As explained above, for the rooms of a clean operating department, which are biological cleanrooms, the basis of classification is bacterial concentration, and this is the main point that distinguishes them from industrial cleanrooms.

3.4.1　Dynamic and Static States

Judging from the bacterial concentration standards in the various classifications given above, China's Architectural Technical Code for Hospital Clean Operating Department specifies the static state. The Hygienic Standard for Disinfection in Hospitals states that bacterial measurement involves "sampling during the period after disinfection and before medical activities," which also indicates that the data are static. Several foreign standards, on the other hand, should be regarded as dynamic standards. The British standard in Table 3.10 illustrates this most clearly: it stipulates that during surgery, the area within 30cm of the incision is subject to one standard, while the entire 3m×3m surgical area is subject to another. The Swiss standard, in its section "Evaluation of the Bacterial Count in Air," also points out that since the indoor bacterial count is affected by the number of people, their state of health, their movements, and the airflow organization (obviously this is a dynamic situation—Author), it is inappropriate to use the bacterial count at that moment to evaluate the cleanliness and sterility of the supply air.

The ratio of dynamic data to static data is called the dynamic-to-static ratio. It is generally taken as 3–5, and may be taken as 7 in larger cases.

3.4.2 Upper and Lower Limits

(1) Lower limit. Except for the German standard, which gives no data, and the American standard, which gives only one set of data, the standards of various countries all follow the WHO data. Among them, the lowest lower limit for clean operating rooms is airborne bacteria ≤200 CFU/m³, but this is a dynamic value. China's "Hygienic Standard for Disinfection in Hospitals" sets ≤200 CFU/m³ under static conditions for ordinary operating rooms. Obviously, even a Class Ⅲ clean operating room should have a higher degree of sterility than an ordinary operating room without air cleaning, so the "Architectural Technical Code for Hospital Clean Operating Departments," referring to the values of the American College of Surgeons standard, set the Class Ⅳ airborne bacteria concentration slightly below 200 CFU/m³, namely at 175 CFU/m³.

(2) Upper limit. The upper limits in the standards of various countries are all a dynamic 10 CFU/m³, while China's disinfection standard is a static 10 CFU/m³. The "Code" specifies a static 5 CFU/m³, which both reflects that the static value is lower than the dynamic one and gives consideration to the previous standard.

Therefore, although overall the bacterial concentration values in the "Code" are lower than those of the disinfection standard, they are still relatively lenient, and practice has proven that this remains an indicator that is easy to meet.

3.4.3 Relationship between Airborne Bacteria and Settling Bacteria

In the past, the standards of various countries all adopted a single standard—that for airborne bacteria. Practice has proven that, since the sampling instruments for the airborne method vary considerably and its operation is rather cumbersome, it is not practical. Both theory and practice have proven that in a room with supply air, particles below 5μm move following the airflow velocity, reaching more than 90% of the airflow velocity; therefore, wherever the airflow reaches, particles reach as well.

Sampling at the working point with the settling method better reflects the possible surface contamination at the working point; sampling at the working point with an airborne sampler, due to its large suction volume, does not necessarily draw exclusively the particles at that location. Therefore, settling concentration data accumulated over a long time can better reveal the patterns of the air cleaning system in contamination control and provide reference points and reference standards closer to actual conditions. This is why the Swiss hospital air-conditioning standard, in its section "Evaluation of the Bacterial Count in Air," points out that the settling method is recommended as a priority among the measuring devices, because it can indicate the source of microbial dispersal.

Taking the pharmaceutical industry as an example, the "Good Manufacturing Practice for Drugs" of the European Community and the European Union both broke through the framework of the World Health Organization (WHO) and formulated two standards, one for airborne bacteria and one for settling bacteria; China's standards and codes for hospital clean operating departments took the lead internationally in giving both bacterial concentration standards, which is a step forward.

