Nasa expendable launch vehicle payload safety requirements: requirements table



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HAZARD AREA CLASSIFICATION


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Block #1:

  • Is the presence of flammable liquids or gases likely? (See Note 1) OR

  • Are combustible liquids having flash points at or above 100ºF likely to be handled, processed, or stored at temperatures above their flash points? (See Note 2)

Block #3:

  • In an adequately ventilated location, are flammable substances contained in a suitable, well-maintained, closed piping system that includes only the pipe, valves, fittings, flanges, and meters? (See Note 3) OR

  • In an adequately ventilated facility, are flammable substances contained in piping systems without valves, fittings, flanges, and similar accessories? (See Note 4) OR

  • Are flammable liquids or gases in suitable containers? (See Note 5) OR

Block #4:

  • Is the flammable gas concentration likely to exist in the air under operating conditions? OR

  • Is a flammable atmospheric concentration likely to occur frequently because of maintenance, repairs, or leakage? OR

  • Would a failure of process, storage, or other equipment be likely to cause an electrical system failure creating an ignition source simultaneously with the release of a flammable liquid or gas? OR

  • Is the flammable liquid or gas piping system in an adequately ventilated location, and is the piping system (containing valves, meters, or screwed or flanged fittings) poorly maintained? OR

  • Is the location lower than the surrounding elevation or grade so that flammable liquids or gases may accumulate there?

Block #6:

  • Is the flammable liquid or gas piping system in an adequately ventilated location, and is the piping system (containing valves, meters, or screwed or flanged fittings) well-maintained? OR

  • In a process equipment system containing flammable liquids or gases in an adequately-ventilated location (exclusive of well-maintained piping system), can the liquid or gas escape from such potential sources as pumps seals, atmospheric vents, or relief valves, sample stations, drains, and so forth, as a result of an abnormal condition? (see Note 6) OR

  • Is the location adjacent to a Division 1 location, or can the gas be conducted to the location, as through trenches, pipe, or duct? OR

  • If positive mechanical ventilation is used, could failure or abnormal operation of ventilating equipment permit atmospheric vapor mixtures to build up to flammable concentrations? (See Note 7)



chart1 (2)

Figure A3.1. Flow Path.

NOTES:

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1. The following are considered flammable liquids/gasses:

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a. Unsymmetrical dimethylhydrazine (UDMH) - Flashpoint *(Closed Cup) 5×F.

Note: There is conflicting information in available literature that presents the closed cup flashpoint of UDMH to be either 5oF or 35oF.
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b. Monomethyl hydrazine (MMH) - Flashpoint* (Closed Cup) 17×F.

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2. Hydrazine (N2H4) - is considered a combustible liquid.

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a. The surface temperature of potential spill areas must also be considered.

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b. Temperature in the area must be single failure tolerant to remain below the flashpoint (Closed Cup) of 1000F.

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c. Below grade locations may still accumulate enough N2H4 to become flammable at lower temperatures.

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3. Adequate ventilation is defined by NFPA 30, Flammable and Combustible Liquids Code, as that which is sufficient to prevent the accumulation of significant quantities of vapor-air mixtures in concentrations over 25 percent of the lower flammability limit.

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a. An adequately ventilated location is one of the following:

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(1) An outside location.

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(2) A building, room, or space that is substantially open and free of obstruction to the natural passage of air, either vertically or horizontally. Such locations may be roofed over with no walls, may be roofed over and closed on one side or may be provided with suitably designed wind breaks.

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(3) An enclosed or partly enclosed space provided with mechanical ventilation equivalent to natural ventilation. The mechanical ventilation system must have adequate safeguards against failure.

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b. Lower flammability limits of specific commodities are as follows:

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(1) N2H4 - 4.7 percent.

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(2) MMH - 2.5 percent.

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(3) UDMH - 2.0 percent.

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(4) Aerozine 50 - 2.0 percent.

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c. Payload propellant systems cannot normally be considered closed piping systems that include only the pipe, valves, fittings, flanges, and meters; they normally also include a pressure vessel.

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4. Payload propellant systems cannot normally be considered piping without valves, fitting, flanges, and similar accessories.

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5. Payload propellant systems cannot be considered suitable containers unless they meet DOT or ASME requirements or meet Volume 3, Chapter 12 of this publication and are also protected from outside damage.

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6. If this system is poorly maintained, this location shall be classified Class I, Division I per Diamond 4, item 4 above. Thus there is not a "no" answer to this question leading to non-classification.

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7. A payload propellant system would normally be considered a process equipment system. In a dynamic mode, the answer to this question will almost always be “yes;” in a static mode, the answer may be “yes” or “no” depending on past history and adequacy of protection from outside damage.

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8. An analysis shall be provided. Consideration shall be given to the size of the containment area, credible potential size of the spill, adequacy of the ventilation equipment and its potential failure modes, and the specific gravity of the commodity in question.

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