I am concerned about the safety of my EtO sterilized goggles. What can you tell me about EtO exposure levels?
The permissible levels of EO residuals are specified in ISO 10993 7: 2008, Biological evaluation of medical devices Part 7: Ethylene oxide sterilization residuals. There are two residual chemicals of concern, namely Ethylene Oxide (EO) and Ethylene Chlorohydrin (ECH). As part of the sterilisation validation, we tested for residuals and found the average levels to be EO = 0.43mg and ECH = 0.06mg per goggle. Approximately 6% of the goggle is in contact with the wearer so the residuals that are transferrable to the wearer are EO = 0.026mg and ECH = 0.004mg. The standard defines three exposure categories for the device then assigns safe exposure limits for each category. The categories are: a) Limited exposure: devices whose single or multiple use or contact is likely to be up to 24 h; b) Prolonged exposure: devices whose single, multiple, or long-term use or contact is likely to exceed 24h but not 30 days; c) Permanent contact: devices whose single, multiple, or long-term use or contact exceeds 30 days. With a product like the goggles the time worn in total is taken into account, not the time that each goggle is worn. Given the definitions above, a typical worker is going to exceed 30 days so we need to treat the exposure as permanent contact. NOTE: ISO 10993-7 defines Lifetime as 25,000 days. So, our EtO sterilised goggles are well within the limits set by ISO with the actual results being about a quarter of the allowable levels. With regard to FDA requirements, the only document dealing with residuals is a draft guidance document from June 1978, which never progressed beyond the draft stage. In that document the limits were set at 250 parts per million for EO and also for ECH. We have looked up several guidance documents for specific medical devices that are EO sterilised and in those there are references to ISO 10993-7 for the evaluation of residuals. That guidance looks to have started in about 2000 and ISO 10993-7 is now listed on the FDA site as a Recognised Consensus Standard, which means that it can be used in claims of compliance in 510(k) submissions. We have not found anything on the FDA website which discourages the use of Ethylene Oxide as a method of sterilisation. In fact ISO 11135-1, which is the standard for the Ethylene Oxide sterilisation process, is also listed as a Recognised Consensus Standard which would indicated that it is an acceptable method of sterilisation.
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