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Modern challenges in laser safety

‘Almost everyone looking to use lasers for materials processing should be looking to use a Class 1 laser product.’ 

Such began David Lawton of Lasermet (now Kentek, see bottom of page) as he sat down with me to talk ‘the latest in laser safety’.

The statement raised a number of questions, as despite being the editor of an industrial laser magazine, embarrassingly I was not fully up to scratch with my laser safety terminology. 

This is why I stopped Lawton immediately and let my curiosity get the better of me: ‘What does that term actually mean David: “Class 1 laser product”?’

While writing for Laser Systems Europe has taught me that you won’t find a materials processing laser lower than Class 4, I’d never actually stopped to think about what each class defines exactly.

Lawton was more than happy to indulge me, however.

‘The four classes of lasers have been determined based on each one’s ability to cause harm to the human body. 

Class 1 lasers are totally and unconditionally safe, there is no way they can cause human harm – think of a barcode scanner in a supermarket;  

‘Class 2 lasers are visible lasers that, while being able to cause damage to the eyes, take longer than a quarter of a second to do this – in which time your body’s natural reflexes will either close your eyelids or move your head out of the way of the beam before any damage can be done;

‘Class 3 lasers can be of both visible and invisible wavelengths and the beam or (specular) reflected beam can damage the eye or skin quicker than a quarter of a second. The diffused or scattered radiation of a Class 3 laser, however, is safe, as it does not pass the eye/skin damage threshold. In other words, they are only dangerous if you are in direct contact with the beam, looking at the spot itself will not cause harm.

Class 4 lasers however are able to cause damage with their reflected or scattered radiation – you can’t even look at the spot. This of course depends on the wavelength and power of the laser, divergence of the beam etc, but it could be dangerous.’

I was slightly alarmed when he explained that the power level of Class 4 lasers, rather than starting at hundreds or even thousands of watts, begins at no more than half a single watt. In case, like me, you need it pointing out, that means that while Classes 1, 2 and 3 cover anything up to 499mW, technically, a 500mW laser and a 100kW laser can belong in the same class when it comes to their ability to harm a human.

‘I feel like there should be at least a fifth class in there somewhere David.’

‘You’d be right in thinking that,’ he said, ‘and the potential creation of Class 5 is something that is being discussed, however where could the line be drawn for this? There’s an argument that suggests that: “if no PPE exists that can protect you from this laser, then that should be Class 5”, however for the moment, the general consensus is that everything that could do that is still in Class 4.’

With the class system covered, that brought Lawton to the second half of the term I queried: ‘laser product’. 

‘During normal operation, a Class 1 laser product will never expose the user to anything above Class 1 levels of radiation,’ he explained. ‘A great example is a Blu-ray player. This is a completely safe product that anyone can use without safety training, a risk assessment, signs outside the door etc. However it contains a Class 3 laser, meaning as soon as you open it up, you put yourself at risk.’

An interesting example, I thought, but how does this come into play in industrial materials processing?

This is where Lawton introduced his and Lasermet’s quite elegantly simple mantra: ‘put it in a box’.

Behind closed doors

The ‘put it in a box’ school of laser safety – as Lawton said it is colloquially known – is about creating an environment where no harmful radiation can escape and where no human can enter while a laser is active.

‘Why should you have to wear PPE if you can simply contain a laser in a controlled environment? Even the UK’s Health and Safety Executive (HSE) is starting to get in line with this way of thinking, advising people to “enclose laser radiation where possible”.’ 

This is in no way a new line of thinking. As in materials processing, there are very few lasers with which you can even stand in the same room. As a result, nearly all materials processing lasers are either contained in a laser machine, or instead have an enclosure erected around them, armed to the teeth with interlocked doors, active guarding, safety windows and bright LED signage.

‘Laser safety is about understanding the hazards, containing those hazards and making sure that nobody is exposed to them,’ continued Lawton. ‘This is why the “put it in a box” methodology is so elegant, because with it, laser safety isn’t actually that difficult. It can apply to anything from a small multi-watt laser on a tabletop, through to a turnkey system containing a kilowatt laser, and even on to, for example, a colossal enclosure that can take a part as large as an aircraft wing and process it using a multi-kilowatt laser.’

A laser enclosure in use live at a trade show thanks to its Class-1 laser product status. (Credit: Lasermet)

In this example, according to Lawton, the interlock-equipped enclosure could be made to have the same Class 1 laser product status as the aforementioned Blu-ray player.

‘The enclosure would have to be tens of metres in length, depth and height to contain such a process of course, but it could be done,’ he confirmed.

What Lawton said next enabled me to openly admit my lack of laser safety knowledge at the start of this article. I’d previously been under the impression that everyone involved in laser materials processing – besides myself of course – was well-versed in laser classes and what exactly a ‘Class 1 laser product’ was. This apparently isn’t the case, however.

‘So many times we’ve had to go to customers because they’ve bought a Class 4 laser when they should have just purchased a Class 1 laser product,’ he revealed. ‘For example one customer bought a Class 4 laser to mark parts on a production line. The manufacturer of the laser was under no obligation to tell the customer “by the way, because you now have a Class 4 laser in your organisation, you’ll have to perform a risk assessment, appoint a laser safety officer and provide additional training for your users.” If that customer had been savvy and instead just purchased a Class 1 laser product, they wouldn’t have had to do any of that in the first place.

