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Instruction on the determination of the efficiency of the air sanation by the UV irradiation

Planting of the air is performed on beef-extract agar or special agar in Petri dish in Krotov’s device (fig. 3.3) before irradiation (exposure) to estimate the air sanation efficiency. The irradiation is performed using the bactericidal lamps LB-30 or mercury-quartz lamps in accordance with the pre-calculated exposure. Replanting (secondary planting) of the air in Petri dish is done after the exposure. Dishes are incubated in the thermostat during 24 hours at the temperature of 37⁰C. The number of colonies after the incubation is calculated in both Petri dishes before and after the exposure.

The air contamination with the microbes is estimated by determination of microbe air contamination index (microbe number) (the number of microorganisms per 1 m³ of the air) and the Staphylococcus hemalyticus population.

Microbe number is calculated using the following formula:

M.n. =

where: М.n. – number of microbes in 1 m³ of the air;

А – number of colonies in Perti dish;

Т – duration of air sampling in minutes.;

V –air transmission speed of Krotov’s device, l/min.

Efficiency degree and efficiency coefficient characterize the bactericidal effect of the UVR. Efficiency degree represents the percentage of decrease in the number of microbes. Efficiency coefficient represents by how many times the microbe number has decreased in the same air volume (colonies number disparity in Petri dishes before and after air exposure).

Fig. 3.3. Krotov’s device for bacterial research of the air

(1 – cone crack; 2 – rotating disk; 3 – rheometer)

Sanation is considered effective if the efficiency degree is 80%, and the efficiency coefficient is not less than 5. (Efficiency degree is the ratio of microbe number difference before and after exposure to microbe number before exposure in %. Efficiency coefficient is the number, which represents by how many times the number of colonies has decreased after the exposure).

Microbe number after the air exposure is compared to the allowed air contamination index for premises (table 3)

Table 3