Table 1. Number of bacterial CFU/m3 air at different sampling time of day at different time of exposure.
| Petri dish exposure time (Min) | Sampling time | Sampling sites |
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| Ketofurdessa Technology Library | Agriculture and Veterinary Medicine Library | Health Science Library | Social Science Library | Technology Library | Education Library | Law Library | FBE Library | ||
| 30 | 8:30 a.m. | 498 | 1 101 | 2 123 | 760 | 1 887 | 1 415 | 1 153 | 1 625 |
| 4:00 p.m. | 367 | 944 | 1 887 | 682 | 1 573 | 944 | 865 | 1 389 | |
| 60 | 8:30 a.m. | 799 | 1 678 | 2 202 | 839 | 2 333 | 1 730 | 1 756 | 1 730 |
| 4:00 p.m. | 773 | 1 468 | 2 045 | 708 | 1 913 | 1 101 | 1 546 | 1 546 | |
| 90 | 8:30 a.m. | 856 | 2 097 | 2 595 | 865 | 2 429 | 1 992 | 1 844 | 1 879 |
| 4:00 p.m. | 830 | 1 905 | 2 525 | 751 | 1 975 | 1 538 | 1 651 | 1 782 | |