25 October 2004
c) Air envelope around the plane, which excludes the "empty" area where there will be no
d) Full opening of the hangar, for instance the approximate side of the hangar door opening
plus about 5 feet on the top and sides of the hangar reserved for maneuverability?
e) Full opening of the hangar including open space for roof trusses?
Naval Facilities Engineering Command (NAVFAC) assigned the NAVOSH Air Branch of NFESC to
revise Military Handbook 1003/17, Industrial Ventilation Systems. The handbook defines
engineering design criteria for use by all components of the Department of Defense. We are
adding a new chapter to the MIL-HDBK discussing the criteria for spray painting in aircraft hangars.
We are having difficulties applying the interpretation to our criteria. To add to the urgency,
NAVFAC is also in the process of designing several new aircraft hangars. Reducing the flow rate
from 100 cubic feet per minute per square foot of cross-sectional area will provide a significant
reduction in equipment first costs and annual operating costs.
Our position is - Aircraft hangars should not be designed for 100 cubic feet per minute per square
foot of cross-sectional area due to the size of the space and the dilution effect. Regardless of the
flow rate, not all the paint overspray will reach the filters and we acknowledge some will drop to the
floor. This is particularly true for the portion of the aircraft farthest from the exhaust filter bank.
Paint spray criteria in the ACGIH Industrial Ventilation Manual permits airflow in large spaces as low
as 50 cubic feet per minute per square foot of cross-sectional area. Both the NFPA 33 and the
ANSI Z9.3 consensus standards require a sufficient ventilation rate to prevent vapor build-up by
requiring airflow to keep the vapor less than 25% of the LEL. Airflow calculations based on LEL are
typically 10-25% of the rates required for health protection. Enclosure (4) reiterates our
understanding of the pertinent regulations.
Our experience shows that even in spray painting operations using flow rates of 100 cubic feet per
minute per square foot of cross-sectional area, some employee's occupational exposure exceeds
the PEL for certain paints and paint components. Therefore, our employees use respiratory
protection when painting in hangars.
Thank you for continuing to consider our concern. Based on our phone conversation today, I
understand that you are also working on this issue with the US Air Force. Could you direct us to
their point of contact? Our contacts are Kappy Paulson and Trinh Do (805) 982-4984.