Section 84.84 - Hand-operated valves; minimum requirements(a) Hand-operated valves shall be designed and constructed to prevent removal of the stem from the valve body during normal usage to insure against a sudden release of the full pressure of the container when the valve is opened.(b) Valves shall be designed or positioned to prevent accidental opening and closing, and damage from external forces.(c) Valves operated during use of the apparatus shall be installed in locations where they can be readily adjusted by the wearer.(d) Main-line valves, designed and constructed to conserve gas in the event of a regulator or demand valve failure, shall be provided in addition to gas container valves, except when such failure will not affect performance.(e) Hand-operated bypass systems designed and constructed to permit the wearer to breathe and to conserve his gas supply in the event of a regulator or demand valve failure, shall be provided where necessary.(f) Valves installed on apparatus shall be clearly distinguishable from one another by sight and touch.(g) The bypass system valve control shall be colored red.(h) A main-line or bypass valve or system will not be required on apparatus for escape only.(i) Safety relief valves or systems, designed and constructed to release excess pressure in the breathing circuit, shall be provided on closed-circuit apparatus, and shall meet the following requirements:(1) The relief valve or system shall operate automatically when the pressure in the breathing circuit on the inhalation side of the breathing bag reaches 13 mm. (one-half inch) water-column height of pressure above the minimum pressure required to fill the breathing bag, within the breathing resistance requirements for the apparatus.(2) The relief valve or system shall be designed to prevent external atmospheres from entering the breathing circuit.(3) The relief valve or system shall be designed to permit manual overriding for test purposes and in the event of a failure in the valve or system.