Low-temperature steam and formaldehyde

Low-temperature steam and formaldehyde Gas concentration 15-100 mgl" Steam admission to 73°C 40-180min sterilizing time depending on type of process... 

Low temperature steam and formaldehyde Reactive chemical Indicator paper impregnated with a formaldehyde-, steam- and temperature-sensitive reactive chemical which changes colour during the sterilization process Gas concentration, temperature, time (selected cycles)... 

Fig. 20.8 Typical operating cycle for low-temperature steam and formaldehyde treatment.

Disposable equipment should not be re-sterilized or re-used. 2. Ethylene oxide is a difficult process to control and the Department of Health discourages its use in hospitals. 3. Low temperature steam with formaldehyde is of value in the sterilization/disinfection of some heat-sensitive materials. 4. Chemical agents, e.g. gluteraldehyde, hypochlorite. 

Table 20.3 Relative merits of ethylene exide and low-temperature steam formaldehyde (LTSF) pmcesses... 

Low temperature steam (73°C) and formaldehyde (12mg - ) Bacillus stearothermophilus 5min... 

Hoxey EV, Soper CJ, Davies DJG. 1985. Biological indicators for low temperature steam formaldehyde sterilization Effect of defined media on sporulation, germination index and moist heat resistance at 110 degrees C of bacillus strains. J Appl Bacteriol 58 207-214. 

To say that ethylene oxide sterilisation is the method of choice is also not universally accepted in England. I have made special representations to Dr. Kelsey of the Central Public Health Laboralories at Colindale on two occasions over the last four years. On both occasions he has produced more objections to ethylene oxide sterilisation than attractions. Dr. Kelsey has sent me considerable literature and references in his own work against the efficacy of ethylene oxide sterilisation. Rather than support the use of ethylene oxide sterilisation Dr. Kelsey apparently would prefer to popularise sterilisation by low temperature steam combined with formaldehyde vapour for plastics materials and other substances likely to be damaged by dry heat or conventional autoclaving. 

Formaldehyde gas for use in sterilization is produced by heating formalin (37% wA aqueous solution of formaldehyde) to a temperature of 70-75°C with steam, leading to the proeess known as LTSF. Formaldehyde has a similar toxicity to ethylene oxide and although absorption to materials appears to be lower similar desorption routines are leeommended. A major disadvantage of formaldehyde is low penetrating power and this limits the packaging materials that eanbe employed to principally paper and eotton fabrie. 

The formaldehyde is charged into the reactor and the pH value has to be adjusted. Urea is then added and the mixture will be heated up to the reaction temperature. The reactor consists of a stirred kettle based on load cells and is equipped with heating jacket and internal cooling coils. Heating is carried out with low pressure steam. An efficient anchor agitator ensures good heat transmission and uniform reaction conditions. The reaction proceeds in several steps at 70°-100°C. 

From our own experience, series of various steels (for low and high temperature) were tested under reaction conditions (for example, for methane and methanol steam reforming and partial oxidation to formaldehyde) either as raw materials or after protective layer coating, including the soldering/brazing materials used for assembly. 

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