Safety Tips for Using Germicidal Lamps

What Are Germicidal Lamps?

Germicidal lamps emit radiation in the UV-C portion of the ultraviolet (UV) spectrum, which includes wavelengths between 100 and 280 nanometers (nm). The lamps are used in a variety of applications where disinfection is the primary concern, including air and water purification, food and beverage protection, and sterilization of sensitive tools such as medical instruments.

Germicidal light destroys the ability of bacteria, viruses, and other pathogens to multiply by deactivating their reproductive capabilities. The average bacteria may be killed in 10 seconds at a distance of 6 inches from the lamp. The wavelength with the greatest effectiveness is 253.7 nm, which defines the germicidal lamp category with optimized wavelength for maximum absorption by nucleic acids. Germicidal lamps that generate energy wavelengths shorter than 250 nm (particularly 185 nm) are very effective in producing ozone, which is required for certain applications to oxidize organic compounds.

Hazard and Risks from Germicidal Lamp UV Radiation

UV radiation (UVR) used in most germicidal bulbs is harmful to both skin and eyes, and germicidal bulbs should not be used in any fixture or application that was not designed specifically to prevent exposure to humans or animals.

UVR is not felt immediately; in fact, the user may not realize the danger until after the exposure has caused damage. Symptoms typically occur 4 to 24 hours after exposure.

The effects on skin are of two types: acute and chronic. Acute effects appear within a few hours of exposure, while chronic effects are long-lasting and cumulative and may not appear for years. An acute effect of UVR is redness of the skin called erythema (similar to sunburn). Chronic effects include accelerated skin aging and skin cancer.

UVR is absorbed in the outer layers of the eye – the cornea and conjunctiva. Acute overexposure leads to a painful temporary inflammation, mainly of the cornea, known as photokeratitis. Subsequent overexposure to the UV is unlikely because of the pain involved. Chronic exposure leads to an increased risk of certain types of ocular cataracts.

Working unprotected for even a few minutes can cause injury. It is possible to calculate the threshold for acute effects and to set exposure limits. It is not possible, however, to calculate threshold for chronic effects; therefore, because no exposure level is safe, exposure should be reduced as much as possible.

10 CFR 851 mandates the use of the threshold limit value (TLV) exposure limits established by the American Conference of Governmental Industrial Hygienists (ACGIH). The exposure limit for a germicidal lamp is 6 millijoules per square centimeter. At this level, detectable molecular damage appears to be fully repaired within 24 hours. For the case of continuous exposure for longer than 8 hours, such as is possible for a 10- to 12-hour extended shift or a double shift, special care needs to be taken.

Use of Germicidal Lamps

Biosafety cabinets

UV light has been used in the research laboratory as an effective germicide and virucide for most vegetative organisms and viruses. While it is used for disinfecting the interior surfaces of biosafety cabinets (BSCs) before and after use, UV does not penetrate well and will only disinfect the outer surface of any material stored in a BSC.

Administrative Controls

If interlocks are not fitted, the equipment must be used in conjunction with strict administrative rules to avoid exposure. Typical administrative controls include limiting access, ensuring that personnel are aware of the potential hazards, and providing training and safe working instructions for users.

Training

Personnel should be trained in using the UV equipment safely. The manufacturer’s manuals provide specific safety-related information (type of eye/skin protection needed, ventilation requirements, etc.) that must be completely understood before using the equipment. If any uncertainty or concern exists regarding the safe use of UV-generating equipment, contact the manufacturer for clarification.

Personnel should carefully study the manufacturer’s manuals of the UV-generating equipment and be familiar with its use. It is important never to deviate from the instructions for safe operation without first contacting the manufacturer.

At a minimum, lab personnel should be familiar with the following when working with or around UV light:

• Proper use of the UV light–producing equipment
• Warning signs and labels
• Proper use of protective equipment provided by the manufacturer (e.g., UV shields or enclosures), as well as PPE
• Symptoms of UV exposure

Minimizing exposure

• Never view the UV lamp directly. Although the inverse square law applies to non-laser-beam UVR, it is not advisable to look directly at any UV source (e.g., a germicidal lamp) at any distance.
• Keep exposure time to a minimum and keep as far away from the source as practicable.
• Turn off UV lights before working in the BSC.
• Restrict access to those personnel who are directly involved with the operation of the UV source. Do not loiter near the cabinets.

To continue reading this article and learn about the PPE required when using germicidal lamps as well as their limitations, click here.

Previously Featured on Lawrence Berkeley National Laboratory's site.