Review of Current Air Screening Procedures for Ballast Tank Diving

摘要

During underwater ship husbandry operations on submarines, divers enter the main ballast tanks to repair or modify electrical or mechanical systems. Before the divers are permitted to remove their diving equipment to increase their mobility, efficiency, and comfort during their work, gas free procedures are currently used to confirm the chemical safety of ballast tank atmospheres at pressures up to 2 atmospheres absolute (ATA). During multiple visits to two different shore sites where ballast tank diving was occurring, we reviewed these air screening methods and collected air samples from ballast tanks as a first step toward developing a uniform set of procedures to improve the ability to ensure safe, breathable air during ballast tank diving. The gas free procedures used at the two commands that we visited were similar but failed to screen for volatile organic compounds (VOCs), did not always test for 002, and were not always performed at hourly intervals during the diving operation. In view of the elevated levels of VOCs and 002 found in some of our samples, these screening failures put diver safety at risk. In our opinion, instead of gas free screening (with its ambiguity about what gases should be monitored), the emphasis of any air testing should be on ensuring a safe, breathable atmosphere inside the ballast tank during diving. Consequently, upon entry into ballast tanks, before diving equipment is removed, the ballast tank atmosphere should be evaluated for its chemical safety in terms of 02, 002, CO, and VOCs. The current approach of using the Occupational Safety and Health Administration (OSHA) guidance to set limits for 002 and CO appears reasonable, although a mechanism should be established to update U.S. Navy procedures when OSHA makes a substantial change in exposure limits.