153.406—Standards for containment systems having required restricted gauges.

When Table 1 requires a cargo's containment system to have a restricted gauge, the containment system must have:

(a) A closed gauging system; or

(b) A system that has:

(1) A restricted gauge (e.g., a sounding tube) with an orifice diameter not exceeding 20 cm (approx. 7.8 in.);

(2) A permanently attached gauge cover that is vapor tight when in place; and

(3) A venting system that has either:

(i) Lock open PV valves; or

(ii) Valved bypasses around the PV valves.

CFR