Ultraviolet light sterilization

Ultraviolet light sterilization Standard Operating Procedure

For survival surgical procedures, it is imperative that surgical components are sterilized so that they are free of bacteria, viruses, and other germs that could spread to the surgerized animal. Typically, autoclaving or anti-microbial solutions are used to sterilize surgical components. Sometimes, these standard methods cannot be used, either because the tools must be used in the field, or when the surgical tools or components are sufficiently delicate. In these cases, irradiation with ultraviolet electromagnetic radiation (UV light with a wavelength of approximately 254nm) can be very effective. Ultraviolet light, at sufficient energy, denatures DNA in small microbes and can be used as a sterilizer. This SOP describes how to use UV light to sterilize surgical tools and components.

A. Specific hazards:

  1. Prolonged exposure to ultraviolet light over time can increase the risk of skin cancer. For this reason, most ultraviolet lights for sterilization are enclosed with materials that block the ultraviolet light from the human operator. Do not override safety mechanisms that require the enclosure to be closed.

  2. UV radiation works best on smooth materials; some surgical tools, such as needle holders, that have rough, ridged surfaces, cannot be effectively sterilized by UV radiation.

B. Use in the lab:

    1. It has been shown that a radiation dose of 320mJ/cm2 is sufficient to kill common germs

    2. Before using an instrument that produces UV light, determine whether the device produces the proper wavelength (254nm) by reading the documentation or by measuring the light spectrum with a spectral radiometer

    3. Every quarter, calibrate the power of the light source with a power meter, such as Thor Labs PM100D with S121C sensory.

      1. Place an aperture of known size (say, 2mm) over the sensor, and measure the power produced by the light source at the same distance that the component will be placed. If the component is inside a case (such as a centrifuge tube), measure the power on both sides of the case (where the light shines upon it, and where the light passes through on the outside), and calculate the average of these two measurements. Your power measurement should have units of mW.

      2. Now, divide by the area of the aperture to obtain the irradiance in mW per cm 2 (if your aperture is 2mm, then use pi * 0.2 cm * 0.2 cm).

      3. Now that you have the irradiance of the light source at that distance, let's say IR mW/cm^2, calculate 320mJ/cm^2 / IR mW/cm^2 to obtain S, the number of seconds needed to provide a dose of 320mJ/cm^2. (mW/cm^2 * time = mJ/cm^2)

    4. Expose the component for the necessary duration to obtain a dose of 320mJ/cm^2. If the light source only comes from one side, turn the component and repeat the dose on the other side.

C. In the event of accidental human contact:

    1. A short accidental exposure should be have no health consequence.

D. References:

Walker RW, Markillie LM, Colotelo AH, Geist DR, Gay ME, Woodley CM, Eppard MB, Brown RS. Ultraviolet radiation as disinfection for fish surgical tools. Animal Biotelemetry 2013, 1:4