Tariff Concession Order 0935393 declares a specific class of storage trailers (HS 8716.31.00) — with at least three pneumatic tanks >10 m3 each, a surge tank, discharge and fill/vent manifolds, and an onboard compressor — eligible for Item 50 of Schedule 4 from 21 Sept 2009 (made under s.269P).
Mechanically, importers of matching trailers can claim the Schedule 4 concession (reducing or removing import duty); the order is revocable by the delegate under ss.269SC–269SD and eligibility depends on customs classification and documentary evidence.