While safety glasses need to be worn to provide protection, lens fogging can also create a significant safety issue. If you take the glasses off to clear the fog you can be creating a safety hazard and possibly a compliance issue. For construction workers, welders, first responders, and many other workers, dealing with fogged eyewear can be both dangerous and incredibly frustrating. During winter months when the outdoors is coldest, fogged safety glasses become a problem for all workers, but especially so for workers that constantly go in and out from heated buildings to the cold outdoors.
So why do safety glasses fog? It’s simple physical chemistry. When outside in the winter cold the lenses quickly cool to be close to the outside temperature. When you go back inside, the cold surface of the lens allows the moisture that is in the inside air to condense on the lens. This condensation happens because the safety glass lens is colder than the dew-point of the warm moist inside air. After a few minutes, the lens warms up to the inside temperature and the fog that formed evaporates clearing the lens.
The main contributing factors to your fogging safety glasses in winter include:
- The difference between indoor and outdoor air temperatures. The bigger the difference the faster the lens will cool.
- The amount of time spent outdoors. The longer spent outdoors ensures the lens will completely chill.
- Indoor humidity. The higher the indoor humidity the greater the fogging.
- Cleanliness of the lens. A dirty lens will fog faster and more completely.
- The age of the lens. An older and scratched lens will fog faster and more completely.
- Human exertion. Working hard increases the humidity in the air between the lens and your face.
Skiers, swimmers and skin-divers have used an age-old solution to reduce fogging – spitting on the lens. Although not the most hygienic solution, understanding why it works helps to understand the science of fogging. Spitting in your safety glasses reduces fogging because it creates a thin layer of saliva on the lens that prevents the first condensation molecules from forming. Condensation occurs at tiny little sites such as where dirt is attached or along the edge of a scratch on the surface of the lens. Spitting on the lens coats these sites preventing or reducing condensation.
There are better solutions available to prevent fogging, but there is no perfect solution.
Here are three strategies worth considering:
- Keep your safety glasses clean. Dirt and scratches create condensation sites that increase fogging.
- Use an anti-fog spray. The spray helps to clean the surface and acts to fill in or block the condensation sites, reducing fogging. For best effect always follow the manufacturer’s instructions for use.
- Buy safety glasses with an anti-fog coating. These anti-fog coatings act in a similar way to sprays, but in a more permanent way by preventing the development of micro-scratches that act as condensation sites. Anti-fog coatings work best when fogging is due to perspiration condensing on the inside of the safety glass lens. This is a different phenomenon and is usually a summertime problem.
If safety glass fogging remains an issue, stop when transitioning from outside to the inside to give your safety glasses time to warm up and lose the fog before proceeding with work. Don’t fall victim to incident and injury due to wintertime fogging of safety eyewear. Remember the cause of fogging and consider the necessary steps to eliminate it or prevent it from causing an incident.
Glyn Jones is a partner at EHS Partnerships Ltd. in Calgary. He is a consulting occupational health and safety professional with 30 years of experience. He is a regular safety conference speaker in Canada and he provides program design and instructional support to the University of New Brunswick’s OHS certificate and diploma programs.