Section 157.164 - Use of inert gas system(a) The master of a tank vessel having a COW system under § 157.10(e) , § 157.10a(a)(2) , or § 157.10c(b)(2) shall ensure the following: (1) Before each cargo tank is crude oil washed, the oxygen content in the tank is measured at each of the following locations in the tank: (i) One meter from the deck.(ii) In the center of the ullage space.(2) Before each cargo tank with partial bulkheads is crude oil washed, each area of that tank formed by each partial bulkhead is measured in accordance with paragraph (a)(1) of this section.(3) Before each cargo tank is crude oil washed, the oxygen content in that tank is 8 percent or less by volume at the locations under paragraph (a)(1) of this section.(4) During COW operations, the following are maintained in each cargo tank being crude oil washed: (i) A gas or a mixture of gases with an oxygen content of 8 percent or less by volume.(ii) A positive atmospheric pressure.(5) During COW operations, a crew member monitors the instrumentation under 46 CFR 32.53-60(a)(1) , except if that instrumentation has an alarm that sounds in the cargo control room when the oxygen content exceeds 8 percent by volume.(b) Crude oil washing of the cargo tanks must be terminated when paragraph (a)(4) of this section is not met and crude oil washing of that tank may not be resumed until the requirements of paragraph (a)(4) of this section are met.CGD 77-058b, 45 FR 43709, June 30, 1980, as amended by CGD 82-28, 50 FR 11628, Mar. 22, 1985