High Power Laser Safety

Laser safety is a commonly misunderstood topic. Here are several of the major hazards of industrial class 4 lasers, and the current methods of protection.

• By Spencer Lane
• Mar 26, 2020

In my time as a Laser Safety Officer for the US Navy, I advised on the safe use of several industrial lasers for long established processes as well as experimental use including metal cutting, engraving and surface ablation. In this time, I found that despite the fact lasers have been around for decades, the published knowledge of laser safety is shamefully lacking, even among experts in research and industry. Much of the information about the hazards associated with lasers has thus far been left as inadequate or incomplete knowledge.

To help with understanding the hazards associated with high powered lasers, listed below are several of the major hazards of industrial class 4 lasers, and the current methods of protection. Also, to clarify, while class 4 lasers are defined as being above 500 mW power output, there are many lasers in industry and research capable of power outputs in the kW range or higher, referred to as “high powered lasers” (1 kW = 1,000,000 mW).

Burns and Blindness:

The obvious hazard with lasers is the possibility of blindness. Even if the laser in use has a wavelength outside of the eye's sensitivity range (400-1400nm, visible and near infrared light), damage to the eye can still occur. While direct blindness from the laser light is no longer a concern outside of the sensitive range, there are still many other ways the eye can be injured by energy from laser light. Burning of the eye, distortions of the eye’s shape reducing vision, boiling of the eye’s fluids, denaturation (decaying) of the proteins in the eye causing milky white blind spots, and internal bleeding are all still possible symptoms of laser light directly input to the eye. Also, just because the beam is not visible light (400-700nm) nor near infrared (700-1400nm), does not prevent instantaneous damage and blinding. If the laser’s energy output is high enough, instant burn damage is still possible, much like touching a hot stove top.

Direct exposure to the laser is the most dangerous scenario, but not the only hazard. Additionally, to direct exposure to laser light, indirect exposure from reflected beams can also be hazardous depending on the circumstance. There are two types of reflection: specular (the beam reflecting off of a smooth surface or partially reflecting off of or through glass where a beam continues on its new path) and diffuse (the light scattering in all directions off of a rough surface like the light from a light bulb spreading out). When a beam is reflected, some energy is partially dispersed, but if the laser has enough initial energy, the reflected beam can still be dangerous.

Because reflected beams are still coherent lasers, they should be treated the same as a beam directly from the laser’s source. Diffuse laser light is typically dispersed enough to be harmless, but the diffuse light from a class 4 laser has enough energy to be harsh on the eyes, degrading sight over time without proper eye protection.

The best practice for controlling laser beams from affecting people not involved in the process is to only position and use lasers in an enclosed room. If possible, a completely enclosed workspace with ventilation is best (such as a repurposed painting booth).

Chemical Hazards (welding-like hazards requiring hotwork safety practices):

Many industrial lasers are used for cutting, etching and ablating (like sanding or grinding) where they are burning away material, making high powered lasers hazardous in the same way as many hotwork jobs such as welding. Due to the principle of conservation of mass, the materials burned away do not disappear into oblivion and nothingness. Instead, these materials are combusted, and they exist as toxic gasses in the air. Toxic offgas forms from lasers burning metals and other solid materials, as well as oils, solvents, and other chemicals which can burn off into the air or evaporate into the air when exposed to the concentrated energy of lasers.

To protect against inhaling these toxic gasses, hotwork style laser work needs ventilation. While air circulation throughout the area where the work is being done helps, such methods only dilute the offgas. Local exhaust ventilation where a suction tube is placed immediately next to the laser work to vacuum up the gasses is the best way to effectively control the creation of offgas in significant quantities.

Hazardous Energy (other than light):

High powered lasers have a lot of electricity flowing through their internal mechanisms (as the name would imply). Because of this, all covers need to be in place to prevent electric shock from a live wire or other electrical contact. Furthermore, due to the capacity for injury or death when working with such machines, Lock Out Tag Out [LOTO] procedures are important to have implemented and followed when performing maintenance. While electrical safety and LOTO are far too large of subjects to cover here in depth, they should be kept in mind for working with high powered lasers.

Destruction of Personal Protective Equipment [PPE]:

Laser safety glasses, when properly selected, can prevent or significantly reduce laser injury. However, when laser power output reaches the kW level or higher (especially for some low-quality laser safety glasses), the amount of energy from the laser can melt the safety glasses. Because of this, when working with high powered lasers, it is important to consider the setup of the laser to mitigate the risk of direct exposure to the beam. PPE is important for keeping safe, but with high powered lasers, safety gear can provide a false sense of security. When working with these high-powered lasers, safety equipment can NOT guarantee protection.

Hierarchy of Controls:

When considering how to protect against laser injuries, consider the hierarchy of controls, used to focus attention on the safest solutions first.

• Eliminate. Can the process be done without the use of a laser? With a less powerful laser? Will an alternate process be more or less hazardous than using a laser? This can be difficult to judge without a strong risk assessment tool as alternate processes will often have different types of hazards.
• Isolate. Can the laser be used in a way so that no personnel can possibly be exposed to the laser's high energy light (ex: in a sealed room using an automated process or remote control via camera feed with interlocks on the doors to shut down the laser if anyone enters)?
• Engineering controls. Can interlocks, barriers, or other physical controls prevent dangerous levels of laser light from reaching the workers, laser users and passerby? Such physical methods of control are useful as they are effective even when a worker becomes distracted.
• Administrative controls. What best practices can be implemented (such as enforcing distance or work location) to prevent injury? Administrative controls are weak safety additions, as they require attention and compliance to be effective. Deliberate disobedience or a momentary lapse of thought can undermine the safety provided by administrative controls.
• PPE. Can the use of safety equipment such as laser safety glasses reduce injury. Safety gear is the least effective as it does not prevent injury—only reduce the effects. Further, as discussed above, laser safety glasses can be melted by the extreme level of energy output by some high power lasers rendering the PPE ineffective.

Ignorance Compounded by Poorly Written Instructions:

Unfortunately, laser safety is a poorly understood subject in industry. The great danger is ignorance compounded by a lack of information. Without understanding, the many and diverse dangers presented by high powered lasers, laser users and workers will continue to be at risk of injury, often without knowing the danger they are in.