33 CFR §154.2109

1. (a)The inlet to a vapor recovery unit that receives vapor that has not been inerted, enriched, or diluted in accordance with 33 CFR 154.2107 must be fitted with a detonation arrester.
2. (b)The inlet to a vapor destruction unit must—
   1. (1)Have a liquid seal that meets the requirements of paragraph (e) of this section, except as specified by paragraph (b)(3) of this section; and
   2. (2)Have two quick-closing stop valves installed in the vapor line. One of them must be installed upstream of the detonation arrester required by paragraph (c)(2) of this section. The quick-closing stop valves must—
      1. (i)Close within 30 seconds after detection of a condition that requires the closing of these two quick-closing stop valves by a control component required by this subpart for a vapor control system (VCS) with a vapor destruction unit;
      2. (ii)Close automatically if the control signal is lost;
      3. (iii)Have a local valve position indicator or be designed so that the valve position is readily determined from the valve handle or valve stem position; and
      4. (iv)If the valve seat is fitted with resilient material, be a Category A valve as defined by 46 CFR 56.20-15 and not allow appreciable leakage when the resilient material is damaged or destroyed; and
   3. (3)Instead of a liquid seal as required by paragraph (b)(1) of this section, have the following:
      1. (i)An anti-flashback burner accepted by the Commandant and installed at each burner within the vapor destruction unit; and
      2. (ii)A differential pressure sensor that activates the quick-closing stop valves as required by paragraph (b)(2) of this section upon sensing a reverse flow condition.
3. (c)A vapor destruction unit must—
   1. (1)Not be within 30 meters (98.8 feet) of any tank vessel berth or mooring at the facility;
   2. (2)Have a detonation arrester fitted in the inlet vapor line; and
   3. (3)Activate an alarm that satisfies the requirements of 33 CFR 154.2100(e) and shut down when a flame is detected on the detonation arrester.
4. (d)When a vapor destruction unit shuts down or has a flame-out condition, the vapor destruction unit control system must—
   1. (1)Activate and close the quick-closing stop valves required by paragraph (b)(2) of this section;
   2. (2)Close the remotely operated cargo vapor shutoff valve required by 33 CFR 154.2101(a); and
   3. (3)Automatically shut down any vapor-moving devices installed in the VCS.
5. (e)If a liquid seal is installed at the inlet to a vapor destruction unit, then—
   1. (1)The liquid used in the liquid seal must be compatible with the vapors being controlled;
   2. (2)For partially or totally soluble cargoes that can polymerize in solution, there must be an adequate amount of inhibitor in the liquid seal;
   3. (3)The liquid seal must be compatible with the design of the VCS and must not contribute to the flammability of the vapor stream; and
   4. (4)The liquid seal must have a low-level alarm and a low-low level shutdown.