33 CFR § 401.68 - Explosives permission letter.
(a) A Seaway Explosives Permission Letter is required for an explosive vessel in the following cases:
(1) For all vessels carrying any quantity of explosives with a mass explosive risk, up to a maximum of 2 tonnes (IMO Class 1, Division 1.1 and 1.5);
(2) For all vessels carrying more than 10 tonnes and up to a maximum of 50 tonnes of explosives that do not explode en masse (IMO Class 1, Division 1.2);
(3) For all vessels carrying more than 100 tonnes and up to a maximum of 500 tonnes of explosives having a fire hazard without explosive effect (IMO Class 1, Division 1.3); and
(4) For all vessels carrying more than 100 tonnes and up to a maximum of 500 tonnes of safety explosives and shop goods (IMO Class 1, Divisions 1.4).
(b) When an explosive vessel is carrying quantities of explosives above the maximum mentioned in paragraph (a) of this section, no Seaway Explosives Permission Letter shall be granted and the vessel shall not transit.
(c) A written application for a Seaway Explosives Permission Letter certifying that the cargo is packed, marked and stowed in accordance with the Transportation of Dangerous Goods Regulations (Canada), the United States regulations under the Dangerous Cargo Act and the International Maritime Dangerous Goods Code, may be made to the St. Lawrence Seaway Management Corporation, 202 Pitt Street, Cornwall, Ontario, K6J 3P7, or to the Saint Lawrence Seaway Development Corporation, P.O. Box 520, Massena, New York, U.S.A. 13662.
(d) A signed copy of a Seaway Explosives Permission Letter and a true copy of any certificate as to the loading of dangerous cargo shall be kept on board every explosive vessel in transit and shall be made available to any officer requiring production of such copies.