Bulletin 77

Bulletin 77

Surface Disinfection

Surface disinfection usually requires high intensity UVC radiation.  The design and placement of lamp fixtures dictates mounting UVC lamps in a relatively close proximity to the surface being irradiated to achieve disinfection goals.

 This applies to surface or granular material being irradiated and by strategic lamp placement, the surface will be either kept free from infection or be disinfected.

 The success of surface disinfection depends greatly on the consistency of the material to be disinfected.  In general, the UVC rays must directly strike the microbial contaminants to achieve lethal destruction.  If the bacteria or mold spores are hidden below the surface of a material or are not in the direct path of the UVC rays, they will not be destroyed.  Consequently, if the surface to be irradiated has rough areas or ridges or is granular, means must be taken to reduce any shadowing that may occur.

 The UVC exposure to ultraviolet necessary to kill bacteria is the product of time and intensity.  High intensities for a short period of time or low intensities for a long period of time are fundamentally equal in lethal action on microbial contaminants.

 UVC destroys only invisible organisms.  If you can see it, you can't kill it.  UVC is lethal to microorganisms; that is, those which are not visible to the naked eye.  It will not destroy insects or other such large organisms.  All types of microorganisms known to man including bacteria, virus and mold spores can be destroyed by germicidal ultraviolet rays.

 Ultraviolet will not penetrate most substances.  Meat, cloth and food will not be disinfected or sterilized by irradiating with ultraviolet since the rays do not go below these surfaces.  Even ordinary glass is opaque to UVC rays.  There are a few exceptions to this, notably clear water which does allow some penetration.  Also, some plastic films allow penetration.

 Not all materials have the same reflection factor for ultraviolet as they have for visible light.  In fact, some substances that are good reflectors of visible light are poor reflectors of UVC rays.  The design of a good reflector is paramount for an effective ultraviolet lamp fixture. Such reflective surfaces can intensify and control radiation.  The use of specular aluminum (alzak) or Fuller's "Solar Brite" reflective material enhances UV radiation.  Practical application has shown that properly designed fixtures with good reflectors are capable of doubling the effective radiation from an equivalent grid of bare lamps.

 Surface disinfection can be accomplished by using Fuller's Major Series devices.  This equipment is designed to direct UV rays properly and efficiently.  There are basically four types of reflectors used; namely - channel type, half-round type, louvered type, and closed and reflector type.  In addition to Fuller's standard UV equipment, we offer the services of our engineering department for custom applications.

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