Joint International Conference on Long-term Experiments ...

3:1 to 5:3 . In the following experiments, fumigations were carried out by using a mixture of
17.8 ml of Formalin and 8.9 g of potassium permanganate per m 3 of air space in a lowsecurity
area at room temperatures of 16, 24, and 300C. In preliminary experiments, room
air samples were taken from each of four positions, including the ceiling and the floor, and
HCHO levels were determined by chemical assay. Because no differences in concentration
were observed between any positions, all results from the sampling points were averaged.
HCHO levels were also measured after vaporization of 12.5 ml of Formalin (70% of that
used in the Formalin-permanganate fumigations to allow for losses due to permanganate
oxidation) on a hot plate at a room temperature of 27°C.
Survival of B. subtilis after fumigation by the Formalin-permanganate method. B.
subtilis spores survived on some rods located at various places in a low-security area during
a 24- h Formnalin-permanganate fumigation at an initial temperature of 1800. Viable counts
of 2 x 106 were obtained from control rods, but only two of nine rods exposed in the treated
area were sterile; viable counts of 20 to 600 were obtained from the others. It is clear that,
although this procedure was fairly effective, sterilization was not achieved.
Two further experiments were carried out in a sealed jar at 20°C in controlled HCHO vapor
levels of 150 and 300 Ag/liter of air, with relative humidity maintained at approximately
100%. Exposure to 150, ug of HCHO per liter of air did not result in sterilization even after
exposure for 6 h. Exposure to 300, Ag/liter was much more effective, and no viable spores
were detected at 3 h.
Use of electric vapor generator. The results from several fumigations are presented, using
the electric vapor generator and different amounts of Formalin in a low-security area at
different initial temperatures. In procedure 1, persistent HCHO levels similar to those
obtained by the hot plate vaporization method were achieved. No viable B. subtilis spores
were detected after 24 h of exposure on the 18 spore rods located in the main laboratory
area, but a 0.5% survival was detected on a rod located in a closed cupboard. The fumigant
level in the cupboard was 160, ug/liter after 6 h. Procedure 2 was carried out with the same
volume of Formalin and an initial room temperature of 15°C. No surviving spores could be
detected after 7 h of exposure on 12 spore rods located around the room, but two located in
cupboards showed a survival of 1%. Procedures 3 through 5, which were carried out for
different times and temperatures and with varying amounts of Formalin, are also described.
In procedure 6, a mixture of paraformaldehyde and water equivalent to 8.9 ml of Formalin
per m 3 of air was used. Again, no surviving spores could be detected from rods distributed
throughout the main laboratory area in any of the procedures. All subsequent fumigations
were carried out with 3.7 g of paraformaldehyde per m3 of room volume, which is
converted to HCHO equivalent to that present in 8.9 ml of Formalin.
Humidity in each area was increased to 80%, a level which has been shown to increase
the effectiveness of fumigation by causing HCHO to dissolve in a film of moisture around
microorganisms, where it is more bactericidal than in vapor form .Use of Formalin at a
room temperature of 200C would have contributed approximately 30% to the relative
humidity. More reliable humidity control could be achieved with paraformaldehyde, which
was also more convenient to use. Use of electronic HCHO monitor. The electronic monitor
was developed because of the time involved in chemical assays of air samples. When the
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