Keeping a lid on biohazards
by Hank Hogan
“Keep them in. Those you can`t keep in, destroy. Those you can`t destroy, minimize.”
This capsule description of biocontainment practices and decontamination procedures is provided by Dr. Robert W. Powitz, principal consultant at R.W. Powitz and Associates (Old Saybrook, CT). The official version is spelled out in the U.S. government publication “Biosafety in Microbiological and Biomedical Laboratories,” 3rd edition, 1993, HHS Publication No. (CDC) 93-8395. The publication lists Biosafety Levels 1 to 4, with Level 1 designated as virtually harmless conditions, while Level 4 is reserved for exotic, life-threatening agents such as Ebola, Lassa and Marburg. In both short and long versions, one factor remains constant, however. As the danger level increases, facilities and personnel must meet increasingly stringent biohazard containment and biodecontamination requirements.
The development of HEPA and ULPA filters for the semiconductor and other industries has in turn been a boon for biohazard containment. There are differences, however, in the application of filtration technology to biocontainment. In addition to the fact that biomedical facilities operate at negative pressure relative to the outside air, as described by Dr. Robert McKinney, director of the division of safety at the National Institutes of Health (NIH) in Rockville, MD, “in the semiconductor industry, they`re looking for total particles, whereas with biodecontamination you`re only looking at a subset of what might be in the air. Nonetheless, HEPA filtration is one way to reduce bio-burden.”
The United States Army Medical Research Institute of Infectious Diseases (USAMRIID) in Fort Detrick, MD, maintains Biosafety Level 3 and 4 facilities with laboratories ranging in size from 2,600 to 26,000 square feet. With 10 to 12 air changes an hour, they are roughly equivalent to a Class 10 cleanroom.
At Biosafety Level 3, all exhaust air is HEPA-filtered. The incoming air is not filtered as stringently since exposure to the outside world is relatively harmless compared to the lab itself. At Biosafety Level 4, however, not only is the exhaust air run through two HEPA filters in series, but the air intake supply is HEPA-filtered as well. As explained by Dr. Robert J. Hawley, chief of the Safety and Radiation Protection Office at USAMRIID, “with HEPA filtration on both intake and exhaust paths, even in the event of a power loss or other major systems failure, there is no possibility of microbial migration from the lab.”
Another technique that can be used to decrease airborne bio-burden is high-intensity ultraviolet light, which can kill microorganisms without adverse environmental impact. This approach is being used in some healthcare facilities, particularly to combat tuberculosis. In general, this is done in cases where the ventilation system won`t support a 100-percent air exchange or HEPA filtration isn`t possible. Though less effective than the other alternatives, simple dilution where eight to 10 complete air changes are done an hour can also be tried.
Biodecontamination
In high-level biohazard facilities, air filtration alone is not adequate precaution. If dangerous organisms have escaped their primary containment and contaminated a larger area, biodecontamination may be necessary. One such method, with roots in surgical sterilization, is the use of a mist of formaldehyde gas and water. The water vapor tends to trap any microorganisms while the formaldehyde kills them.
One drawback with the use of formaldehyde, however, is that it is a potential carcinogen, posing both a health threat to personnel as well as restrictions in cleaning up and disposing of the chemical. In a cleanroom, any agent that leaves behind a residue is, of course, automatically a problem.
In response to such concerns, research is underway to find other techniques that do not leave behind a residue and are more environmentally friendly. “The most promising are those technologies that leave no residue, and if they`re chemical, that would be something like hydrogen peroxide or ozone,” comments Powitz.
Unfortunately, hydrogen peroxide vapor is not effective in all situations. One reason is that it doesn`t penetrate as well as formaldehyde, and consequently some cracks and crevices may not be fully disinfected. Hydrogen peroxide is also not compatible with some common materials used in biological labs, such as rubber. Material incompatibility is also a problem with the use of ozone. Researchers believe some combination of chemical disinfection together with ultraviolet light may eventually prove to be the best answer.
Practice makes perfect
Proper personnel control is a key area for biodecontamination. This includes policies and procedures covering the handling of infectious agents and what to do in the event of an incident. “The most important contribution to personnel controls, however, would be emphasis on the importance of training — specifically, interactive training programs,” says USAMRIID`s Hawley.
