fully equipped, interlocked laser enclosure where a fume extraction nozzle is placed right next to the process, and where anyone inside is required to wear a welding helmet with infrared radiation protection, laser safety goggles, leather gloves and flame-retardant clothing covering all their skin?’
‘It wouldn’t make any difference!’ he remarked. ‘First of all, regarding the flame retardant clothing: This doesn’t mean it’s fire-proof, it means it is much harder to ignite. What will end up happening is the reflected radiation will still heat up the fire-retardant coating and continue to do so until it ends up being destroyed and the material gets ignited anyway. The hazard still hasn’t been dealt with, therefore this can’t be worn as PPE for this application. Secondly, regarding the fume extraction: I’ve done numerous fume analyses that have revealed that lethal, cancerous, combustible particles get ejected from welding processes in a scatter pattern so quickly that even if the nozzle is right next to them it has no chance of capturing them all. This is why an enclosure containing such an application needs to be cleared of these particles – to safe levels as governed by regulations – before anyone should be allowed to enter.’
My next contact is David Lawton, European market development manager for US laser safety equipment manufacturer Kentek. Between that and his previous role at UK laser safety firm Lasermet, he has over a decade of experience advising customers on laser safety.
‘Handheld laser welders without a doubt have a place, but they’re extremely dangerous,’ he began. ‘They enable flexible manipulation of a powerful beam over a workpiece and allow you to access areas you could never get a robot into, but there’s lots of lessons to be learned before they can be used safely.
‘First of all, in its current state the equipment itself will always need to be sold as a Class-4 laser device – it can't be sold as anything else. And so straight away, if you have one of these, you’ll need a laser safety officer, a laser protection advisor or a competent person, and you’ll need all the mechanisms and risk assessments that go along with it. You won’t be able to escape any of that.’
To put his points into context, Lawton ran me through the usual procedure of setting up a laser process safely.
‘The principles behind laser safety are actually quite simple,’ he said. ‘You create a laser controlled area, and then make sure that the radiation is contained within that area. Now, for a typical laser system, the laser-controlled area is inside the machine itself, with nobody able to gain access until the laser shuts off. In a lab in a university or a room in a production facility, the room itself can become the laser controlled area. You need safety windows or blinds/curtains, LED signage warning of the laser being active, and an interlock on the door linking to the laser. While someone can technically be inside this area (provided there is no risk of them being exposed to radiation levels/hazardous materials and substances exceeding the legal limits) the HSE is now driving more towards putting the whole process in an inaccessible enclosure. And I agree with this where it’s practicable.’
Handheld laser cleaning systems, which have also emerged in recent years, also present hazards that must be dealt with before they can be used safely. (Image: Shutterstock/Surasak_Photo)
Lawton then highlighted a particular challenge of laser welding that could increase the difficulty of ensuring personnel safety around a handheld system: ‘During the process you create a weld pool of molten material and move that along the weld seam. The problem is that molten material is a really, really, really good reflector. In addition, the weld pool is quite often quite spherical as well, or it's at least certainly not flat. So you've now got the chance of the beam bouncing off the weld pool in virtually any direction. Another issue is the fact that due to the excellent reflective properties of a weld pool, this bouncing could be in the form of a specular reflection rather than a diffused reflection, which means that anywhere up to 60-70 per cent of the energy that's coming in can come straight back out again. Once you reach kilowatt-level laser materials processing, to my knowledge no PPE exists that can protect you from such a specular reflection.’
At this point you may be wondering whether it is actually possible to use handheld laser welding equipment in its current state in compliance with UK and European safety regulations. With the number of factors involved however, this is a matter best left for the safety officers of manufacturing firms – and ultimately the HSE if they get called in – to decide.
Whether such equipment can be sold within UK and European regulations however is a far simpler matter. ‘As long these systems are always classified and sold as Class-4 laser devices then it’s completely legal for them to be sold,’ said Lawton. ‘This is because the onus of making it safe and using it safely is completely on the customer.’
He continued: ‘Whether it is possible to use them safely within regulations however...the risks of traditional handheld welding are huge as it is, now add in the additional risks of using a laser; welders will need to be told that this isn’t a traditional welder and that the radiation can be reflected away from the process area. These risks need to be managed in accordance with the regulations of the region they exist in. The simplest way to manage these risks is to turn the whole device into a Class-1 laser product. This then bypasses the requirement for any sort of risk assessment, any sort of safety training, the need for a laser safety officer or advisor, you just plug it in and go. That's why there is such a drive from customers and end users to have Class-1 laser products.’
During normal operation, a Class-1 laser product will never expose the user to anything above Class-1 levels of radiation, which cannot harm humans. A Blu-ray player is a good day-to-day example: it is a completely safe product that anyone can use, however it contains a Class-3 laser.
From Class-4 to Class-1
Therefore the simplest way for handheld laser welding systems to be made totally and unquestionably safe for the user, is to turn them into Class-1 laser products. However, is this even possible?
According to Tyrer, ‘yes’ is the simple answer to that question.
He made his point by first explaining that the fire and fume hazards that exist for handheld laser welding also exist for handheld laser cleaning – another application on the rise where the beam is often hitting the processing surface at an angle.
‘We've genuinely had companies come to us and say, “we have this opportunity to use this handheld laser welder or cleaner, but we're really conscientious because we have our operators working in big yards or on big building sites – is this safe?” and we’ve said “no, not at all” and they say, “but we’ve been told it’s safe” and I say “Go on then, I see you're processing stainless-steel, I'll give you 10 years before you start getting respiratory problems, skin issues, unknown bleeding in various parts of your body etc.”
‘And so we've been working with companies developing and using these systems and adjusting them so the beam hits the surface perpendicularly. That's better as it means the backscatter comes straight back up, and then you can put a guard over the whole process that collects the scattered radiation. These guards not only capture the backscatter, but also contain fume extraction technology, contact sensors, and backscatter sensors. If these sensors detect the guard moving away from the surface at all, or that the laser is no longer hitting the target, then it turns the laser off within a microsecond.’
Tyrer explained that such guards – which he emphasised can be developed for both handheld laser welding and cleaning equipment – are so effective that they transform a handheld laser device into a Class-1 laser product, meaning anyone can use it and observe the process safely without the need for goggles, masks, safety training, or any external fume extraction technology. ‘These guards are not only effective, but are also so much more affordable and convenient than laser safety enclosures,’ he remarked. ‘I believe that in time, as people recognise the risks associated with handheld laser materials processing systems, these guards will be sold with them as standard.’
When asked for images of such guards, Tyrer explained that a provider of handheld laser systems he’s worked with to develop them would not like them to be released, as they would like to maintain the competitive advantage that they believe they will have over their competitors once the system hits the market.
Until then however, if you decide to purchase a handheld laser welding system for your business, as highlighted by Lawton, you’ll need to perform numerous risk assessments, employ the necessary laser safety personnel, undertake any required safety training, purchase the essential safety equipment, and take all the additional precautions associated with wielding a Class-4 laser. More importantly, as highlighted by both experts, these systems must also be used in a way that does not expose the user to levels of radiation and hazardous materials that exceed the limits dictated by governmental regulations (unless you wish to risk incurring the wrath of the HSE that is!).
Share your experiences
Has your firm purchased and successfully used a handheld laser welding system? What have your experiences been and how did you ensure maximum user safety? Let us know at: firstname.lastname@example.org