Researchers and staff who will be using, operating, and maintaining the facility should be included in the planning process. IBC members and regulators from USDA/APHIS and state Agriculture Departments should be notified and updated regularly and may also be invited to join the design team. A commissioning agent with experience in testing greenhouse systems would also be a useful team member, though such services would be most valuable at the conclusion of the project. Consultation with users and managers at other research greenhouses is valuable when designing new facilities. The Association of Education and Research Greenhouse Curators²¹ offers an electronic mail forum, web pages, and annual meetings from which detailed information can be gathered.

CONSTRUCTION OVERVIEW

Framing Materials

Typical construction styles for research include even-span with a standard peak, Venlo, and ridge and furrow with gutter connects. Roof styles include the standard peaked, as well as arched, mansard, and Quonset-style. Figure 14 shows examples of greenhouse exterior structures. A headhouse and hallways that are immediately contiguous to the greenhouse are considered part of the containment area.

Figure 14. Greenhouse roof styles
(Reprinted with permission of Hanan, Joe J., 1998. GREENHOUSES: Advanced Technology for Protected Horticulture, CRC Press LLC: Boca Raton, FL.)

Modern greenhouse structures are framed with aluminum (Fig. 15) or galvanized steel; however, many older facilities are framed in wood or metal pipe.

Figure 15. Aluminum-framing under construction

Wood and pipe framing are still being used in new construction of some plastic film greenhouses. A reinforced, rigid frame is preferred for BL3-P and required for BL4-P. The latter requires additional strength and rigidity to accommodate the weight of double-paned, break-resistant, sealed glass.

Use of aluminum or galvanized steel truss framing allows a prefabricated frame to be quickly erected. The rigid frame, coupled with purlins, glazing bars, and other framing members, creates a quality, longlasting structure that can be covered with various glazing materials. Environmental control and containment is enhanced through proper installation and fitting of all materials. Information on structural materials, as well as other relevant topics, can be found in the Book of Standards authored by The National Greenhouse Manufacturers Association²² or in the American Society of Agricultural Engineers Standards 2000²³.

Entry doors and locks

The choice of greenhouse doors should receive careful consideration since containment and security breaches occur most often at points of entry. Specifications for BL3-P and BL4-P facilities stipulate a double set of self-closing and locking doors. High containment facilities also require one-way emergency exit doors for personnel safety.

Traditional cylinder locks offer good security as long as good key control is implemented. Newer electronic systems such as a card swipe or Marlock® keying provide highly restricted access and a log of all entries and exits. Special keys or cards are programmed to allow individuals access to selected areas with one tool. Using this system, fewer keys are issued, key loss is minimized, and codes can be changed quickly and easily.

A double-door entry system, with a dark vestibule sandwiched between the doors, aids in effective insect containment. UV lights may be installed in the vestibule. Air curtains that fan individuals exiting a contained area can help blow organisms and propagules back into containment.

Benching

Many different types of benching can be found in research facilities, but when building a new high level containment greenhouse, the design and materials should be chosen so as to comply with BL-3P and BL-4P requirements. Benches must be thoroughly cleaned and disinfected in conjunction with transgenic research at higher biosafety levels. Those made of aluminum or galvanized steel provide the longest wear, are easiest to clean, and amenable to installing systems for runoff water collection and treatment. An ebb and flow (also called ebb and flood) bench is one that can collect water and recycle it to the bench (see Fig. 11). This system can also be adapted to collect and hold water prior to subsequent decontamination by chemicals or heat.

Ventilation, Heating, and Cooling

Few conventional research greenhouses are built with sealed glazing, mechanically conditioned air, differentially controlled air pressure, and exhaust air filtered through high efficiency particulate air (HEPA filters). Thus new construction is usually needed to meet the standards for BL3-P and BL4-P facilities. Air conditioning is not strictly mandatory for higherlevel containment greenhouses; however the loss of cooling efficiency due to required air-handling measures makes it a necessity in most climates.

The exhaust air produced from negative pressure systems must be filtered to prevent contained organisms from exiting. Intake air is also filtered to prevent introduction of organisms from the environment into the enclosed space. Filter systems can be designed to trap pollen, spores, and other very small particles. High efficiency particulate air (HEPA) filters can remove 0.3 micron and larger particles but still allow gases to transfer across the filter media.

It is relatively difficult and expensive to equip an entire greenhouse to restrict small particle movement. Air-conditioned greenhouses, growth chambers, growth rooms, or biological safety cabinets are alternatives to standard research greenhouses with air filtration systems. Specialists should be consulted when designing or retrofitting facilities that require a highly effective air filtration system. The engineering specifications required for air balancing, ventilating, and cooling BL3-P and BL4-P greenhouses are beyond the scope of this Guide. If this type of facility is required, it is highly recommended to involve an experienced design firm for the project.

Floors and drains

Solid concrete flooring and drains are preferred for new research greenhouses. Commercial greenhouses often use porous concrete floors to allow passage of water. However, BL3-P and BL4-P facilities must have non-porous floors that can be disinfected as well as a system to collect all runoff. The floor of a BL4-P facility must be part of an "internal shell" system that includes the walls and ceiling. Runoff is drained to a decontamination tank or treatment facility before entering a standard sewer or other disposal system. Additionally, sewer vents on BL4-P greenhouses must be HEPA filtered.

Control Systems

Normal building controls cannot readily be adapted to meet the rigorous needs of a high-level containment greenhouse; therefore dedicated controls available from greenhouse control vendors are recommended. New facilities should have control systems that incorporate the latest digital technology, and allow precise environmental control, logging, sensing, alarm, and related functions. Moreover, the security and redundancy functions that are required at higher containment levels prescribe newer digital controls and should interface with the institutional building security system.

Greenhouse managers and others involved in retrofitting existing greenhouses or building new facilities can draw on the experience of USDA officials, the NIH Office of Biotechnology Activities, architects, vendors, and professional colleagues. A partial list of these is included in Appendix II.

²¹ http://www.life.uiuc.edu/aergc

²² Book of Standards. 1995. National Greenhouse Manufacturers Association (NGMA). (Revised 1999) http://www.ngma.com

²³ American Society of Agricultural Engineers Standards 2000. American Society of Agricultural Engineers (ASAE). http://www.asae.org