In implementing the bacterial concentration standards, the airborne bacteria standard and the settling bacteria standard should be implemented separately; it is not advisable to convert between the obtained data, especially using the fixed coefficient "157," which is highly inappropriate and prone to contradictions.

When formulating bacterial concentration standards, however, they should be determined through conversion based on the relationship between airborne bacteria and settling bacteria.

The airborne bacteria concentration standard and the settling bacteria concentration standard given separately in China's standards and codes for hospital clean operating departments were established by first converting the settling bacteria concentration according to its relationship with airborne bacteria, while the airborne bacteria concentration was determined through comprehensive consideration based on the dust–bacteria relationship and with reference to foreign standards; see Tables 3.13–3.15.

Table 3.13 Calculation results according to Xu Zhonglin's theoretical formula (the equivalent bacterial diameter is taken as 10μm, close to the maximum)

Air cleanliness class Airborne bacteria concentration determined by the dust–bacteria relationship /(CFU/m³) Settling bacteria concentration calculated from the airborne bacteria concentration /[CFU/(φ90 dish·0.5h)]
Class 100 ≤3.5 ≤0.244
Class 10 000 ≤35 ≤2.4
Class 100 000 ≤110 ≤7.5
Class 300 000 ≤193 ≤12.8

Table 3.14　Values from the US NASA standard

Air cleanliness Given airborne bacterial concentration /(CFU/m³) Given settling bacterial concentration /[CFU/(φ90 plate·0.5h)]
Class 100 ≤3.5 ≤0.244
Class 10 000 ≤17.8 ≤1.24
Class 100 000 ≤88.4 ≤6.16

Table 3.15　Bacterial concentration standards given by the European Union (EU) Good Manufacturing Practice (GMP) for medicinal products

Air cleanliness Given airborne bacterial concentration /(CFU/m³) Given settling bacterial concentration /[CFU/(φ90 plate·0.5h)]
Class 100 (A) ≤1 ≤0.125
Class 100 (B) ≤10 ≤0.63
Class 10 000 ≤100 ≤6.25
Class 100 000 ≤200 ≤12.5

In the dynamic state, the bacterial equivalent diameter can be taken as $10mu m$, which is relatively safe. However, in the static state it should be smaller than this value, approximately $4.5mu m$; the settling bacterial concentration calculated on this basis is even smaller than that calculated with $10mu m$, by $dfrac{10^2}{4.5^2 times 1.3} = dfrac{1}{3.8}$.

The bacterial concentrations given in China's standard, calculated according to this principle, are listed in Table 3.16.

Table 3.16　Calculation results for the grade classification of China's standard

Grade Cleanliness of operating area Specified airborne bacterial concentration /(CFU/m³) Calculated settling bacterial concentration /[CFU/(φ90 plate·0.5h)] Specified settling bacterial concentration /[CFU/(φ90 plate·0.5h)]
Ⅰ Class 100 ≤5 ≤0.09 ≤0.2
Ⅱ Class 1 000 ≤25 ≤0.45 ≤0.75
Ⅲ Class 10 000 ≤75 ≤1.4 ≤2
Ⅳ Class 300 000 ≤175 ≤3.3 ≤5

It can be seen that the specified settling bacterial concentration is enlarged by a factor of 1.5 to 2 compared with the calculated values.

【Reference】　Tables 3.17–3.22 list a summary of the results of several bacterial concentration tests in the clean operating department of a certain traditional Chinese medicine hospital.

