Ultraviolet bactericidal exposure of the air is carried out using ultraviolet radiation equipment, the principle of which is based on passing an electric discharge through a rarefied gas (including mercury vapor), which is located inside a sealed enclosure, resulting in radiation.
Emitting equipment is a bactericidal lamp and radiation equipment. A bactericidal lamp is an artificial radiation source, the spectrum of which is mainly bactericidal radiation in the wavelength range of 205-315 nm. The greatest distribution, due to the highly efficient conversion of electric energy into radiation, was obtained by mercury 122 low-pressure lamps, in which the process of electric discharge in an argon-mercury mixture passes into radiation with a wavelength of 253.7 nm. These lamps have a long service life – 5000 – 8000 hours. High pressure mercury lamps are known which, with small overall dimensions, have a large unit power – from 100 to 1000 W, which in some cases reduces the number of irradiators in a bactericidal installation. On the other hand, they are not very economical, have low bactericidal efficacy and a service life of 10 times less than low-pressure lamps, and therefore have not been widely used.
A number of the largest electric lamp companies (Philips, Osram, Radium, Sylvania, etc.) are currently engaged in the development and production of UV lamps for photobiological action plants.
For a more rational use in practice of bactericidal lamps, it is advisable to incorporate them into bactericidal irradiators.
A bactericidal irradiator is an electrical device consisting of a bactericidal lamp or lamps, ballasts, reflective fittings, parts for fixing lamps and connecting to the network. According to their design, the irradiators are divided into three groups: open (ceiling or wall), shielded (wall, using a reflector), closed (recirculates). A combination of open and shielded bactericidal lamps is also used – combined irradiators. In open, shielded and combined irradiators, the direct bactericidal flow from the lamps and the reflector (or without it) covers a wide area in space up to a solid angle of 4 pi. Open irradiators are intended for the disinfection of the room only in the absence of people or during their short stay in the room.
• Open irradiators are usually attached to the ceiling or wall, combined – to the wall and can be with or without reflectors. In open irradiators, a direct bactericidal flow covers a wide area in space up to a solid angle. They are intended for the process of disinfection of premises only in the absence of people or during their short stay.
• In closed irradiators, the lamps are located in a small closed enclosure of the irradiator and the bactericidal flow does not go outside the enclosure, therefore, irradiators can be used when people are in the room. The energy of the bactericidal stream deactivates most viruses and bacteria that enter the indoor unit along with the air stream. Diffusers are provided in the body of the irradiator, through which, with the help of the built-in fan, air enters the device where it falls under the ultraviolet radiation source in the closed space of the indoor unit, and then returns to the room. Closed irradiators are usually placed on the walls of the premises, evenly around the perimeter, in the direction of movement of the main air flows (often near heating appliances) at an altitude of 1.5-2.0 m from the floor level.
• Combined irradiators are usually provided with two bactericidal lamps, separated by a screen so that the flow from one lamp is directed only to the lower zone of the room, from the other to the upper zone. Lamps can be switched on together and individually.
The bactericidal unit includes a group of bactericidal irradiators. It can also be a system of supply and exhaust ventilation, in the elements of which bactericidal lamps are built in to supply disinfected air to the room. The level of bactericidal effectiveness of the installation is set in accordance with the medical and technical task for its design.
The duration of the bactericidal installation, at which the required level of bactericidal effectiveness is achieved, varies depending on the type of irradiator: for closed irradiators 1-2 hours; for open and combined 0.25-0.5 hours; for systems of supply and exhaust ventilation 1:00 and more.
A separate class of devices is bactericidal equipment as part of a forced-air ventilation (air conditioning) installation, which makes it possible not to install devices in separate rooms, but to service entire floors. These are the so-called air disinfection units. They are produced as part of air conditioners of general industrial, medical and hygienic design. An air disinfection module usually consists of a specific number of bactericidal lamps and an air filter.