Editor’s Note: Copesan Services and PCT magazine recently joined forces to publish The PCT Guide to Commercial Pest Management. In the latest excerpt from this popular book, two of the industry’s leading technical directors examine how to perform pest management in clean rooms.
Today’s advanced industrial and medical technology has created a new and challenging environment for pest management — the “clean room.” A clean-room environment can be a room, compartmentalized area, series of rooms, or an entire building.
Clean rooms are characterized by a requirement that the air in them is kept free of contaminants and particulate matter down to an extremely fine level of purity. Dirt, polluted air, microbes, volatile organic compounds (VOCs), shed hair and skin from humans, respiratory droplets, fibers from clothing, and any other foreign particulate must be maintained at an absolute minimum.
Clean rooms may be found in university and institutional research laboratories, medical-device development and manufacturing facilities, aerospace plants, biotechnology firms, and semiconductor-manufacturing locations.
Those wishing to offer pest management services to firms working under clean-room conditions must adapt their practices accordingly and accomplish the job of preventing and controlling pests without doing anything that will compromise the highly restrictive air-quality standards of their clients’ facilities.
PESTS OF CLEAN ROOMS. Clean rooms are protected from the rest of the facility by multiple contrivances, including airlocks, “air showers” that remove particulate contaminants from persons entering them, positive-pressure air-handling systems, elaborate filtration systems that “scrub” incoming air, as well as stringent requirements pertaining to clothing that must be worn, and personal effects allowed to be transported into the room.
You would not expect a clean room to be infested by German cockroaches, nor would you likely find fruit flies breeding in such a place. Rather, pests of clean rooms are those insects that are lucky, or unlucky, enough to stumble upon them and accidentally or purposely find their way in. Pests typically found in clean room situations include:
- Ants (e.g., pavement ants or similar species dwelling beneath the building’s concrete slab and entering by way of expansion cracks).
- Night-flying insects, such as midges, mayflies, and caddisflies.
- Fungus feeders and moisture-related pests, such as springtails, foreign-grain beetles, plaster (Lathridiidae) beetles, and psocids.
- Flies, including cluster flies, as well as smaller species such as fungus gnats.
- Overwintering pests, such as boxelder bugs and Asian ladybird beetles.
Spiders will also be encountered wherever there is food (insect prey), so they also may pose a threat to air quality in a clean room. Sowbugs, millipedes, clover mites, and other landscape pests may find their way into a clean room if they are abundant around the building and any opportunity exists for them to gain access.
The challenge facing PMPs is that invading insects are themselves a threat to the air quality of a clean room, but pest control materials, if left to volatilize or float in the air, can be as bad or even worse. Particles as small as 0.5 microns (0.0005 millimeters) can sabotage the work being done in some clean rooms; one can only imagine the damage an errant droplet of insecticide spray could do.
Various pests can be attracted to a clean room from the outside by lights or air currents leaking out of the supposedly “sealed” spaces. They may be living in suitable conditions directly beneath the sensitive area, or immediately outside the building and find their way inside by random wandering. They may be small enough to have sneaked past the filters that scrub incoming air, or they may be breeding in a damp void area caused by a water leak, bad drainage, improper landscaping, or some other deficiency. Once inside, it isn’t important whether they die of starvation or lack of water, or whether they chose the site for overwintering and live for a time; they cannot be tolerated.
PEST PREVENTION. PMPs pride themselves on their understanding and practice of Integrated Pest Management; pest management in the clean-room environment must be IPM 10 times over. The pest management program you submit to a client with clean-room requirements will consist largely of elements that have nothing to do with the application of pesticides, and you will need a great deal of cooperation from your client. Consider yourself a consultant more than a pesticide applicator in this type of account. Advise your client on the types of conditions that must exist in order for pest-free conditions to prevail in the clean room.
The central principle of clean-room Integrated Pest Management is to start from the facility’s outer surroundings; identify pest-conducive conditions and pest populations that are present; and then, working from outside in — from least-sensitive to most-sensitive — block and thwart a pest’s progress into the clean room.
