Laser safety: laser classes, safety glasses and fire protection

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A laser engraver concentrates enough energy to vaporise wood. That same energy can damage your eye in a fraction of a second and can start a fire. This article explains what the laser class says about your machine, which safety glasses are suitable and how to prevent fires.

Laser classes according to DIN EN 60825-1

The standard DIN EN 60825-1 sorts laser devices into classes by how dangerous they are. For engravers, only two classes are relevant in practice: Class 1 and Class 4.

A diode laser with 10 W, 20 W or 40 W of optical power is far above the limit of 500 mW. Every open machine with such a source is therefore Class 4, which means practically every open diode laser, for example the Acmer P2 33W.

Class 1 does not mean that the machine contains a weak laser. It means that the housing reliably shields the radiation. Enclosed machines such as the xTool S1 20W or the Creality Falcon2 Pro 22W reach Class 1 through a tinted viewing window and a lid interlock.

There are two caveats you should know about:

• Class 1 only applies in the original condition. If you fit a riser underneath the machine without shielding, bypass the lid switch or replace the viewing window, it is a Class 4 device again. With the S1, xTool explicitly points out that Class 1 no longer applies with the Class 4 riser base.
• The classification has to come from the manufacturer. For some enclosed machines the manufacturer does not state a class. In that case, assume Class 4.

Safety glasses: wavelength and optical density

With any Class 4 machine you wear laser safety glasses, and so does everyone else in the room. Sunglasses or tinted workshop glasses do not protect you.

Two values are decisive:

Wavelength. The glasses must cover exactly the wavelength of your laser. Blue diode lasers usually work at around 450 nm (often stated as 445 nm or 455 nm), infrared and fibre lasers at 1064 nm, CO₂ lasers at 10,600 nm. Glasses for 1064 nm do not protect against a blue diode laser, and vice versa. For combination machines with a diode and an infrared module, you need glasses that cover both ranges.

Optical density (OD). The OD tells you how strongly the filter attenuates the light. Each step means a factor of 10: OD 5 still lets through one hundred-thousandth, OD 6 one millionth. For hobby diode lasers, glasses with OD 5 or higher at the matching wavelength are available.

In Europe, the standard EN 207 applies to laser safety glasses. Certified glasses carry a marking such as “D 445 LB5”: D for continuous wave, the wavelength in nm, and the protection level LB. LB5 corresponds to a transmission of no more than 0.001 per cent, so roughly OD 5, and also takes into account how long the filter withstands a direct hit. Glasses to EN 208 are alignment glasses and are not suitable for engravers.

When buying, look for:

• wavelength and protection level printed directly on the frame or lens
• the standard EN 207 stated, not just “OD 6+” without a wavelength
• side protection, so that no reflections reach the eye from the side
• the greenish glasses supplied with many open machines: only use them if the marking matches the machine

Reflections

With Class 4, it is not only the direct beam that is dangerous. Mirrored reflections and even diffusely scattered light can also damage the eye. The beam does not have to hit your eye directly. Reflective surfaces are particularly critical:

• bare metals such as aluminium, brass or stainless steel
• glass, mirrors and glossy tiles
• tools, rulers or jewellery near the work area

Take off your watch and rings when working at an open machine. Test new, shiny materials at low power first. And never look at the laser dot “just briefly” without glasses.

Fire protection

Small flames constantly appear when laser engraving, especially when cutting. Normally they go out immediately. If they do not, the workpiece can catch fire within seconds, and the machine shortly after.

Never leave it unattended. Stay within sight and within reach of the emergency stop for the whole job. Trotec also stresses that even industrial machines with fire detection should only run under supervision, and that insurers do not always pay out when a machine was running unattended.

Keep a fire extinguisher within reach. A CO₂ extinguisher is well suited to laser machines because it leaves no residue and is approved for electrical equipment. Powder extinguishers also work, but ruin electronics and optics. Place the extinguisher so that you can reach it without reaching past the machine.

Fire blanket. For small fires on the workpiece, a fire blanket is often enough. Stop the laser first, then lay the blanket over it.

Further rules:

• Use air assist, especially when cutting. It blows flames out.
• Regularly clear resin, ash and residue from the honeycomb bed and the bottom of the machine. These deposits burn easily.
• Do not store any flammable material under or next to the machine.
• A smoke detector in the room.
• Place the machine on a non-flammable surface, such as a metal plate or tile.
• Some materials are not only toxic but also particularly flammable. More on this under forbidden materials.

