Make no mistake, UV-C light is harmful to the skin and eyes and therefore suitable precautions should be taken to avoid any personal exposure.
Fixed mounted lamps should only be operated in unoccupied rooms and areas, with timers, sensors or interlocks fitted. Full personal protective equipment is required if the operator is present or if using a hand held lamp.
Our UV-C Hand Held Sanitiser can be used safely in occupied spaces on items and surfaces, but DO NOT point the lamp towards the body or any other person.
For organisation looking to implement the UV-C germicidal light sources into their premises by way of fixed mounted lamps or our UV-C Mobile Room Disinfection Trolley. There are legal requirements that needs to be met, such as a Risk Assessment / Health & Safety for staff and personals that would be operating the machines or present whilst in operation. Please contact us for further information on Risk Assessment, Health and Safety Training.
UV-C light exposure limits
Most UV-C light sources have a narrow spectral output at 254nm, for which the legal exposure level is 60 J/m2 within an 8-hour period. The maximum permissible exposure time at this wavelength can be calculated using the formula below.
UV-C dose (J/m2) = UV irradiance (W/m2) x time (seconds)
Therefore if we populate the dose (60 J/m2) and can accurately measure the UV-C irradiance, we can work out the maximum exposure time for the unprotected skin and eyes.
UV-C irradiance measurements are specific to a particular position, the irradiance level will be higher the closer you are to the source, and reduce with distance. Therefore it may be that multiple measurements need to be taken at different positions/distances to calculate different exposure times.
This can only be done if using a narrow spectrum 254nm source and a UV-C light meter with a peak spectral response at 254nm. It does not take in to account other wavelengths for which the exposure level will vary. As you can see in the table below, the higher the UV-C irradiance level, the shorter the exposure time will be.
Based on the exposure limits, the UV-C irradiance reading would need to be 0.002 W/m2 or lower to avoid exceeding the limits within an 8-hour period.
Maximum exposure times for the unprotected skin and eyes at 254nm
|Measured UV-C irradiance at 254nm||Maximum exposure time for the unprotected skin and eyes|
|< 0.002 W/m2||> 8 hours (exposure level cannot be exceeded in 8 hours)|
|0.01 W/m2||1 hour 40 minutes|
|0.02 W/m2||50 minutes|
|0.1 W/m2||10 minutes|
|0.2 W/m2||5 minutes|
|1 W/m2||1 minute|
|2 W/m2||30 seconds|
|10 W/m2||6 seconds|
|20 W/m2||3 seconds|
|> 60 W/m2||< 1 second|
Unfortunately most UV-C light meters are not sensitive enough for this, so professional help may be required. Most off the shelf UV-C irradiance meters measure from 1 W/m2 to 199 W/m2 which would give you a maximum exposure time range of 60 seconds to 0.3 seconds.
For instances where exposure is seconds (rather than minutes or hours), it’s best to eliminate any personal exposure rather than work within or up to the limits. It’s important the right units are used for these calculations to avoid errors in calculating the maximum exposure times.
There are some UV-C lamps that operate whilst people are in the room, referred to as upper air units. These lamps have louvres/baffles on which restrict the UV light to the top of the room (above head height), disinfecting the air as it naturally circulates around the room as it warms up and cools down. It’s essential that measurements are taken when installing these lamps to ensure there is no light reaching areas where people could be exposed.
Adverse health effects of overexposure to UV-C light
The after effects of overexposure to UV-C light are not always immediate, and often to not appear for several hours. They can vary in severity depending on the duration of exposure.
- Erythema (sun burn); reddening of the skin, rashes, peeling, etc;
- Photokeratitis (arc-eye); inflammation of the cornea and conjunctiva, results in a gritty feeling in the eye.
UV-C light risk assessment
We work closely with experts in the UV-C technology field, who can provide your company with Risk Assessment, Health and Safety Training to protect you, your staff and visitors to your premises. Please contact us for further information.