Table 3.17　Test results of the provincial capital epidemic prevention station for the clean operating department of a certain traditional Chinese medicine hospital

(March 24, 2001, 30 min, φ90 plate, with reference to the military standard)

Room No. Class Measuring point 1 Measuring point 2 Measuring point 3 Measuring point 4 Measuring point 5 Result/(CFU/plate) Conclusion
1 100 000 0 1 0 1 0 2 √
2 10 000 1 1 0 2 0 4 √
3 10 000 0 1 1 1 0 3 √
4 1 000 0 1 0 0 0 1 √
5 1 000 0 0 0 0 0 0 √
6 10 000 2 0 0 0 0 2 √
7 10 000 0 2 0 0 0 2 √
8 100 000 3 0 1 1 5 √
9 100 000 0 2 2 4 √
Dressing room 100 000 1 0 2 3 √
Instrument room 100 000 2 0 2 4 √
Recovery room 100 000 1 1 0 2 √
Corridor 100 000 2 3 0 1 1 7 √

Table 3.18　Self-inspection results by the hospital for the clean operating department of a certain TCM hospital (I)

(March 26, 2001, 5 min, φ90 petri dish, with reference to the Hygienic Standard for Disinfection in Hospitals)

Room No. Class Measuring point 1 Measuring point 2 Measuring point 3 Measuring point 4 Measuring point 5 Result/(CFU/m³) Conclusion
1 100 000 3 0 0 157 ×
2 100 00 2 0 0 0 0 62 ×
3 10 000 1 0 0 0 0 31 ×
4 1 000 0 0 0 0 0 0 ✓
5 1 000 0 0 0 0 0 0 ✓
6 10 000 0 0 0 0 0 0 ✓
7 10 000 0 0 0 0 0 0 ✓
8 100 000 0 0 0 0 ✓
9 100 000 0 0 0 0 ✓
Dressing room 100 000 0 0 0 0 0 0 ✓
Corridor 100 000 1 0 0 0 39 ×

Table 3.19　Self-inspection results by the hospital for the clean operating department of a certain TCM hospital (II)

(March 27, 2001, 5 min, φ90 petri dish, with reference to the Hygienic Standard for Disinfection in Hospitals)

Room No. Class Measuring point 1 Measuring point 2 Measuring point 3 Measuring point 4 Measuring point 5 Result/(CFU/m³) Conclusion
1 100 000 0 0 0 0 0 0 ✓
2 10 000 0 0 0 0 0 0 ✓
3 10 000 0 0 1 0 0 31 ×
4 1 000
5 1 000
6 10 000
7 10 000
8 100 000
9 100 000
Dressing room 100 000
Corridor 100 000

Table 3.20　Self-inspection results by the hospital for the clean operating department of a certain TCM hospital (III)

(March 28, 2001, 5 min, φ90 petri dish, with reference to the Hygienic Standard for Disinfection in Hospitals)

Room No. Class Measuring point 1 Measuring point 2 Measuring point 3 Measuring point 4 Measuring point 5 Result/(CFU/m³) Conclusion
1 100 000 0 0 0 0 ✓
2 10 000 1 0 0 0 0 31 ×
3 10 000 0 0 1 2 0 94 ×
4 1 000 0 0 1 0 0 31 ×
5 1 000 0 0 0 0 0 0 ✓
6 10 000 0 2 1 0 0 157 ×
7 10 000 0 0 0 0 0 0 ✓
8 100 000 2 0 1 157 ×
9 100 000 0 1 1 104 ×
Dressing room 100 000 0 0 0 0 0 0 ✓
Corridor 100 000 0 0 0 0 0 0 ✓

Table 3.21　The fourth part of the hospital's self-inspection results for the clean operating department of a certain TCM hospital

(March 29, 2001, 5min, φ90 plate, with reference to the Hygienic Standard for Disinfection in Hospitals)

Room No. Class Measuring point 1 Measuring point 2 Measuring point 3 Measuring point 4 Measuring point 5 Result/(count/m³) Conclusion
1 100 000 0 0 0 0 √
2 10 000 0 0 0 1 0 31 ×
3 10 000 0 1 0 0 0 31 ×
4 1 000 0 0 0 0 0 0 √
5 1 000 0 0 0 0 0 0 √
6 10 000 0 0 0 0 0 0 √
7 10 000 0 0 0 0 0 0 √
8 100 000 1 0 0 52 ×
9 100 000 0 0 0 0 √
Dressing room 100 000 0 0 0 0 √
Corridor 100 000 1 0 0 2 117 ×

