The most notable amendment is the addition of “Appendix D,” written by the U.S. Department of Agriculture (USDA), which establishes “BSL3-Ag” as a distinct classification of laboratory.

According to the introduction of Appendix D: “Risk assessment and management guidelines for agriculture differ from human public health standards. Risk management for agriculture research is based on the potential economic impact of animal and plant morbidity and mortality, and the trade implications of disease. Agricultural guidelines take this difference into account. Worker protection is important but great emphasis is placed on reducing the risk of agent escape into the environment. This Appendix describes the facility parameters and work practices of what has come to be known as BSL3-Ag. BSL3-Ag is unique to agriculture because of the necessity to protect the environment from an economic, high risk pathogen in a situation where studies are conducted employing large agricultural animals or other similar situations in which the facility barriers now serve as primary containment.

“Therefore, when manipulating high consequence livestock pathogens in the laboratory or small animal facility, facility design and work procedures must meet the requirements of BSL-3 or ABSL-3 with additional enhancements unique to agriculture.”

It also addresses the use of primary containment devices such as biosafety cabinets.

The document makes it clear that the Appendix “provides guidance and is not regulatory nor is it meant to describe policy.” It was necessary because there was nothing in the previous BMBL or USDA guidelines that addressed small-animal facilities or work done with high risk agricultural pathogens in a biosafety cabinet, says Chris Kiley, biocontainment mechanical engineer at Merrick & Company in Atlanta, Ga.

“The USDA guidelines only really addressed large-animal facilities,” he says. “The whole biosafety cabinet part is new.”

The Fifth Edition also addresses for the first time the issue of regularly testing HEPA filters in BSL-3 labs.

The National Sanitation Foundation requires annual testing of HEPA filters within biosafety cabinets, but there was nothing addressing HEPA filters that service entire labs. The new regulation requires scan testing of the filters, as well as pressure decay testing of the ductwork between the room and the HEPA filter in large-animal facilities where the facility barrier serves as primary containment.

Pressure decay testing determines the leak tightness of the exhaust ductwork between the HEPA filter housing and the space. This might make it impossible to install HEPA filters in a “ganged” arrangement in a BSL-3-Ag lab, because the terminal devices are not typically airtight. (In a ganged arrangement, a group of HEPA filter units serving a number of labs are installed adjacent to each other rather than separately above each lab.)

L.W.