(b) When a prewash is required for a tank that has unloaded a solidifying cargo or a cargo having a viscosity exceeding 25 mPa sec at 20 °C, the wash water used in the prewash must leave the tank washing machine at a temperature of at least 60 °C (140 °F).
(c) The prewash required under paragraph (a) of this section may be omitted if the approved Procedures and Arrangements Manual contains a procedure for measuring the temperature of all interior cargo tank surfaces throughout unloading and under the measuring procedure the temperature of these surfaces remains above -
(1) The temperature of the cargo's melting point if the cargo is a Category B or C solidifying NLS; or
(2) The temperature at which the cargo's viscosity exceeds -
(i) 25 mPa.s, if the cargo is a high viscosity Category B NLS; or
(ii) 60 mPa.s, if the cargo is a high viscosity Category C NLS.