Section 153.1108 - Heated prewash for solidifying NLS, high viscosity NLS and required prewashes of NLS whose viscosity exceeds 25 mPa sec at 20°C: Categories A, B, and C(a) When a high viscosity or solidifying cargo is unloaded from a cargo tank, the cargo tank must be prewashed unless § 153.1114 or paragraph (c) of this section allows the prewash to be omitted.(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.CGD 81-101, 53 FR 28975, Aug. 1, 1988 and 54 FR 12629, Mar. 28, 1989