96 
occurred because the workers, mainly in diagnostic laboratories, were 
unaware of the virus in their samples. 
2 . Impact on the Environmental Spread of Possibly Hazardous 
Agents 
The NIH Guidelines are directly concerned with preventing the 
release of cells and microorganisms containing recombinant DNA 
molecules, or the release of such molecules themselves, into the 
environment, thus preventing potential exposures of humans, other 
animals, and plant communities. 
The Guidelines require decontamination of all liquid and solid 
wastes generated by low-, moderate-, or high-risk experiments. As 
the assessed risk of these materials increases (low — > high), further 
measures are required to increase the certainty of containment. The 
Guidelines recommend the decontamination of no- or minimal -risk 
materials before their disposal to the environment. This is a standard 
microbiological practice. 
The Guidelines prohibit the release of contaminated air under 
ordinary conditions. Procedures involving low- and moderate -risk 
materials that may produce aerosols are confined to primary barriers. 
Contaminants in the exhaust air from these barriers are removed by 
filtration. 
The potential for accidental release of recombinant DNA materials 
into the atmosphere, however, increases with decreasing containment 
requirements (moderate — ) minimal). Harmful secondary effects from 
such accidental release of minimal-, low-, or moderate-risk materials 
are exceedingly remote. An analysis of 36 reported laboratory-acquired 
micro -epidemics in the period l§25-lU T J'5 - mvolving over 1,000 infections 
with human etioToglc "agents of classes 2, 3, and 4 ~demonstrated no 
infections among persons who" we re neverTn the laboratory building 
or who were not associated in some way with the laboratory (2). Almost 
all of these outbreaks occurred in the absence of genuine efforts to 
control contaminated air, liquid wastes, refuse, and laundry. 
Adherence to the NIH Guidelines should prevent any potential 
release of high-risk materials to the environment. All high-risk 
materials are required to be isolated in physically contained, absolute 
primary barriers. All effluents from these barriers are sterilized. 
The barriers themselves are located in maximum -security facilities, 
which are provided with additional barriers to prevent any accidental 
release. Air locks, negative air pressure, clothes -change rooms, 
filtration and incineration of all air exhausted from the facility, and 
the secondary sterilization of all liquid and solid wastes provide 
additional protection to the environment. 
The NIH Guidelines also define requirements for protecting the 
environment from potential dangers that may be associated with the 
shipment of recombinant DNA materials. Federal packaging standards 
appropriate for the shipment of class 4 human etiologic agents are 
required for the shipment of all recombinant materials. 
