Ethylene oxide sterilisation

Eig. 8. An ethylene oxide sterilisation vessel (autoclave) and supportive system. 

Fig. 9. Ethylene oxide sterilisation 4-h cycle, 12/88 12 wt % ethylene oxide/88 wt % chlorofluorocarbon (Freon 12), where the horizontal line represents standard barometric pressure A, preconditioning and humidification at 87.8—94.55 kPa, 30—40 min B, exposure for 3/4 h at 55.17—68.95 kPa above standard barometric pressure C, air washes at 81.04—87.8 kPa, 20 min. To convert kPa to psi, multiply by 0.145.

This entails residues related to ethylene oxide sterilisation, and physical and chemical changes when gamma irradiation or accelerated electrons are employed, particularly when plastics are involved. It should be noted that plastics include lacquers, enamels, certain adhesives, etc. Surface analysis is emerging as a critical evaluation for any treatment process. The need to establish the purity/impurity of packaging materials will also become necessary for most sterile products. 

Detailed provisions relating to sterility testing and ethylene oxide sterilisation of therapeutic goods are set out in Appendices C and E respectively. 

Biological indicators, (i.e., preparations of bacterial cultures, usually spores of selected resistant strains) are much less reliable than physical monitoring methods (except in ethylene oxide sterilisation). 

Costa L., K. Jacobson, P. Bracco, and E.M. Brach del Prever. 2002. Oxidation in ethylene oxide sterilised UHMWPE. Biomaterials 23 1613-1624. 

T. Zislis et al., Scanning electron microscopic study of In Vitro Toxicity of Ethylene Oxide Sterilised Bone Repair Materials, Interim Report July 87—March 88, Army Inst, of Dental Research, Washington, District of Columbia, USA. 

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. 

Low humidity ethylene oxide gas sterilisa tion procedures and moisture-proof packaging for polyglycoHc acid products are necessary because of the susceptibihty to degradation resulting from exposure to moisture and gamma sterilisation. 

R. R. Ernst, Industrial Sterilisation Ethylene Oxide Gaseous Sterilisation for Industrial Applications Duke University Press, Durham, N.C., 1973. 

Humidity can be a problem. Whereas it was shown (284) that 33% RH was best for spore inactivation, and that at least 30% RH was needed for effective sterilisation (285), dried spores are difficult to kill, and the spore substrate material and wrappings compete with the spore for the available moisture (286). Therefore, the relative humidity is adjusted to 50—70% to provide sufficient moisture for the spores to equiUbrate. The exposure time depends upon the gas mixture, the concentration of ethylene oxide, the load to be sterilised, the level of contamination, and the spore reduction assurance requited. It may be anywhere from 4—24 hours. In a mn, cycles of pre-conditioning and humidification, gassing, exposure, evacuation, and air washing (Fig. 9) are automatically controlled. 

This is a special chemical effectively used for column bioreactors. It is a volatile compound and strong oxidising agent. It boils at ambient temperature, therefore the solution of ethylene oxide (liquid phase) must be stored in a refrigerator (4 °C). An excellent oxidising agent such as a 3% sodium hypochlorite is used for chemical sterilisation of equipment. 

The autoinflammation temperature of a 50/50 mixture of ethylene oxide and air that is around 460°C lowers to between 416-251 C when ethylene oxide comes into contact with certain insulation materials (that can be found in sterilisation chambers where this oxide is used). 

Salmona et al. [66] used El and CIMS to identify benzothiazole derivatives leached into injections by rubber plunger seals from disposable syringes. One of the compounds was used as a rubber vulcanisation accelerator, and four others were formed during syringe sterilisation with ethylene oxide. Applications of hyphenated chemical impact mass-spectrometric techniques are described elsewhere GC-MS (Section 7.3.1.2), for polar and nonpolar volatile organics, SFC-MS (Section 13.2.2) and TLC-MS (Section 7.3.5.4). 

Cold sterilisation can be carried out with a mixture of 90% carbon dioxide and 10% ethylene oxide, the carbon dioxide has a stabilising effect on the ethylene oxide and reduces the risk of explosion. 

Hazards attendant on use of ethylene oxide in steriliser chambers arise from difficulties in its subsequent removal by evacuation procedures, owing to its ready absorption or adsorption by the treated material. Even after 2 evacuation cycles the oxide may still be present. Safety is ensured by using the oxide diluted with up to 90% of Freon or carbon dioxide. If high concentrations of oxide are used, an inert gas purge between cycles is essential [7], The main factors in safe handling... 

Baratov, A. N. et al., p.24 of BLL translation (628.74, issued 1966) of Russian book on Fire Prevention and Firefighting Symposium . The addition of bromomethane to ethylene oxide (used for germicidal sterilising) to reduce the risk of explosion is relatively ineffective, the inhibiting concentration being 31.2, as against 5.8 for hexane and 13.5 vol.% for hydrogen. 

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