Saturday, 26 September 2020

Ultraviolet lamp in operation, cleaning self-catering cottage

 In these times of Covid-19, we now use the ultraviolet-c lamp in the process of  cleaning. We first suit-up in full body PPE equipment, including a respirator, prior to entering the cottage. As part of the procedure we assume the departing guests could have been infected asymptomatically with the virus. We then progress around the rooms in the cottage giving a timed exposure to each room from the Ultraviolet-C light to help sterilize the environment.

UV-C Lamp sterilizing kitchen


Here you can see the lamp in operation in the kitchen during a recent cleaning session. We move it around during exposure process to avoid shadows and ensure even coverage. During the operation of the lamp we normally keep out of the room and control the lamp using a remote power switch. Usually before entering the room we switch off the lamp. When there is a need to be in the room with the lamp on, we wear full body protection and also a full face visor tested to be safe against UV-C light. We also limit time in front of the lamp. The lamp in the picture is 72 watts/230 VAC. Close up to the lamp, at 30 cm, you'd receive the maximum permitted dose in less than 30 seconds. We also carry dosimeter badges which are checked before and after exposure. 

We have a specialist UV-C meter which allows us to accurately measure the dosage given around the room, and also the impact of UV-C reflection from surfaces. We use the meter to "calibrate" the room and thus verify an appropriate exposure time for sterilization in each room. Typically in our case this is about 20 minutes total exposure time per room to achieve 40 millijoules per sq cm dosage.

Using UV-C light avoids the general usage of persistent biocide chemicals as a film on all surfaces and in the air. This may occur with biocide/hypochlorous fogging disinfection techniques. We don't wish to expose our guests or cleaning staff to these chemicals.  However we do supplement the UV-C by wipedown with a disinfectant on high touch areas and work surfaces. Surfaces of electrical equipment, buttons and switches are sterilized using non-conducting 100% isopropyl alcohol.

The Philips TUV discharge tubes in the lamp have a surface treatment which suppresses the light wavelength which generates ozone from oxygen in the air. However in operational use, there is a tiny amount of ozone produced. You can smell it as a faint odour. While ozone is a very powerful disinfectant, it is not good to breath in. So we ventilate the rooms with plenty of fresh air during and after the process. We also make sure that guests are not allowed in to the cottage until at least an hour after the UV process to allow any residual ozone to revert to oxygen.

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