Facility Surroundings. Most facilities using clean rooms are in reasonably clean, well-landscaped areas, so they don’t receive pest pressure from filthy conditions. Nevertheless, pest-breeding opportunities are bountiful even in the tidiest industrial park. Decorative, scenic ponds (often necessary as a reservoir to hold fire-fighting water) invite mosquitoes and other aquatic insects. Landscaping mulch and thatch from lawn mowing provide ideal conditions for the breeding of moisture pests, such as springtails and plaster beetles. An upwind lake or river can provide thousands of night fliers, a few of which may make their way into a sensitive zone. Even the most pest-proof of all air-filtration systems will let an occasional night flier in if tens of thousands of them are crashing into it all night long. Lights near, on, and in the building serve as beacons to insects that are hard-wired to fly toward light. Standing water in ditches, storm sewers, and puddles on the roof can contribute to the presence of night fliers and moisture-related insects.
Building Exterior. “Pest-proof” is a relative term, and no building can be completely pest-proof. After all, buildings have to breathe. Weep holes in brick facades and window systems are necessary components of a building’s construction. Doors are opened and closed all day — and possibly all night. People and goods come and go, and air currents may suck insects into the building. Attractive landscaping, which is important to good corporate citizenship, contributes other opportunities for pest insects to thrive nearby.
Building Interior. Almost all structures are built on soil and the creatures that live in that earthen environment are not aware that they are unwelcome in the space above their natural habitat; thus, they are bound to spill over into interior spaces from time to time. An ant here and a sowbug there can’t hurt anything in an ordinary office building, but in a clean-room environment it is a different matter. Start from the outside, some distance from the building that houses a clean-room environment, and work inward to identify weak spots that would allow pest access.
Landscaping. Encourage your client to use minimal ornamental landscaping, with a well-drained, 3-foot-wide rock border around the perimeter. Be sure the slope of the terrain leading away from the building is downward, so moisture is not trapped close to the building. Check rain gutters, roof scuppers, and downspouts for clogs or stoppages.
Discourage the use of flowering plants and shrubs in landscaping, as well as any that produce berries or other types of fruit, since these naturally attract insects. Advise your clients against planting low-growing cover such as ivy, juniper, or any shrub that will trap wind-blown debris, since these create a high-moisture, fungus-laden environment directly against the building that will encourage the development of springtails, psocids, plaster beetles, and similar insects. If present, trees should be sparsely planted, and no part of any tree or shrub should contact the building’s walls or roof. Shrubs should be widely spaced and of the “goblet”-shaped variety so that it is easy to rake debris from beneath.
Encourage your client’s grounds crew to bag grass clippings as they mow; this will reduce the amount of thatch that traps moisture and will prevent accumulations of grass clippings from filtering down into the rock-foundation border.
Lighting. Lighting should be kept to a minimum, and any bright lights that must be mounted on the building should be of the sodium-vapor variety, which is much less attractive to night-flying insects than traditional mercury-vapor or incandescent lighting. If mercury-vapor lights have any place at all, it’s in the parking lot, at least 100 feet from the building. This arrangement can attract insects away from the building, instead of toward it. If interior lights are visible at night from the inside, this will attract insects — some of which will find their way inside. Ask your client to consider shading windows in lighted rooms near a clean-room area — or better yet, turn off the lights at night, if possible.
Roof. Check the roof periodically to ensure there is no standing water, clogged drains, or other water or moisture problems. While on the roof, make sure air filters are tightly in place with their edges snugly gasketed against their frames. This will thwart insects that may try to crawl past the filter elements by going around the sides.
Windows. Windows must fit tightly and, if screens are used, they must be rated at least 24-mesh. Even this fine a screen will admit some insects. If the windows have a weep gap, this can be packed with a loose bead of copper mesh to reduce insects’ ability to get into the building.
