Dr. Donald F. Fredrickson, Director 
- 2 - 
August 21, 1978 
2. Page 33075, Section ll-B-4-c-(12) states "The exhaust air from the P-4 facility 
shall be filtered and discharged to the outdoors". I noted that the abbreviation 
HEPA had been omitted before the word "filtered". This may have been done 
inadvertently, but certainly should be reinstated since without HEPA filters there 
is no reason for certification testing as referred to at the end of this paragraph. 
3. Page 33075, Section II— B— 4— c— (14), the reference to "The exhaust air from the 
suit area shall be filtered by two sets of HEPA filters installed in series and a 
duplicate filtration unit and exhaust fan shall be provided." probably has been 
highly contested. Logically, if a substance passes the first filter it will also pass 
the second in the series since both filters are of the same arresting capacity. 
However, should the one filter rupture due to unforseen circumstances, the other 
filter would still maintain the integrity of the system. The duplicate filtration 
system could also be arranged to automatically be put into service should the 
primary filters or fan fail, thereby maintaining the constant negative pressure so 
necessary for the suit area. 
In this same section, the second paragraph states, "The internal shell of the suit 
area shall be airtight." This should be qualified either by making it comparable 
to the language used on previous page. Section 1 1— B— 4— c— (12) or stating the 
permissible leakage rate similar to that used in the table concerning the tightness 
of Biological Safety Cabinets. The specific gas to be used for testing the tightness 
should be so stated not only in this case, but also for the Biological Safety Cabinets. 
I trust the above will be considered of some value in finalizing the revision to the guidelines. 
I have not offered comments on the biological aspects of containment because this is beyond 
the scope of my ability as an engineer. 
Sincerely yours. 
John P. Hutten, Project Engineer 
JPH:sh 
[A-30] 