Interactive training programs can include videos or computer simulations that allow role-playing and what-if scenarios. Training programs begin with work on less deadly or more readily treated organisms. These live simulations provide the hands-on experience needed to achieve the required level of expertise. Once the necessary skill is acquired, along with a working knowledge of policies and procedures, then the worker can move into higher Biosafety level areas.
Inside a high-level Biosafety area, protective clothing not only shields workers from infectious agents, but also keeps any of the everyday microorganisms of the outside world from contaminating the lab. The same is true for all other equipment and materials entering the work areas, including water, which may or may not be sterilized. Whether or not this is done depends on the facility and the organisms being studied.
Cleaning up
The final phase of biodecontamination is the handling of the waste stream. While filtration removes dangerous organisms from the air, a number of other neutralization methods are used for solid and liquid waste. One method is steam sterilization through variations of autoclaving. Another is the use of sodium hypochloride (bleach), but since this chemical is corrosive and not environmentally friendly, other decontaminates such as hydrogen peroxide and UV light are also being investigated. As a further precaution, sometimes the wastewater generated from the cleaning process itself is also sterilized.
Animal research
In general, all of the same Biosafety rules and concerns apply to animal research facilities as those working on human health issues, although there are some significant twists. Although infectious organisms that attack livestock may or may not pose a threat to humans, they do present a danger to other, non-infected livestock, and although there are currently no Biosafety Level 4 operations, the safety standards for Biosafety Level 3 in animal disease research are in fact more rigid than Level 3 for research on human diseases.
According to Manuel S. Barbeito, a biological safety consultant and former bio-safety officer for the Agricultural Research Service at the U.S. Department of Agriculture, “the requirements are more stringent than a conventional Biosafety Level 3 facility, because unlike a box containing small research animals that you can seal up and put on a shelf, here the entire room is the box and we have to make sure it`s fully tightened up.”
One problem faced by animal disease research facilities is what to do with the animal remains themselves. So far, the method of choice has been incineration, which is effective but leads to environmental impact issues since the residue literally goes up the chimney. Another approach is dehydration rendering, which removes all water from the carcass prior to disposal. Although it has been in use in facilities in the Netherlands and Switzerland, the procedure is just now being introduced to North America. The Canadian Federal Laboratories in Winnipeg, Manitoba, are implementing the process with some changes of their own.
As described by Lee Thompson, chief of safety and environmental services at the Federal Laboratories for Health Canada and the Canadian Food Inspection Agency in Winnipeg, Manitoba, “the initial phase of the rendering process is in fact a sterilization cycle where we have the capability of autoclaving, steam sterilizing waste before we start the dehydration process.”
After a 121-degree centigrade autoclave for an hour, the dehydration process begins. This runs for 4.5 to 5 hours leaving only the animal`s oils and solids upon completion. These are disposed of in a landfill. The rendering machine is contained so that in the event of a power outage no material escapes. It`s also possible to make repairs and start the process over without opening the chamber. As a result the equipment can safely recover from many equipment and system failures. Thompson reports extensive bio-validation has shown the technique to be effective at removing infectious agents. The same system is also being used to treat the animal effluent waste stream.
Although the system is designed to dispose of only 10 to 15 full loads a year and cannot handle mass production, this is not currently a problem since the nature of the research being conducted does not result in a large number of carcasses.
Only in the movies
Fortunately, despite their deadly and infectious nature, many of the Biosafety Level 3 and 4 organisms actually have a difficult time surviving in the outside world. Changes in temperature and humidity contribute to their mortality. The greatest danger is still to those people actually working with the microorganisms inside the lab. With treatment of the waste stream, there is very little danger of any problems outside the facility itself. As noted by McKinney, “the risk realistically is as great if not greater in the movie theater to becoming infected than it is to be standing outside a laboratory building that is working on tuberculosis. A seat in a theater may have active tuberculosis.”
Hank Hogan is a freelance writer based in Austin, TX. He has written for New Scientist, High Technology Careers, Electronic Components and Multichannel News International. Prior to laying hands on a keyboard, he was a semiconductor process engineer and holds a process technology patent.
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A worker in a biosafety-level area at the United States Army Medical Research Institute of Infectious Diseases in Fort Detrick, MD. Photo courtesy of USAMRIID.