Trash. Compactors and trash Dumpsters must be isolated from any part of the building that is close to a clean-room area, and must be kept as far from entry doors as possible. Outdoor trash containers around a clean-room facility must be serviced (emptied or changed) at least weekly, and be kept almost clean enough to eat out of. Your client cannot afford to have any flies breeding on site.
Building Construction. Masonry foundations and exterior walls must be free of gaps; masonry blocks used in the construction of foundations and walls should be filled or capped to prevent pests from moving upward within them. Gaps in masonry or between pre-fabricated, tip-up walls must be sealed using an appropriate, flexible sealant. The same applies to gaps where windows and doors are mounted. Any such building used needs to be inspected on a regular basis for gaps, with the gaps then sealed with an appropriate sealant that will move with the building and maintain its integrity.
Interior drywall must extend from slab to slab, be sealed to the floor and extend above the false ceiling to the cement sub-floor above. Penetrations for electrical or other utilities must be sealed, both below and above false ceilings. Especially in clean-room areas, but also throughout the building’s ground floor, expansion joints must be sealed if possible with a flexible sealant. In carpeted rooms, it will be necessary to lift the edge of the carpeting to expose the expansion joint for sealing.
In the clean room itself, whether it consists of one compartment, many rooms, or the whole building, a level of pest imperviousness must be achieved that goes beyond normal construction practices. For example, electrical outlets and switches provide a direct connection to anything behind the wall and beneath the floor. To completely seal off rooms from the voids behind and beneath them, the gap between switch and outlet boxes and the hole that was made in the wall to accommodate them must be sealed with drywall compound, tape, or another sealant. Silicone caulk can then be applied around small holes where wires enter or to seal unused knockouts and drill holes in the switch and outlet boxes. Ceiling exhaust and ventilation fixtures and lighting may have to be dealt with in a similar way, to ensure that there is no opportunity for an insect or other arthropod to find its way into the clean space.
Kitchens, cafeterias, employee dining rooms, locker rooms, and restrooms support many of the pests in a commercial account, given the presence of food, water, and proximity to plumbing and sewage systems. Thus, sanitation and structural maintenance must be perfect in these areas. Drains must be regularly cleaned and free-flowing; tiles must be tightly grouted throughout these areas. All kitchen equipment, including dishwashing machines, sinks, stoves, fryers, etc., must be maintained in a condition that makes any kind of insect breeding nearly impossible.
Trash should be removed from the building at least daily, and Dumpsters should be emptied and washed (or replaced with a clean unit) at least once a week. Trash from offices must be taken to the dumpster at least daily, in tightly tied, durable, plastic bags. Trash cans should be washed and rinsed once each week.
Wastepaper baskets should be used only for dry paper; all other trash goes into designated trash containers. Even one banana peel, orange rind, or apple core can turn a wastepaper basket into a fly-breeding area.
Recycling Areas. If can and bottle recycling is offered, the receptacles must be emptied and thoroughly washed and rinsed at least once a week. Encourage employees to rinse and thoroughly drain cans and bottles prior to placing them in the recycling receptacle. All employee belongings — coats, bags, backpacks, purses, and lunch boxes or bags — must be confined to the locker and dining areas; no food or beverages should be taken outside of these areas.
PEST CONTROL. Insect light traps (ILTs) should be installed indoors in such a way that they are not visible from the outside and they progressively intercept flying insects that manage to get inside in less-sensitive areas before they get close to a clean room. By themselves, ILTs are of limited value, but in a clean-room facility, they are an indispensable part of an integrated strategy.
Recommended places to install ILTs include: in entry vestibules, in loading and shipping docks, in boiler and utility rooms, in the employee cafeteria and locker room, and in hallways leading to clean-room areas. The specific flying-insect pressure in the facility will dictate whether the traps are mounted high or low. Traps intended to catch night fliers can be mounted high (e.g., hung from ceilings or over dock doors), and traps intended to catch house flies and other filth-breeding flies should be mounted close to the floor.
