Skip to main content

The Science of Fit

Why is fit so important when it comes to safety glasses?

When it comes to choosing the right safety glasses to help protect your workers’ eyesight, the most important thing to consider is the type of hazard they will be exposed to. Once you have determined this, the following three factors that should come into consideration are

  • Comfort
  • Fit
  • Security

Although fit and security are objective measures, comfort is harder to define since we know that comfort can mean different things to different people. If you read our article on how comfort can affect compliance, you’ll remember that when workers wear personal protective equipment (PPE) that is comfortable and fits properly, they’re more likely to stay protected from workplace injuries.

Why comfort and fit are related

When a pair of safety glasses fit well, they tend to feel comfortable to the wearer. Research has shown us that the number one aspect of comfort is actually related to the fit of the eyewear in terms of pressure on the temple above and behind the ears.[1] Head widths can vary significantly, which means that what feels comfortable for one worker might not feel comfortable for another. In addition to this, eyewear that feels comfortable on a larger head might not even be secure on a smaller head. This can make it hard to find one style of eyewear that fits comfortably on all of your workers.

The science of comfort

3M studied the differences in face shapes and sizes throughout the world. Digital models detailing approximately 600 different touch points on the human face aided in the design of the innovative 3M™ Brand Pressure Diffusion Temple Technology (PDT). PDT helps diffuse pressure over workers’ ears to enhance frame comfort across a diverse workforce without compromising the security of fit.

Science applied to eyewear fit testing

3M used the same 600 touchpoints on the face to develop the  Eyewear Fit Testing System to help evaluate the fit that a pair of safety glasses provides each worker.

Proper-fitting eyewear should be based on the view, security, coverage and gaps that a pair of safety glasses provides a worker.

  • View should not be obstructed
  • Eyewear should have security to remain on the face
  • There is sufficient coverage to ensure eyes and soft tissue around them are protected
  • No gaps should allow particles to come into contact with the eye

The Eyewear Fit Testing System evaluates the above components. The system should be used to test workers who already wear safety glasses to ensure they fit properly, as well as workers who are new to the facility. The fit test system should also be used every time new eyewear is brought in to make sure it fits properly . According to the CSA Z94.3.1 Guideline for selection, use and care of eye and face protectors, eyewear should be assessed every two years or whenever changes occur to a wearer’s physical condition (e.g. significant weight change or changes to facial features). Fitting of eye protectors should be completed for each model that the end user might wear.

The 3M™ Eyewear Fit Testing System is simple to use and employs two handheld measurement gauges to conduct the test. The safety glasses must be on the face and the middle line on the measurement gauge must be aligned with the middle of the wearers’ pupil. The goal is to ensure the eyewear meets or exceeds the coverage marks in both horizontally and vertically on the measurement gauges. The measurement gauge also evaluates six points across the top and bottom of the lenses. A gap less than 8 mm is preferred, with a gap less than 6 mm considered optimal. Gaps in the 10 to 12 mm range or larger should be carefully considered in the context of the working environment; gaps in the 6 to 8 mm range might be more suitable.

To learn more about the science of fit, visit or contact a 3M Safety Specialist  to request a demo of the 3M™ Eyewear Fit Testing System.

[1] David A. Lombardia, Santosh K. Vermaa, b, Melanye J. Brennana, Melissa J. Perry. “Factors influencing worker use of personal protective eyewear.” Accident Analysis & Prevention volume 41, issue 4, July 2009, pages 755-762.