Table 2. Effect of ClO₂ gas on B. atrophaeus biological indicator.

Sodium chlorite (ml/m3)	B. atrophaeus spores
	No. of sites with growth	No. of sites without growth
4.0	1	9
	0	10
10.0	0	10
	0	10
20.0	0	10
	0	10

Two independent experiments were performed under high-humidity conditions (75% to 85%) using a humidifier. Biological indicators were placed at 10 locations in the test room as shown in Fig. 1. ClO₂ gas was generated by mixing 3.35% sodium chlorite solution and 85% phosphoric acid at a 10:1 ratio. Experiments were carried out at 4.0, 10.0 and 20.0 ml/m³ of 3.35% sodium chlorite solution. After 24 h of ClO₂ gas exposure, indicator strips were incubated at 37°C for 48 h.