[Code of Federal Regulations] [Title 46, Volume 4] [Revised as of October 1, 2006] From the U.S. Government Printing Office via GPO Access [CITE: 46CFR98.25-70] [Page 85] TITLE 46_SHIPPING (This book contains parts 90 to 139) CHAPTER I--COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) PART 98_SPECIAL CONSTRUCTION, ARRANGEMENT, AND OTHER PROVISIONS FOR CERTAIN DANGEROUS CARGOES IN BULK--Table of Contents Subpart 98.25_Anhydrous Ammonia in Bulk Sec. 98.25-70 Venting. (a) Except as provided in paragraph (b) of this section, each safety valve installed on a cargo tank shall be connected to a branch vent of a venting system which shall be constructed so that the discharge of gas will be directed vertically upward to a point at least 10 feet above the weather deck or the top of any tank or house located above the weather deck. (b) The capacity of branch vents or vent headers shall depend upon the number of cargo tanks connected to such branch or header as provided in Table 98.25-70(b). Table 98.25-70(b)--Capacity of Branch Vents or Vent Headers ------------------------------------------------------------------------ Percent of Number of cargo tanks total valve discharge ------------------------------------------------------------------------ 1 or 2................................................... 100 3........................................................ 90 4........................................................ 80 5........................................................ 70 6 or more................................................ 60 ------------------------------------------------------------------------ (c) In addition to the requirement specified in paragraph (b) of this section, the size of the branch vents or vent headers shall be such that the back pressure in relief valve discharge lines shall not be more than 10 percent of the safety relief valve setting. (d) Return bends and restrictive pipe fittings are prohibited. Vents and headers shall be so installed as to prevent stresses on safety relief valve mountings. (e) When vent discharge risers are installed, they shall be so located as to provide protection against physical damage and be fitted with loose raincaps. (f) No shut-off valve shall be fitted in the venting system between the safety relief valve and the vent outlets. Suitable provision shall be made for draining the venting system if liquid can collect therein. [CGFR 65-50, 30 FR 17022, Dec. 30, 1965, as amended by CGFR 70-10, 35 FR 3712, Feb. 25, 1970; 35 FR 6431, Apr. 22, 1970]