In the July 2012 issue of Lab Manager, we wrote about hydrogen peroxide vapor systems and basic safety concerns with using this chemical for decontamination. The proliferation of research facilities, particularly healthcare, life sciences and animal care centers, points out the need for environments that are sterile in terms of unwanted diseases and vectors.
We have recognized a trend toward using the HPV systems for large-scale decontamination. VHP Safety Basics, our initial article, addressed basic operation cycles of hydrogen peroxide vapor systems and discussed the hazards associated with their use, including symptoms of exposure and basic safety precautions. We opened the article with a fictional scenario of an over-exposed technician. This scenario and the article drew the attention of one manufacturer of HPV decontamination systems.1 Based on the excellent feedback, we decided to issue a second article clarifying a couple of points and providing more discussion and detail on HPV system safety protocols.
Let’s start at the beginning. The hydrogen peroxide used in HPV systems is much more concentrated than is the common drugstore product purchased over the counter. Typically, commercially available 30 to 35 percent concentration (w/w) hydrogen peroxide solution is flash evaporated by the HPV equipment and distributed into the area targeted for decontamination. Recommended personal protective equipment (PPE) will depend on whether you are handling the liquid concentrated source chemical, preparing to run the HPV system, or readying the area for re-entry. Follow the manufacturer’s recommendations or the safety data sheet for the specific material you are dealing with.2 In general, handling the concentrated liquid chemical will require specific PPE, to protect against potential splashes, skin contact and inhalation, while re-entering a decontaminated room that has been properly purged might require only standard lab wear such as a lab coat and eye protection. If you have questions, ask to review the safety data sheets, speak with a supervisor or safety professional, and follow the specific safety protocols provided by the manufacturer.
If you will be handling the concentrated form or working in an area recently decontaminated, it is important to know the symptoms of exposure.3 We mentioned in the first article that hydrogen peroxide is irritating, especially to the mucous membranes of the eyes, nose, throat and pulmonary system. This is what industrial hygienists refer to as warning properties of the chemical or agent. In other words, we can perceive the exposure occurring with our senses. The trouble with hydrogen peroxide is that this “detectable” threshold may vary from person to person, and the personal exposure limit (PEL)—the limit to which a worker can be exposed on average during working hours—as specified by OSHA, is a very low one part per million (1ppm) calculated as an eight-hour time-weighted average (TWA). The bottom line is that if you don’t have a hydrogen peroxide sensor, and if your nose is tingling or your eyes or throat are feeling funny, something is not right and you should leave the area and investigate further.
And this leads us to our exposure scenario. As we have already stated, the opening scenario of our original article was fictional, but let’s look a little closer at what can go wrong and the safety precautions that can minimize or eliminate possible exposures and subsequent injuries. As a quick review, there are four phases of decontamination using HPV systems: preconditioning, gassing, dwell period and aeration. The initial phase, preconditioning, does not present an exposure hazard, as no hydrogen peroxide has been introduced. The second phase, gassing, presents the most potential for danger, as this is when the hydrogen peroxide is rapidly distributed to build to the target level for effective decontamination. The third phase, dwell period, does just that: The concentration level of the hydrogen peroxide gas is maintained (it “dwells”) during the required or recommended contact time—thus, exposure is possible. The final phase, aeration, removes the hydrogen peroxide vapor from the enclosure or area to safe working levels, and exposure concerns gradually decrease to the end of this phase.
So, how could an employee become exposed to hydrogen peroxide using HPV systems? And what do we do to prevent this from happening? As we mentioned in the first article, HPV decontamination systems have been in use for more than 10 years. Manufacturers have developed and refined safe operating protocols over the years. Most offer on-site, multi-day training on proper setup, operation and safeguards. First and foremost, an employee, in order to become exposed, would have to ignore the safety protocols and/or breach the containment area. This should never happen. Unfortunately, no matter how thorough the safety procedures and training or how foolproof the system, we see employees disregard or defeat them too often. Sometimes it is out of ignorance—perhaps a new employee or one from a different department was unaware of the process. Other times it might be a hardworking, conscientious employee pressured with a deadline or shortcutting to get more done in a day.
The only other potential for employee exposure would be a malfunctioning system, such as a leak or a faulty reading from a sensor. HPV systems usually incorporate sensors to monitor the levels of hydrogen peroxide during the conditioning and maintenance phases and to indicate the end of the purge cycle. In addition, there are personal monitors and instruments that must be used to check areas prior to re-entry or use.
So, how do we prevent exposures from occurring? Looking at the first situation, we want to ensure that all employees who will operate the HPV system receive the recommended training from the manufacturer. Then provide awareness training (to the appropriate level of detail) for employees that may work in the enclosure(s) or area(s) under decontamination. Finally, make sure the area is secured, well marked or otherwise clearly designated as a “No Entry” area until decontamination is complete and the purge verified. For the second scenario, potentially malfunctioning equipment, the operators must thoroughly inspect the equipment before use. Check seals, sensors and controls according to manufacturer’s instructions. Know how to calibrate and operate the monitoring equipment and have spare sensors on hand. Most important, make sure the monitors are used for each decontamination project and that areas or enclosures are cleared before re-entry or use.
In summary, HPV systems have many advantages over systems that use other agents, especially for large rooms or areas. Hydrogen peroxide is a very effective decontamination agent. Manufacturers have spent more than 10 years developing the technology and refining safe operating procedures. Safe use of HPV systems is a matter of training employees in following the manufacturer’s procedures and proper use of available monitoring sensors. Knowledge of the HPV cycle and understanding the application equipment and the monitoring instruments can prevent unwanted employee exposures and possible injuries.
1. Bioquell, Bioquell, Inc., Horsham, PA. 2014 http://www.bioquell.com/us/
2. Vaprox 59 Hydrogen Peroxide Sterilant, Steris Corp., St. Louis, MO. January 2013. http://www.steris.com/documents.cfm?id=A127
3. Hydrogen Peroxide, US Department of Labor, Occupational Safety and Health Administration. Washington, D.C. 1996 https://www.osha.gov/dts/chemicalsampling/data/CH_246600.html