Inspect and thoroughly clean all insect light traps as part of every service visit, and make a record of the kinds of insects present: filth flies, night fliers, small flies such as fruit flies, etc. This may help you pinpoint improvements that the facility staff needs to make in sanitation, maintenance or personnel practices.
Exterior Pesticide Use. Any consideration of pesticide use begins on the outside of the structure and proceeds inward. If you have identified pest pressure from the building’s landscaping and have exhausted all available non-chemical options, you may decide that the facility could benefit from an exterior pesticide application. Exterior treatments can reduce pest pressure on a building, decreasing the number of pests that get inside.
Consider granular-insecticide lawn treatments — watered in immediately after application via rainfall or irrigation—to reduce populations of root weevils, earwigs, ground beetles, and other turf-related pests. Spray treatments timed to the activity periods of clover mites will be useful in preventing these tiny invaders from finding their way into buildings and into the clean rooms housed within.
For insects that approach the building seeking overwintering shelter (e.g., cluster flies, Asian ladybird beetles, boxelder bugs, and paper wasps), consider exterior treatments to the building that are timed to the arrival of these pests in later summer and early fall. Any exterior treatment must be done under the lowest pressure possible, on a day when there is little or no wind, and the spray must be kept away from any potential entry into the building, including air-intake vents, exhaust vents, open windows, or doorways. Make sure that no insecticide — whether granular or liquid — comes in contact with sidewalks, patios, or any place where employee foot traffic might pick up the materials and carry them into the building.
Ants nesting near the building can be eliminated, or their populations reduced, with a direct treatment to their nests with an appropriately labeled spray or bait. Bait stations can be established around the perimeter of the building and maintained as part of the regular service routine.
Insects and mites that are associated with rodents and birds can be kept away from the building by having an effective rodent control program around the perimeter of the building, and ensuring that the building is constructed or modified in such a way that it does not present any opportunities for birds to feed on premises, or to roost or loaf on rooftops, roof parapets, or window ledges. PMPs must consider rodents and birds in the planning phase of designing a pest management program for clean-room facilities.
Interior Pesticide Use. There are some interior areas outside the clean room where pesticides can be of use. Ant control can be accomplished outside of the clean room by placing baits along observed feeding trails. Away from clean rooms, it would be acceptable to place residual insecticides (dust or liquid) directly into cracks or expansion joints leading to probable nest locations. Cockroach baits can be used in kitchen, dining, and locker room areas, as in any other account. Make any application of a liquid-residual insecticide with the lowest pressure possible, and avoid the use of space-treatment materials, including pressurized aerosols, anywhere in a building housing a clean room. If a dust is used, make sure that none is in an exposed area. Dusts may only be used deep in cracks or in voids that cannot lead to any part of a clean room.
Entry into the clean room can involve significant time and preparation. Some clean room entry procedures only involve donning a Tyvek coverall, booties, gloves, and hairnets; others require entry through an airlock and wearing a sterile “moon suit,” plus scrubbing in an air shower prior to entering the room. This involves significant expense (disposable suit, booties, respirator cartridge) and time for each entry cycle. In some cases, the technician might not be authorized to enter the clean room at all.
In facilities that contain clean rooms, crawling insects can be intercepted in the same way as flying insects — by trapping them as they enter less-sensitive areas from outdoors, long before they make their way anywhere near the clean areas. Sticky traps, placed inside durable, low-profile monitoring stations are an excellent way to trap wandering ground beetles, sowbugs, millipedes, earwigs, and other occasional invaders that find their way inside.
Place the traps in secluded areas, near doorways, in shipping and receiving docks — any place it is possible for an insect to crawl into the building; check them on every service visit. Since decaying insect parts contribute to the overall air quality of a building, change the sticky traps and remove the trapped insects from the building each time a trap shows any catch activity.
