Response to Low ppm Readings on a Hydrogen Peroxide Monitor

Many users are concerned about exposure to hydrogen peroxide vapor from their sterilizers and so have invested in continuous monitors for hydrogen peroxide. These monitors provide a real time reading of the hydrogen peroxide concentration in ppm but now the user needs to interpret these numbers and respond appropriately.

If there is a large leak of hydrogen peroxide vapor and the hydrogen peroxide monitor is in high alarm, the response is simple – clear everyone out of the immediate area until the ventilation reduces the concentration to safe levels (as determined by the monitor). Fortunately massive leaks rarely occur, but it is not uncommon for people to see low ppm readings on their hydrogen peroxide monitors. The question then arises as to what constitutes over exposure to hydrogen peroxide vapor and what actions should be taken.

Some people rely only on the OSHA permissible exposure limit (1 ppm, calculated as a time weighted average (TWA) over 8 hours). The argument goes that so long as the OSHA PEL is not exceeded all is good in the world of hydrogen peroxide exposure. Sometimes this calculation is tempered by saying that the hydrogen peroxide exposure should not go over the NIOSH IDLH (75 ppm for hydrogen peroxide).

Following this logic, it would be OK for someone to be exposed to 50 ppm hydrogen peroxide continuously so long as it does not exceed the PEL, i.e. < 480 minutes/50 ppm = < 9.6 minutes, and 25 ppm for < 19.2 minutes etc. are OK. I would not want to be the person exposed and certainly not on a regular basis. These numbers may seem high but we have seen hydrogen peroxide vapor in the 30 to 40 ppm range being emitted from one model of hydrogen peroxide sterilizer whenever the door was opened after completion of a cycle. Hydrogen peroxide has essentially no odor and so apart from some a monitor or other method to detect hydrogen peroxide there is no way to know if hydrogen peroxide vapor is present.

Probably the most respected industrial hygiene organization in the world is the ACGIH and the ACGIH has issued a threshold limit value for hydrogen peroxide of 1 ppm calculated as an 8 hour TWA. The similarity with the OSHA PEL is not coincidental since the OSHA PELs were initially derived from the ACGIH TLVs in 1972 and neither the ACGIH TLV nor OSHA PEL have revised the exposure limit for hydrogen peroxide since then.

For compounds with no short term exposure limits the ACGIH recommends the following: Excursions in worker exposure levels may exceed 3 times the TLV-TWA for no more than a total of 30 minutes during a work day, and under no circumstances should they exceed 5 times the TLV-TWA, provided the TLV-TWA is not exceeded. [2008 TLVs and BEIs based on the Documentation of the threshold Limit Values for Chemical Substances and Physical Agents and Biological Exposure Indices, p 5.]

Applying this guidance to hydrogen peroxide, worker exposure may exceed 3 ppm for no more than 30 minutes during the work day and under no circumstances should they exceed 5 ppm. These levels are thus similar to a short term exposure limit (STEL) and ceiling limit respectively and are consistent with the STELs for hydrogen peroxide promulgated by several governmental occupational safety agencies. Washington state for example has a STEL of 3 ppm (15 min TWA) and the United Kingdom and some other European countries have a 2 ppm STEL. [Ref EH40, 2005]. While there is no OSHA STEL for hydrogen peroxide, this ACGIH guidance represents best practice when using hydrogen peroxide.

If the monitor always reads less than 1 ppm then the user need have no immediate concerns about exposure to hydrogen peroxide, the 8 hour TWA will be less than the OSHA PEL. However, we have found on many occasions that the readings often start our small but over time they increase. Thus if the readings increase over successive cycles of the sterilizer and become significantly higher than previously seen, even if still within safe limits, then these numbers can serve as an indicator that the sterilizer should be serviced soon.

If the readings occasionally rise between 1 to 5 ppm, as may some times occur when the sterilizer door is opened, then the user should step away from sterilizer and return once the readings have fallen to safe levels (< 1 ppm). If this ‘puff’ of hydrogen peroxide is new to the operation of the sterilizer, then again, it is time for maintenance.

If the hydrogen peroxide monitor goes above 5 ppm, then this concentration poses a potential hazard to employees and the problem should be rectified and the sterilizer manufacturer should be asked to correct the problem. If the manufacturer says that the sterilizer or other equipment is operating normally, then other measures such as engineering controls, modified work practices etc. should be employed to ensure workers are not exposed to hydrogen peroxide above 5 ppm.