BS ISO 16000-36:2018 pdf download – Indoor air Part 36: Standard method for assessing the reduction rate of culturable airborne bacteria by air purifiers using a test chamber
6.1 Preparation and maintenance of stock culture
Rehydrate the lyophilised reference culture of the test bacteria according to the manufacturer’s instructions. Transfer the rehydrated reference culture to a conical flask containing a defined volume of nutrient broth medium ( Incubate for (18 ± 2) h at (36 ± 2) °C in an incubator (5.1.6) while gently shaking. Add the same volume of 20 % (volume fraction) sterile glycerol or 10 % (volume fraction) dimethylsulphur oxide (DMSO), to the bacterial suspension to attain 10 % (volume fraction) glycerol or 5 % (volume fraction) DMSO suspension and mix well. Distribute the aliquots into plastic tubes of approximately 0,5 ml and store at (−70 ± 10) °C in a cryogenic freezer (5.1.7) for a maximum of two years.
6.2 Preparation and maintenance of working cultures of the test bacteria on agar plates
Prepare a working culture of the test bacteria from the stock culture (6.1). Equilibrate the frozen stock culture to room temperature (15 to 30) °C and inoculate the bacterial suspension to a nutrient agar plate ( in such a way that single colonies are obtained. After cultivation, store the plates at (5 ± 3) °C for not longer than one month.
6.3 Preparation of working culture suspensions Inoculate (50 ± 5) ml of nutrient broth media ( in a conical flask of 300 ml with one to five colonies from the working culture agar plates (6.2) and incubate for (18 ± 2) h at (36 ± 2) °C while gently shaking. Obtain a concentration of about 1,0 to 3,2 × 10 3 cfu/ml (equivalent to 300 “full holes” in a 300 impactor lid, if 100 l were impinged) for testing. If the concentration of the test bacterial suspension is more than 1,0 to 3,2 × 10 3 cfu/ml, dilute this suspension with physical saline solution ( through 10‑fold dilutions. Store the culture suspension at (5 ± 3) °C and use within 4 h. To test the concentration of the bacteria in the suspension, inoculate the prepared suspension on nutrient agar media through 10‑fold dilutions and, after incubating at (36 ± 2) °C for (18 to 24) h, count the colonies on the plates.
7 Procedures
7.1 General Prevent any bacterial contamination by preparing and handling the test bacteria and use a microbiological safety cabinet (5.1.8). The test is performed in two steps. In step 1 (see 7.2) the concentration of the test bacteria is measured without operating the air purifier, then in step 2 (see 7.3) with operation of the air purifier. The test is only valid if the conditions in 8.2 are met and the test (step 2) was performed in the time period when the decay rate in step 1 remained below 50 % (see Annex B). If these conditions are not met, the test (step 1 and step 2) shall be repeated.
The test is performed subsequently with both test bacteria.The suspension of the respective test bacterium used in step 2 is the same as the suspension used in step 1.
7.2 Step 1 — Measurement of the concentration of culturable test bacteria, c i , without operating the air purifier
7.2.1 General
In step 1, the concentration of the test bacteria is measured without operating the air purifier.
7.2.2 Preparation of the air purifier and the test chamber
Place the air purifier in the middle of the chamber. Clean gently the front surface of the air purifier two or three times with a piece of gauze or cotton ball soaked in 70 % ethanol (5.1.12) and dry it completely.
If ethanol is not suitable for the surface materials of the air conditioner, or causes other destruction that might affect the test results, use another decontamination method.
The temperature and relative humidity inside the test chamber shall be maintained at:
— temperature: (23 ± 2) °C;
— humidity: (50 ± 5) % RH.
Before the test, decontaminate the interior space of the chamber, e.g. by using an UV lamp.
Insert three or more impactors containing the agar plates with nutrient agar into the test chamber.
Decontaminate the impactors with 70 % ethanol (5.1.12) or using another appropriate method.
NOTE Using more than three measurement points can be useful to demonstrate the homogenous distribution of the bacteria in test chambers with higher volumes.BS ISO 16000-36 pdf download.