[Code of Federal Regulations]
[Title 49, Volume 3]
[Revised as of October 1, 2004]
From the U.S. Government Printing Office via GPO Access
[CITE: 49CFR193.2059]

[Page 129]
 
                        TITLE 49--TRANSPORTATION
 
 CHAPTER I--RESEARCH AND SPECIAL PROGRAMS ADMINISTRATION, DEPARTMENT OF 
                       TRANSPORTATION (CONTINUED)
 
PART 193_LIQUEFIED NATURAL GAS FACILITIES: FEDERAL SAFETY STANDARDS--
Table of Contents
 
                      Subpart B_Siting Requirements
 
Sec. 193.2059  Flammable vapor-gas dispersion protection.

    Each LNG container and LNG transfer system must have a dispersion 
exclusion zone in accordance with sections 2.2.3.3 and 2.2.3.4 of NFPA 
59A (incorporated by reference, see Sec. 193.2013) with the following 
exceptions:
    (a) Flammable vapor-gas dispersion distances must be determined in 
accordance with the model described in the Gas Research Institute report 
GRI-89/0242 (incorporated by reference, see Sec. 193.2013), ``LNG Vapor 
Dispersion Prediction with the DEGADIS Dense Gas Dispersion Model.'' 
Alternatively, in order to account for additional cloud dilution which 
may be caused by the complex flow patterns induced by tank and dike 
structure, dispersion distances may be calculated in accordance with the 
model described in the Gas Research Institute report GRI-96/0396.5 
(incorporated by reference, see Sec. 193.2013), ``Evaluation of 
Mitigation Methods for Accidental LNG Releases. Volume 5: Using FEM3A 
for LNG Accident Consequence Analyses''. The use of alternate models 
which take into account the same physical factors and have been 
validated by experimental test data shall be permitted, subject to the 
Administrator's approval.
    (b) The following dispersion parameters must be used in computing 
dispersion distances:
    (1) Average gas concentration in air = 2.5 percent.
    (2) Dispersion conditions are a combination of those which result in 
longer predicted downwind dispersion distances than other weather 
conditions at the site at least 90 percent of the time, based on figures 
maintained by National Weather Service of the U.S. Department of 
Commerce, or as an alternative where the model used gives longer 
distances at lower wind speeds, Atmospheric Stability (Pasquill Class) 
F, wind speed = 4.5 miles per hour (2.01 meters/sec) at reference height 
of 10 meters, relative humidity = 50.0 percent, and atmospheric 
temperature = average in the region.
    (3) The elevation for contour (receptor) output H = 0.5 meters.
    (4) A surface roughness factor of 0.03 meters shall be used. Higher 
values for the roughness factor may be used if it can be shown that the 
terrain both upwind and downwind of the vapor cloud has dense vegetation 
and that the vapor cloud height is more than ten times the height of the 
obstacles encountered by the vapor cloud.
    (c) The design spill shall be determined in accordance with section 
2.2.3.5 of NFPA 59A (incorporated by reference, see Sec. 193.2013).

[Amdt. 193-17, 65 FR 10959, Mar. 1, 2000, as amended by Amdt. 193-18, 69 
FR 11336, Mar. 10, 2004]

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