Interpretation ID: nht80-1.15
DATE: 02/08/80
FROM: AUTHOR UNAVAILABLE; F. Berndt; NHTSA
TO: Office of Vehicle Safety Compliance - Enforcement
TITLE: FMVSS INTERPRETATION
TEXT:
DATE: Feb. 8, 1980
SUBJECT: Request for Interpretation of Fuel Tank Capacity as used in Safety Standard No. 301-75, Fuel System Integrity
FROM : Chief Counsel
TO : Director, Office of Vehicle Safety Compliance, Enforcement
This confirms the oral response previously given by Hugh Oates to your memorandum requesting an interpretation of the term, "capacity", as used in Safety Standard No. 301-75. Paragraph S7.1.1 of that standard provides that "the fuel tank is filled to any level from 90 to 95 percent of capacity with Stoddard solvent ...." You ask whether "capacity" should include the vapor volume in the air dome plus the volume of the fuel filler pipe when filling a fuel tank for compliance purposes. (Total tank volume = usable capacity + unusable capacity + vapor volume + fluid in filler pipe.) Apparently, the vapor volume can be filled with solvent if the solvent is added very slowly to force the air vapors out of the dome. This has been done in past compliance testing.
It is our opinion that the term, "capacity", should not be interpreted to include the vapor volume in the air dome, since fuel tanks are never filled to this level by vehicle users. Fuel tanks are designed to include an area for fuel vapor and pressure build- up. Vehicle users never fill their tanks so slowly that this area is displaced with fuel. Therefore, it would be an unrealistic test to require manufacturers to fill tanks in this fashion. Moreover, I understand from convervations between our offices that fuel is actually squeezed out of the filler pipe during compliance testing if the tank is filled to this absolute level. This would not seem to be an accurate test of fuel tank integrity, since it is leaks or punctures in the tank itself that generally cause fuel loss in real-world crashes.
In consideration of these facts, we would interpret "capacity" to mean "usable capacity", as used in the vehicle manufacturer's Part I submission to the EPA, plus "unusable capacity" (i.e., the volume of fuel left in the tank when the engine fuel pump sucks air).
I think it should be emphasized that the "usable capacity" should be determined only after the tank has been filled to its "unusable capacity". In other words, when testing a tank that has never been filled, the unusable, residual fuel level should be reached before the "usable capacity" is added to the tank. If this is not done, the actual volume of fuel in the tank will be somewhat below the "usable fuel capacity".
Frank Berndt
February 20, 1980
Note From Tom Grubbs FMVSS 301-75 Safety Compliance Engineer Office or Vehicle Safety Compliance
As of February 20, 1980, all FMVSS 301-75 vehicle compliance tests will use the following fuel tank filling technique:
1. Test vehicle's engine will be "run dry"*.
2. 95% of the "usable capacity" of the fuel tank (as determined from EPA Part I submissions) will be added.
*After "run dry", the fuel left in the tank will be the "unusable capacity".
November 25, 1979
Request for Interpretation of Fuel Tank Capacity as used in FMVSS No. 301-75, "Fuel System Integrity" NEF-31TGr
Director Office of Vehicle Safety Compliance Enforcement Office of the Chief Counsel National Highway Traffic Safety Administration
THRU: Associated Administrator for Enforcement In order to preclude controversies during the FY 1980 FMVSS No. 301-75 vehicle safety compliance testing program, it is requested that an interpretation of "capacity" be issued by your office. At the present time, S7.1.1 of FMVSS No. 301- 75 states, "The fuel tank is filled to any level from 90 to 95 percent of capacity with Stoddard solvent...." The word "capacity" can be interpreted to mean one of the following: 1. Total Tank Volume - The unusable tank capacity plus the usable capacity plus the vapor volume in the air dome plus the volume of solvent in the fuel filler pipe as shown on the attached sketch. In order to completely fill the total tank volume, the solvent must be added slowly to force the air/vapors out of the air dome which is presently being performed by the OVSC testing laboratories. The vehicle manufacturers claim that this is not a realistic fuel tank filling technique.
2. Usable Capacity - The usable capacity of the fuel tank as stated in each vehicle manufacturers' Part I submission to the EPA. Some manufacturers are using 95 percent of this "usable capacity" value for their FMVSS No. 301-75 certification tests. It appears that this would be the most realistic fuel tank filling technique.
The FY 1980 FMVSS No. 301-75 vehicle compliance testing program will be initiated during the first week of January 1980, and it is requested that an interpretation be made prior to that time.
Francis Armstrong
Attachment
NEF-31TGrubbs:vgw:11/21/79:62807
cc: NEF-01 Chron NEF-30 Chron NEF-31 Subj/Chron/TGrubbs/File
LEFT SIDE VIEW OF TYPICAL GM FUEL TANK IN 1980 MODEL
*INSERT DIAGRAM HERE