Simple Human Error Leads to Ethylene Oxide Release from Sterilizer

We received a call this morning that there had been an ethylene oxide release from a hospital sterilizer. Sterile processing staff at a large hospital placed a load into one of their three ethylene oxide sterilizers and started the cycle. A short while later the cycle aborted and while trying to identify the problem, one of the staff members unexpectedly opened the door.

The ChemDAQ ethylene oxide monitors immediately went into alarm and the two employees rapidly left the room. They and the rest of sterile processing evacuated the department until the monitors showed it was safe for them to return. In addition to the two women in the sterilization room, the other four workers in the department were all sent to the emergency room for evaluation. Fortunately, it appears that everyone was able to get out quickly enough that no-one suffered adverse symptoms from exposure to ethylene oxide.

The cause of the problem was later found to have been due to a simple human error. The manufacturer's service technician had been on-site earlier that day to do the regular preventative maintenance and when he was finished, he forgot to switch the sterilizer back from service mode to normal mode. In service mode the cycles times are short and the door locks are apparently disabled.

This incident shows the importance of being aware that even well designed, well maintained equipment can and sometimes does fail because of a simple human error that any of us could have made.

This blog has railed against the use of badges for ethylene oxide monitoring in healthcare as being ineffective. If these two workers had not evacuated after the sterilizer door was opened, then their exposure to ethylene oxide would have been considerably higher and it would have made no difference whether they were wearing a badge or not. Fortunately for the staff at this hospital, they were protected by a ChemDAQ monitoring system.

Exposure Limits for Peracetic Acid

As a manufacturer of gas monitors, one of the questions that we face is where to set the alarm limits. The ChemDAQ Steri-Trac^® monitor has two instantaneous alarms (high and low) which respond to the current concentration of the target gas and the ChemDAQ DAQ^® computer, in addition to data collection, reports etc., calculates time weighted averages and provides alarms based on these time weighted average exposure (TWA).

For a vapor such as hydrogen peroxide, which has an OSHA permissible exposure limit (PEL) of 1 ppm (8 hr TWA), the DAQ has an 8 hour TWA of 1 ppm. There is no OSHA short term exposure limit for hydrogen peroxide and so the DAQ does not have a STEL alarm.

For vapors such as peracetic acid for which there are no OSHA PELs, alternative exposure limits must be sought. The first step is look to see if there are any ACGIH threshold limit values (TLV) or other recognized exposure standard. The ACGIH does not have a TLV for peracetic acid, but it has proposed a short term exposure limit (STEL) of 0.4 ppm. In the absence of recognized exposure limits, one looks for published studies and reviews of published studies.

Recently Pechacek, Maier and Haber reviewed a range of studies of the health effects of exposure to peracetic acid and came up with several recommendations. The authors are with Ecolab, one of the largest suppliers of peracetic acid and TERA, a non-profit organization dedicated to solving problems associated with public health.

The authors' first recommendation is that neither a ceiling limit nor a STEL on its own is appropriate since

" PAA is an irritant that can cause cytotoxicity. Insufficient dose-response information is available to ensure that the absence of a sensory response also protects from accumulating subclinical cytotoxic responses." The authors go on to comment that the combination of 8 hr TWA and STEL is valuable. This conclusion may have significance to the ACGIH proposed STEL for peracetic acid.

In addition to recommending the use of both an 8 hr TWA and STEL, Pechacek et al calculated a value for the 8 hr TWA occupational exposure limit based on published reports of 0.26 to 1.56 mg/m3, which corresponds to a concentration range of 0.08 to 0.5 ppm.

The ChemDAQ DAQ calculates both the STEL and the 8 hour TWA, and the ChemDAQ alarm limits are set at 0.4 and 0.2 ppm respectively, both within the range recommended by Pechacek, Maier and Haber.

Honeywell Stops Taking Orders for Oxyfume Ethylene Oxide Sterilants

Honeywell announced in August 2012 that it would discontinue production of the Oxyfume ethylene oxide (EtO) sterilant gas cylinders because of Clean Air Act regulations from the EPA banning the sales and use of most HCFC based products like Oxyfume in the end of 2014.

On March 15th, Honeywell announced that they would no longer receive orders for Oxyfume after March 31st 2013 and that Oxyfume 2002 and Oxyfume 2000 cylinders should be sent to Honeywell for recycling until production ceases later this year. Cylinders of Oxyfume 12, a CFC-based product phased out in 1995, cannot be received by Honeywell and current and former customers should contact Honeywell for information on how to handle these cylinders.

Ethylene oxide used to be the dominant low temperature sterilant in healthcare and ethylene oxide blends were the primary means of delivering EtO. The blends were used because ethylene oxide is a flammable/explosive gas with a lower explosive limit of 3% v/v with mixtures being explosive up to 100%. Ethylene oxide explosions can cause major damage, as happened to Sterigenics in 2004; and so the ethylene oxide is diluted with an inert gas to make the mixture non flammable. Both carbon dioxide and chloroflorocarbons (CFCs) were used as the inert gas. Honeywell's Oxyfume 12 contained 12% EtO and 88% CFC-12, (Dichlorodifluoromethane) which was banned under the Montreal Protocol, its manufacture was banned in the United States along with many other countries in 1996 due to concerns about damage to the ozone layer.

CFCs were replaced with hydrochloroflurocarbons (HCFCs) and Honeywell introduced the oxyfume 2000 which contained 8.6% EtO in 91.4% HCFC-124 (Chlorotetrafluoroethane) and the Oxyfume 2002 which contained 10% EtO, 27% HCFC-22 (Chlorodifluoromethane) and 63% HCFC-124. The switch to the HCFCs was a temporary measure and they in turn are being phased out under the revised Montreal Agreement.

Market forces are also acting against the EtO blends which held a dominant market position before the 1990s. Honeywell estimates that more than 70 percent of hospitals in the United States have used Oxyfume in their sterilization facilities over the last 40 years. In 1993 Advanced Sterilization Products (ASP) launched its Sterrad hydrogen peroxide sterilizer which offered much shorter cycle times compared to the ~ 15 hours required for EtO sterilization and aeration and ASP's marketing emphasized the carcinogenic properties of EtO (even though the OSHA permissible exposure limits for EtO and hydrogen peroxide vapor are the same 1 ppm time weighted average over 8 hours).

The Sterrad system offered significant safety features, particularly by operating under reduced pressure (leaks will be in not out) and newer EtO sterilizers were introduced by 3M and Steris Corporation that also operated at reduced pressure and used single use cartridges. Both of these measures served to reduce employee exposure to EtO compared to the older pressurized systems. The single use cartridges uses a small quantity (100 - 170g) of 100% EtO and so do not use the HCFC blends and avoid the need to run gas lines and change EtO gas cylinders.

There has been a lot of confusion over the years about whether EtO was being phased out. It is not! It is the CFC and HCFC blend gases that are being phased our to protect the stratospheric ozone layer. EtO is still the major gas sterilant used by medical device manufacturers because it can be used for sterilization of almost all medical devices including plastic and heat sensitive materials.

EtO is not going away; the world production of EtO was 19 million tonnes in 2008 and 18 million tonnes in 2007 which places EtO as the 14th most produced organic chemical; and the amount of EtO used for sterilization is a minuscule fraction of this production. Even though EtO use in healthcare has dropped in the last two decades, there are still many hospitals that use EtO as for low temperature sterilization and it is likely that EtO will continue to be an important low temperature sterilant gas for the foreseeable future.