Safe Distances

By calculating the nominal hazard zone, laser operators can better understand their equipment’s safe zone


“Although laser light – power and radiation – is essentially the same as other forms of light, to which we are accustomed, it’s highly concentrated, travels in one direction and is coherent. These factors allow the laser to be formed and focused, which could potentially lead to a beam collecting in a person’s eye – a primary concern when working with industrial laser equipment.”

Those are the words of Thomas J. Lieb, CLSO and president of L-A-I International, an engineering, consulting and manufacturing company that creates safety and application solutions for some of the nation’s most demanding client needs. Lieb’s company has more than 25 years of experience with state-of-the-art laser cutting, welding, heat-treating, drilling and machining equipment – the type that has helped position the company as a go-to partner for aerospace, defense and power generation manufacturers. This type of equipment, however, requires the utmost safety standards to ensure that L-A-I International’s clients’ employees stay free from laser-related injuries.

“With sufficient power, [lasers] can cause burns and permanent blindness, beginning with Class 3B lasers,” Lieb says. “Material processing lasers – Class 4 – are an even higher hazard class and are most commonly invisible and infrared. Invisible infrared lasers have the double whammy in that you could be injured and never see it coming.”

Lieb goes on to describe the lasers that could potentially be the most hazardous to a person’s eyesight: near-infrared lasers, which include fiber lasers, YAG lasers and diode lasers. They are the most hazardous because they can be absorbed in the retina, similar to visible red light. If exposed to the longer wavelength CO2 laser radiation, a person could be subjected to skin and corneal burns and permanent blindness.

Point blank, Lieb says, “If you don’t like burns and you want to keep your eyesight, put a set of guards around the nominal laser hazard zone and stay out of it.”


The Evaluator from the LIA calculates the nominal hazard zone and also allows users to experiment with different types of eyewear, barrier combinations and laser power with graphic displays showing the outcomes of these combinations.

Staying out of harm’s way

No matter the size of an organization, safety is paramount when dealing with lasers with a Class 3B designation and higher. Once a company has identified its laser class designation, the next step is defining the nominal hazard zone (NHZ). When working with lasers, Lieb says that the “‘safe’ or ‘safer’ area is found outside of the defined NHZ.” Additional information about NHZ and maximum permissible exposure (MPE) can be found in ANSI Z136.1 Safe Use of Lasers, available from the Laser Institute of America.

According to a report from the University of Chicago’s Office of Radiation Safety, the NHZ is “a distance within which the irradiance of a beam is greater than the MPE. Besides being specific to a given wavelength and time of exposure, a different NHZ can be defined for the beam’s path to your eye – direct viewing, specular reflectance or diffuse reflectance.”

Although defining the NHZ seems complex in nature, it’s a practical definition, the report goes on to say. To explain, the report offers the example of a lab room that has no windows and a solid door. In this scenario, the NHZ would be the floor area of the lab itself. Inside the lab, people would need personal protective equipment, or PPE, usually in the form of laser attenuation eyewear of a specific optical density – calculated on the source laser wavelength and power. Outside the lab, people would be considered safe.

Just as the researchers at the University of Chicago must define the NHZ to ensure safety, so must laser operators in a manufacturing or fabricating environment. As was alluded to in its definition, calculating the NHZ is two-fold. One must first calculate the MPE before determining the NHZ – a fairly involved equation.

Luckily, most laser OEMs provide owners with the NHZ information, removing the need to do complex in-house calculations. However, there are some instances where the NHZ measurement from the OEM does not suffice.

“In some places, a single value suffices for a broad range of conditions,” the University of Chicago report explains. “In other cases, notably those of visible and near-infrared radiation during ordinary time periods of exposure, the MPE should be calculated on a case-by-case basis.”

To simplify the task, the LIA offers a tool called The Evaluator – a web-based NHZ calculator.


Whether it takes place in a classroom or online, thorough training is essential to ensure safety when working with lasers.