Table 3.22　The hospital's self-inspection results for the clean operating department of a certain TCM hospital

(April 9, 2001, 20min, φ90 plate, with reference to the Hygienic Standard for Disinfection in Hospitals)

Room No. Class Measuring point 1 Measuring point 2 Measuring point 3 Measuring point 4 Measuring point 5 Result/(count/m³) Conclusion
1 100 000 1 7.8 √
2 10 000 1 7.8 √
3 10 000 2 15.7 ×
4 1 000 1 7.8 √
5 1 000 2 15.7 ×
6 10 000 1 7.8 √
7 10 000 2 15.7 ×
8 100 000 1 7.8 √
9 100 000 2 15.7 ×
Dressing room 100 000 0 0 0 / √
Corridor 100 000 1 0 0 2 / √

In the conclusion columns of Tables 3.17–3.22 above, × indicates unqualified and √ indicates qualified.

It can be seen that, when tested and evaluated by the provincial capital's health and epidemic prevention station according to the provisions of the military standard, all results were qualified, whereas on the other hand, when measured and evaluated according to the disinfection hygiene standard, some rooms were unqualified—a contradiction arose. Since these measurement and evaluation methods are fairly representative, a specific analysis is made as follows:

(1) The provincial capital's health and epidemic prevention station misunderstood the testing method of the military standard. The provincial evaluation took the total colony count of all plates as the criterion, rather than the average of the 30min sampling counts of the plates. In the military standard, the maximum allowable for Class 100, Class 1 000, Class 10 000 and Class 100 000 The colony counts were 1, 2, 5, and 10 (CFU/plate), respectively. Therefore, the entry in the result column is not only qualified but should be even smaller than the values in the table; that is, although it should be rated as qualified, the calculation method was erroneous.

(2) The hospital's self-inspection method complied with the provision of the Hygienic Standard for Disinfection in Hospitals of sampling for 5 min, and the calculation was also carried out in the manner given by that standard, namely

$$frac{text{Total colony count}}{text{Number of measuring points}} times 157.2 text{ CFU/m}^3$$

For example, for Operating Room No. 1 of Class 100 000 in Table 3.19:

$$frac{3}{3} times 157.2 = 157.2 text{ CFU/m}^3$$

The result was taken as 157 CFU/m³.

Since the provincial evaluation regarded all clean operating rooms as laminar flow rooms (as mentioned earlier), with a qualification criterion of $leqslant 10$ CFU/m³, the measurer accordingly judged this measurement result as unqualified. If, as recommended by WHO, the Class 100 000 clean operating room were treated as a general aseptic operating room inferior to laminar flow operating rooms, with a qualification criterion of 200 CFU/m³, then the result should have been qualified.

This judgment method of regarding all clean operating rooms as laminar flow rooms is obviously incorrect. According to this understanding, as long as 1 out of the 5 plates has a single colony, the result would be

$$frac{1}{5} times 157.2 = 31.4 text{ CFU/plate} > 10 text{ CFU/m}^3$$

and all would be unqualified; every plate would have to show 0.

So this measurement was also judged incorrectly.

(3) In the test by the municipal health and epidemic prevention station, the sampling time was merely extended to 20 min (4 times 5 min), so the calculation became:

$$frac{text{Total colony count}}{dfrac{20}{5} times text{Number of measuring points}} times 157.2 text{ CFU/m}^3$$

For example, for Operating Room No. 3 of Class 100 00 in Table 3.22:

$$frac{2}{dfrac{20}{5} times 5} times 157.2 = 0.1 times 157.2 text{ CFU/m}^3 = 15.7 text{ CFU/m}^3 > 10 text{ CFU/m}^3$$

It was judged unqualified, committing the same error as the hospital's self-inspection.

In summary of the above analysis, if assessed according to the military standard, the test results of the provincial capital's epidemic prevention station are correct (if assessed according to the Code, some rooms are unqualified).