Tuesday, May 15, 2012
Flammable Cabinets for Ethylene Oxide Must be Vented.
Many hospitals use ethylene oxide (EtO) for low temperature sterilization despite the faster cycle times of competing technologies using hydrogen peroxide or ozone because of its great efficacy, broad application (lumens, cellulose products can all be sterilized) and much less damage to certain medical devices than the oxidative sterilants. EtO sterilization used to be supplied in tanks, blended with non-flammable balance gases, but the modern trend is to use single use cartridges with about 100 to 170 g of 100% EtO in them. These single use cartridges greatly improve safety compared to the older tanks because if there is a leak the amount of EtO involved is much smaller and cylinders no longer have to be changed. As with all the sterilant gases, EtO poses health risks for anyone exposed to it. It has the same OSHA permissible exposure limit (PEL) and hydrogen peroxide, (1 ppm calculated as an 8 hr time weighted average (EtO 29 CFR 1910.1047, H2O2 29 CFR 1910.1000 Tbl Z-1 because of EtO’s toxicity and carcinogenicity. In addition, EtO is a flammable low boiling point liquid (BP = 12 oC) and so should be stored in an NFPA approved flammable cabinet (NFPA 30). Most hospitals that we visit do store their single use cartridges in flammable cabinets, but a surprising number do not vent the cabinets. These single use cartridges often seep small amounts of EtO. If the cartridges were in the open, the EtO seepage though not good would be dispersed into the air and with the high air turn over in most sterile processing departments, not pose a great threat. However, if the cartridges are in an unvented flammable cabinet, the EtO that seeps from the cartridges can accumulate within the cabinet to be released only when the door is opened. We have seen a surprisingly large number of unvented flammable cabinets being used to store EtO single use cartridges. Facilities are using flammable cabinets because of the flammability of EtO, but are ignoring the toxicity of EtO. Hospitals that use EtO are required to have a dedicated exhaust and so in most cases the cost of connecting the EtO flammable cabinet to the exhaust is minimal. If the EtO flammable cabinet in not vented then the cost in terms of employees health in the long term may be much larger. It is not just ChemDAQ that is raising this concern, 3M, one of the major suppliers of these single use cartridges also recommends the use of vented flammable cabinets. Most flammable cabinets have vents built into the side of them by the manufacturer, and so exhaust ducts can easily be connected to the flammable cabinets using standard plumbing fixtures. It is important that the cabinets be actively vented, i.e. the gas inside the cabinet is sucked out. Simply opening the vents on the side of the cabinet and relying on air diffusion does not suffice since air diffusion is relatively slow especially if there are flame arrestor grids in the vent holes. In summary, EtO cartridges should be stored in a flammable cabinet, but since EtO has such a low PEL, the cabinet should be actively vented to prevent exposure of workers using the EtO cartridges to EtO.