Calculations made easy

The Evaluator is a system that calculates the NHZ via an easy-to-navigate interface. This tool is particularly useful for an organization’s laser safety officer (LSO). An LSO – the individual responsible for implementing control measures to keep workers safe around lasers – should be appointed in any manufacturing environment with lasers in the Class 3 range and above. 

Based on ANSI Z136.1 Safe Use of Lasers, The Evaluator gives users the ability to determine the NHZ and to check their safety calculations for accuracy, quickly and easily. It could also be considered an educational tool as it allows users to experiment with different types of eyewear, barrier combinations and laser power with graphic displays showing the outcomes of these combinations. 

Anyone familiar with Software-as-a-Service will enjoy the fact that this solution also lives in the cloud. Rather than requiring a user to install software and manage updates, The Evaluator is accessed through the Internet — through which the vendor performs all maintenance and updates.

Users, however, have full control over settings, which means they can jump from continuous wave, single pulse or repetitive pulse lasers. Users can just as easily adjust the beam profile from rectangular, circular or elliptical.

To get a better idea of how the exposure will affect the human eye, the LIA tool provides a graphic that displays the eye and the varying effects exposure will have on the skin, retina or cornea. It’s designed with the LSO in mind, providing him or her with reports, graphs and a notes section where suggestions for improvements can be made.

Keeping up on the ANSI definitions and references to keywords and acronyms is no longer a hassle as the system includes an updated version of all of them.

Fortunate for big and small companies alike, the LIA is not offering this system as a one-size-fits-all solution. Organizations of any size can get access to The Evaluator through a subscription level that suits them best:

• A basic subscription offers the essential and fundamental laser hazard calculations in an easy-to-understand format.
• The intermediate level subscription, which is currently the most widely used, is a good fit for industrial applications and businesses where laser safety calculations are needed for prevention of hazards to the eyes and skin.
• Research facilities, the military, advanced laboratories and governmental organizations are fond of the advanced subscription, which includes features for performing the most sophisticated laser calculations.

Further options

In addition to The Evaluator, software packages are available from a number of different sources, such as Lazan software from Rockwell Laser Industries. Although the options are comparable, Rockwell’s tops the list for calculation accuracy. EasyHAZ software from Kentek Laser Store is also a viable choice.

“They all have a choice of complexity based on the user’s application, from basic to professional or expert,” says Lieb. “It’s important to understand, though, that even with software, a person should have the expertise to understand the parameters that go into the formula and also be able to do the calculations manually. This helps an organization avoid garbage-in, garbage-out results.”

For laser users who need to better understand the fundamentals behind manually calculating the NHZ, there are various options.

“At a bare minimum, every laser shop must have a copy of ANSI Z136.1 Safe Use of Lasers and any of the other numbered standards which pertain to their use, like ANSI Z136.9, Safe Use of Lasers in Manufacturing,” Lieb says. “The ANSI standards have examples and recommendations and even handy look-up tables, which may eliminate some of the calculations.”

He cautions that knowing the NHZ is not always enough. A comprehensive understanding of the equipment and the available safety measures is always the best line of defense. Therefore, the LIA offers a host of ways for laser owners and operators to receive training based on the ANSI standards appropriate for their needs. Be it in a classroom, online or an educator holding a course on-site, thorough training is essential.

“Many defined NHZs are too large and far away from the work to be practical,” he says. “In other words, if the NHZ were the only safety precaution, workers couldn’t get close enough to their machine to work. And, the NHZ is often demarked by an imaginary line in space, which is hard to get people to pay attention to. The best protection is to always implement some kind of guard, block or other device between the worker and the hazard.”

To truly embrace safety first, shop owners must take the appropriate steps to safeguard employees. It starts with designating an LSO, understanding a piece of equipment’s laser class, calculating the NHZ and implementing the right safety equipment. It continues with ongoing training and instilling a deep culture of safe and smart behaviors on the shop floor. For assistance at any step along the way, shop owners should always remember that the LIA is equipped and ready to help.

L-A-I International
Laser Institute of America

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