Remote welding creates new challenges

While ‘put it in a box’ does somewhat simplify laser safety from a user perspective, the same cannot be said for those actually making the ‘box’.

Before I continue, those reading should first know that the cost-per-watt of lasers has dropped dramatically in the past 15 years.

‘Even within this decade lasers have been seen as a monster investment,’ said Lawton. ‘For example, one of our customers bought a 10kW laser a while ago for a whopping £1m. They’ve since bought a 30kW laser for less than that.’

Combined with the advent of fibre laser technology, this lowering cost has enabled lasers to be used increasingly for remote welding. ‘Previously, when CO2 lasers were the standard, welds would be performed at a 50 to 100mm standoff from the workpiece, using a system of mirrors to deliver the beam,’ said Lawton. ‘Fibre lasers enable the beam to be sent along an optical fibre and down a robotic arm, which combined with developments in optics enables remote welding to be performed up to distances of well over a metre. I have seen a laser 1.8m away from the focal point in such an application!’ 

A large laser welding enclosure in use at the Manufacturing Technology Centre in the UK. (Image: Cyan-Tec)

For that setup, Lawton explained, it would mean that even 1.8m past the focal point of the laser, the power density could be the same as it was when it originally came out of the optics – spread over a diameter of approximately 20mm.

The power density is still dangerously high away from the focal point, which from a safety perspective brings a whole new level of risk,’ he remarked. ‘Remote welding is a real challenge. While the whole process can still be put in a “box”, you have to determine whether the box is good enough to stop the beam. This will determine what sort of enclosure is required and what that enclosure will be made of.’

In testing enclosures, Lasermet has to fire lasers of different powers and spot sizes at its guarding to determine how quickly they burn through it. A protective exposure limit (PEL) rating is then given to the product. ‘You can then calculate the foreseeable exposure limit (FEL) on the guard, so we know how the laser will interact with it,’ Lawton explained. ‘As long as the FEL is below the PEL for the time required, then the guard will stop the beam, otherwise, the beam will burn through.’

Inside the MTC laser welding enclosure. (Image: Cyan-Tec)

In addition to accounting for various beam divergences and their intensities when building an enclosure for remote welding, Lasermet also has to consider what happens if the laser spot is reflected directly during processing, which is known to happen, according to Lawton: ‘Welding metal creates a molten pool that, due to surface tension, can sometimes act as a perfect reflector and bounce a powerful spot of radiation onto a guard, screen or wall.’

As a result, the firm has to presume the worst when building a laser safety enclosure: what happens if the laser gets locked in position, striking a wall directly at maximum intensity?

Children running the sweet shop

Thanks to the ‘worst case scenario’ measures taken by system and enclosure manufacturers, despite the dangers that lasers pose, owners of Class 1 laser products can have peace of mind that their laser is locked away safely behind closed, interlocked doors... right?

Not necessarily, as I soon found out thanks to Lawton’s final and rather shocking point: that anyone can self-certify a Class 1 laser product, and that most companies do just that.

This baffled me. To know that rather than being regulated and controlled by a governing body, the certification of a system containing a Class-4, multi-kW laser as a ‘Class 1 laser product’, has most likely been done by the system’s manufacturer. 

It’s quite common for manufacturers to self-certify,’ said Lawton candidly. ‘Even the largest and most respectable laser firms do this...“children running the sweet shop”, I call it!’

He quickly gave evidence to show that this remark was not unwarranted: ‘I have seen a UK company buy a laser product from a US firm, and the sources that the US manufacturer said were inside the device were not the sources in the delivered product. What had happened was that the US manufacturer had changed the sources a few years prior and not actually changed the product’s classification. This device went from being an eye-safe product to a non-eyesafe product, and had been sold worldwide.’

Asking Lawton why there hasn’t been any move towards legislatively controlling laser product certification, he said that such a question had indeed been raised before at an annual laser safety forum in which he takes part. ‘The argument that came back was that there are many other aspects of products, for example regarding electromagnetic compliance, the low voltage directive etc, that are listed in a declaration of conformity – almost all of which can be self-certified.’ 

Seeing that I wasn’t convinced that such an argument was strong enough to justify a lack of legislative control over laser certification, Lawton asked rhetorically: ‘Is it right that a manufacturer can say ‘this is a “Class X” laser product, and you’ll just have to take my word for it?

While Lasermet was accredited by the UK’s National Accreditation Body (UKAS) in July, which enables it to test the safety of customer’s laser equipment in-situ to the laser safety standards BS EN 60825-1:2014, 2007, 2001, such independent tests are not yet compulsory by law.

I’d like to think that this could one day change. However, if any of you out there can convince me otherwise as to why this would not be a good idea, feel free to voice your thoughts in an op-ed for our next issue:

At the time of writing, David Lawton was European sales manager at Lasermet, he has since moved over to US laser safety equipment manufacturer Kentek, where he now works as the European market development manager.

Read more about:

Safety, Aerospace, Fibre lasers, Welding

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