PESTS IN CLEAN ROOMS. In spite of all the preventive and remedial measures described, insect activity may at some times be noted within the confines of the clean room. If you are faced with this situation, some helpful tips include:
- Ask your facility contact to supply you with a specimen of the pest. Identify the pest, and list what you know about that pest’s biology, behavior, food choices, and breeding conditions. This should tell you where it is likely to have come from, and may give a hint as to how it entered the building and eventually made it into the clean room. For example, springtails found in a clean room can indicate there is a damp condition immediately outside the building, beneath a floor slab, or in a wall void that needs to be corrected. Investigate to find the “reservoir” population (the insects breeding directly in their preferred habitat), and try to eliminate that.
- Determine the likely source of the pest. Is it an aquatic night-flying insect that came from a nearby pond or stream? Is it likely to have been breeding in the lawn or landscaping near the building? Was it attracted to light? Could it have hitchhiked into the clean room on supplies? Springtails in a clean room have been known to originate from a larger population of springtails that were living under the polyethylene sheet that had been laid beneath the rock border around the outside of the building. Once the rock border was removed, the sheeting was picked up, and the soil beneath was treated with insecticide and allowed to dry out. The polyethylene sheeting was replaced with a permeable landscaping fabric, which allowed the soil to dry out properly and prevented any future springtail problems in the clean room. The identity of the pest found in a clean room will almost always point to a similar biological or behavioral feature of the pest that will indicate its likely source — and suggest remedial measures that can be taken, without pesticides needing to be applied in the clean room.
- Take appropriate supplemental non-chemical steps to eliminate the source or the pest’s route of access to the building and the clean room. It may be necessary to modify the exterior landscaping; make improvements in indoor sanitation; find and seal cracks and expansion joints; check and, where necessary, improve the sealing around the clean room itself; investigate and possibly repair the facility’s air-handling and air-filtration system; add sticky traps to intercept insects before they get close to the clean room; or undertake a variety of other non-chemical measures.
- Apply pest control devices or materials, whether sticky traps, insect light traps, or pesticides, only as a last resort and only if this can be done in such a way that there is no chance this activity could add to the particulate load in the clean room’s environment. Some pesticide applications that might be permissible inside a clean room include:
- Use of cockroach gel baits, placed on a retrievable station (bait pucks or small pieces of stiff, non-fibrous paper or Tyvek).
- Use of similarly formatted ant-gel baits or bait stations.
- In very rare instances, application of a liquid or dust insecticide into cracks beneath floor slabs that are sealed immediately afterward, to control sub-slab populations of termites, certain ants, springtails, etc.
- If it is necessary to even consider application of a residual insecticide to an exposed surface, consider applying with a brush (not a sprayer).
In addition to pesticides, it may be permissible to install sticky traps in select locations of a clean room (e.g., in a false ceiling). If this is done, make sure the traps are checked regularly and removed as soon as they have accomplished their purpose.
Clean rooms are one situation where it is wise to rely on the client to deliver remedial pest management service. Since it is difficult to get into clean rooms, consider supplying the client with whatever they need, and instructing them on exactly what to do with it in the clean room. For example, if you want to place a sticky zone monitor into a ceiling void, inform a facility’s technicians as to where the device should be placed and let him or her place it. Prepare ant- or cockroach-bait placements, and tell your contact where they should be placed or from what location they are to be removed. This can save time and help to preserve the clean room’s air purity. In this instance, you are their valued consultant, and they implement your instructions.
SUMMARY. Considering the highly restrictive nature of clean rooms pertaining to personnel entry, and considering the absolute zero tolerance both for pests and pest control materials, PMPs should focus their efforts on preventing pests from getting into clean rooms in the first place.
PMPs must act as consultants for their clients, advising them on sanitation, design, construction, and maintenance improvements that can be made in the building’s surroundings, on the building itself, and inside the building to make the whole area as unfriendly to pests and as impervious to pest invasion as possible.
When it is necessary to apply a pest control device or, in rare cases, a pesticide, inside the clean-room environment, it must be done using materials and methods that reliably preclude the possibility that any contaminants will be added to the particulate load of the air in the clean room.