(a)   Scope. These rules are supplementary and additional to the requirements of §27-4116 of the Administrative Code providing for the use of methyl chloride in class B and class C refrigerating systems.  The promulgation of these rules has become necessary because of the military requirements for Freon (F12). Methyl chloride, while not permitted to be used in class A systems, is permissively allowed in class B and C systems. However, when used in refrigerating systems which formerly used Freon, additional precautions and safeguards are necessary to adapt the refrigerating equipment for use with methyl chloride.
   (b)   Prohibited uses of methyl chloride refrigerant.
      (1)   No direct system or indirect open spray system of air conditioning employing methyl chloride shall be permitted in a public building as defined in § C26-235.0.
      (2)   The direct method of refrigeration may be permitted when the installation satisfies the requirements of §27-4116 and only when the percentage of methyl chloride to the volume of conditioned space is not over .7 of 1 percent. (Methyl chloride to equal 8.0 cubic feet per lb.)
   (c)   Requirements for permissible uses of methyl chloride refrigerant in Class B and C refrigerating systems.
      (1)   That the refrigerating equipment room shall be isolated from human occupancies by reasonably gas tight opening closures.
      (2)   A mechanical exhaust system with a capacity of ten changes of air per hour shall be provided for the refrigeration equipment room and so controlled electrically and automatically that it shall start with the refrigerating system and be kept running while the system is in operation; that an independent switch remotely located and labeled shall be provided for the mechanical exhaust system so that such ventilating system may operate independently if it should become necessary to stop the refrigerating system during an emergency; that the intake to the exhaust fan shall be located as near the floor as practicable. The capacity of such ventilating system shall in no event be less than the requirements in § C19-99.b.3.*
      (3)   That the service company making the conversion shall check with the manufacturer of the specific equipment and certify in writing that conversion to methyl chloride can be safely made and shall list the changes in the system and controls as recommended by the manufacturer to make the equipment suitable for use with methyl chloride. The service company shall, after complying with the recommended changes by the manufacturer, certify to the Fire Commissioner that such recommended changes have been made and shall certify that all the requirements of these rules have been complied with.
         (i)   The system shall be completely purged of all Freon and the lubricating oil replaced with fresh oil suitable for use in refrigeration.
         (ii)   The system shall be thoroughly cleansed, dehydrated and tested for tightness and leaks by pressure immediately after methyl chloride is added. After the system has been purged as provided in §21-01(c)(3)(i) and before methyl chloride is added, special tubes shall be attached on the feed side of the line, containing either silica gel (high test solid material specifically designed for refrigerant drying), activated alumina or suitable drying agent to insure thorough dryness of the refrigerant.
         (iii)   Expansion valves shall be reset or replaced as required.
         (iv)   Relief valves and pressure limiting device shall be reset to conform to the Administrative Code requirements.
         (v)   All gaskets in the system shall be replaced with gaskets suitable for use with methyl chloride.
         (vi)   Only the exact amount of methyl chloride shall be charged into the system. Capacities shall be measured on the basis of weight of the refrigerant and not volume. Under no circumstances shall external heat, steam, open flame or otherwise, be applied to the cylinder containing the refrigerant and only the exact amount of refrigerant required for charging shall be permitted to be delivered to the premises. After charging, the cylinder shall be immediately disconnected and removed. No reserve storage of methyl chloride shall be permitted nor shall there be any open flames in the same room with the refrigeration equipment.
         (vii)   Before charging any refrigeration system with methyl chloride, all parts which are in contact with the refrigerant and are composed of aluminum, magnesium, zinc or their alloys, shall be replaced with parts made of suitable metals.
         (viii)   Upon completion of the conversion from freon to methyl chloride, and before the equipment is put in operation, the service company shall make a complete check for leaks using a Halide torch and immediately remedy any leaks.
         (ix)   A mask or helmet as approved by the Bureau of Mines of the U.S. Dept. of Interior for use with methyl chloride shall be provided in a suitable wall cabinet located immediately outside the equipment room.
         (x)   A weekly inspection by the person holding a certificate of fitness to supervise refrigerating equipment as provided in § C26-214.0 shall be made of the refrigeration equipment and all piping and connections for leakage.
         (xi)   Refrigeration equipment within the purview of these rules shall bear a metal sign reading: "Caution: Methyl Chloride Refrigerant, Guard Against Leaks."