Children and pets

An open Class 4 laser does not belong in rooms that children or pets can enter unnoticed. Children look curiously at the bright dot, and animals’ eyes are just as sensitive as ours. Pets are also sensitive to the smoke.

In practice, that means:

• lock the room while laser engraving or keep the door closed
• a warning sign on the door if others live in the household
• have glasses ready for everyone present, including onlookers
• disconnect the machine from power after work so that nobody starts it by accident

An enclosed Class 1 machine is much less critical in living spaces. The fire risk and the smoke remain there too, though.

Class 4 lasers in a workshop or business: regulations

As soon as someone is employed by you and works with the laser or is in the same room, it is no longer just common sense but occupational health and safety law that applies. The most important rules at a glance, not to be taken as legal advice:

Private or commercial. According to § 1, the Ordinance on Occupational Health and Safety concerning Artificial Optical Radiation (OStrV) applies to the protection of employees at work. Under § 2 Arbeitsschutzgesetz (Occupational Safety and Health Act), employees include workers, trainees and civil servants, among others. If you laser privately at home, it does not apply to you. If you run a business and operate the laser alone, you have no employees within the meaning of the law either. But as soon as employees, temporary staff or trainees are added, you are an employer and must comply with the OStrV. For clubs, makerspaces and schools, the classification depends on who is employed there; if in doubt, ask the responsible Berufsgenossenschaft (employers’ liability insurance association) or Unfallkasse (public accident insurer).

Risk assessment. Under § 3 OStrV, the employer must check whether laser radiation can occur at the workplace and assess the hazards. The necessary information may be obtained from the manufacturer. Protective measures in line with the state of the art follow from the result. Under § 5 para. 1 OStrV, only competent persons may carry out the assessment.

Laser safety officer. Before operating laser equipment of Classes 3R, 3B and 4, the employer must appoint a laser safety officer in writing under § 5 para. 2 OStrV, unless they have the necessary expertise themselves. The qualification is proven by a course and kept up to date through further training. The laser safety officer supports the risk assessment, the protective measures and the monitoring of safe operation. For an enclosed Class 1 machine in its original condition, the ordinance does not require a laser safety officer; for an open diode laser of 10 W or more, it does.

Protective measures. Under § 7 OStrV, technical measures such as shielding and interlocks take priority over organisational measures, with safety glasses coming only after that. Areas where the limit values may be exceeded must be marked and demarcated, and access for unauthorised persons must be restricted. In addition, under § 8 OStrV, employees must be instructed before they start work and at least once a year after that.

TROS Laserstrahlung. How the OStrV is implemented in practice is described by the Technical Rules for the Ordinance on Occupational Health and Safety concerning Artificial Optical Radiation (TROS Laserstrahlung) of the BAuA. They consist of a “General” part (including requirements for laser safety officers and their courses) and three parts on hazard assessment, on measurements and calculations and on protective measures.

DGUV regulations. Laser safety officers existed long before the OStrV: according to DGUV Grundsatz 303-005, they had to be appointed since 1974 under the accident prevention regulation DGUV Vorschrift 11 “Laserstrahlung” (formerly BGV B2) or DGUV Vorschrift 12 (formerly GUV-V B2), and since 2010 the OStrV has required it. According to this Grundsatz, anyone who was trained only under the old regulations should have updated their training to the OStrV and TROS by the end of 2021. According to DGUV Information 203-036 (January 2021), DGUV Vorschriften 11 and 12 were still valid at some accident insurance bodies. Your Berufsgenossenschaft can tell you which accident prevention regulations apply to your business. The Institute for Occupational Safety and Health of the DGUV has compiled an overview of the regulations, rules and DGUV Informationen on laser radiation, for example DGUV Information 203-042 on choosing laser safety glasses.

Do not forget the smoke

Besides radiation and fire, smoke is the third risk. It contains fine dust and, depending on the material, toxic gases. How to get rid of it safely is explained in the article on fume extraction.

Continue with: Fume extraction for laser engraving and Forbidden materials.

What to consider specifically in a flat, from exhaust air to the tenancy agreement, is covered in Laser in a flat.