For most of us, flipping a wall switch is pretty much all we know about light. But, what we don’t know can hurt us – especially our eyes.
Both ultraviolet (UV) radiation and infrared (IR) radiation are potentially dangerous and exposure is common in many workplaces, so understanding what makes them dangerous and how can we reduce exposure is important.
This takes a bit to follow, but I promise it will be worthwhile knowing from an eye safety perspective. UV and IR radiation are part of the electromagnetic spectrum. The electromagnetic spectrum ranges from gamma rays at the high energy end to AM/FM radio and short waves at the low energy end. In the middle of this energy spectrum is visible light energy. Our eyes are designed to receive and interpret this electromagnetic energy in what we call visible light.
When we are exposed to excessive visible light we are protected by automatic pupil dilation to reduce the energy entering the eye. If the levels of visible light are very high, we can detect this quickly and instinctively close our eyes or turn away from the light source.
The problem is UV and IR radiation are invisible to the eye and exposure is not detectable, although IR radiation may be felt as heat. UV exposure is particularly high for workers involved in welding, brazing, and cutting operations. IR radiation is also common in these and similar operations, as well as in work around furnaces and molten metal production. Exposure to UV and IR radiation can occur in numerous workplace environments such as: outdoor work, steel mills, textile production, glass production, manufacturing, maintenance, and in industries where lasers, arc lamps, furnaces, or where electric radiant heaters are used.
Exposure to one or both is potentially damaging to the eyes, because unlike visible light our eyes are not calibrated to measure the intensity and our pupils will not respond and contract to protect us from excessive exposure. Without this natural defence, exposure is particularly dangerous to the eyes. And, even when we are being exposed to UV or IR radiation significant enough to cause damage, our sensory perception will not indicate the exposure is damaging.
Damage associated with UV and IR radiation exposure is usually chronic, occurring slowly over time. Both can cause cataracts, or a clouding of the lens, which can lead to vision loss. The more concentrated the source of exposure, the more potentially damaging it is to the eye. For this reason, employers must recognize the exposure potential, assess the hazards, and ensure proper controls are in place. Conducting an assessment will determine the level of exposure and appropriate protective eyewear can be selected. Sources of exposure should also be identified as part of the hazard assessment process. A program including engineering, administrative and personal protective equipment are typically employed to minimize the source of radiation wherever possible. The most common part of the control strategy is the use of safety eyewear. Selecting the correct safety eyewear to protect against UV and IR is specific depending on the source and wavelength of radiation and the duration of work activities.
The requirements for protecting the eyes against UV and IR radiation are provided in Canadian Standards Association (CSA) Standard Z94.3 Eye and Face Protectors. CSA Class 1-4 safety eyewear fitted with an appropriate lens will provide protection from UV or IR radiation where a moderate or large amount of shielding is required. The Standard allows for the use of spectacles, goggles, welding helmets, or welding hand shields fitted with the appropriate lens. UV protection can be achieved by a specific treatment or colouring of safety eyewear lens. Some polycarbonate lenses have UV protection inherent in the materials of construction. IR protection is achieved by specific colouring of the lens. UV and IR protective safety eyewear come in a variety of shade levels (specified in the CSA Standard) ranging from 1.5 to 14 appropriate for the intensity of radiation. Table A.1 of the Canadian Standards Association Standard Z94.3 Eye and Face Protectors lists the range of options when selecting safety eyewear for UV and IR protection.
Users should be aware clear and tinted lenses that provide protection against UV radiation cannot be used interchangeably to protect against IR radiation. Only shaded lenses designed and approved for the specified type and level of radiation may be used.
When selecting protective eyewear, ensure it is approved for the specific use in which it will be employed, based on density of the wavelengths present in each workplace scenario. It is also important to remember that welding helmets and welding hand shields, although protective against UV exposure, are not primary eye protection approved for the workplace. Safety glasses should always be worn underneath to protect the eyes from other hazards when the helmet or hand shield is lifted. Your Eyesafe plan offers a wide selection of safety glasses to fit every face, and also provides safety lens inserts for masks.
Exposure control is essential to the effective and long-term protection of workers, and controlling exposure is manageable with proper planning and selection and use of safety eyewear.
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.