Dive_Man_ChangeA

CHAPTER 8 — Surface-Supplied Air Diving Operations Change A 8-17 To meet these standards, specially designed compressors must be used with the air supplied passed through a highly efficient filtration system. The compressed air found in a shipboard service system usually contains excessive amounts of oil and is not suitable for diving unless filtered. Air taken from any machinery space, or downwind from the exhaust of an engine or boiler, must be considered to be contaminated. For this reason, care must be exercised in the placement and opera- tion of diving air compressors to avoid such conditions. Intake piping or ducting must be provided to bring uncontaminated air to the compressor. The outboard end of this piping must be positioned to eliminate sources of contamination. To ensure that the source of diver’s breathing air satisfactorily meets the standards estab- lished above, it must be checked at intervals not to exceed 8 months, in accordance with the PMS. 8-7.1.2 Air Supply Flow Requirements. The required flow from an air supply depends upon the type of diving apparatus being used. The open-circuit air supply system must have a flow capacity (in acfm) that provides sufficient ventilation at depth to maintain acceptable carbon dioxide levels in the mask or helmet. Carbon dioxide levels must be kept within safe limits during normal work, heavy work, and emergencies. If demand breathing equipment is used, such as the MK 21 MOD 1 or the MK 20 MOD 0, the supply system must meet the diver’s flow requirements. The flow requirements for respiration in a demand system are based upon the average rate of air flow demanded by the divers under normal working conditions. The maximum instantaneous (peak) rate of flow under severe work conditions is not a continuous requirement, but rather the highest rate of airflow attained during the inhalation part of the breathing cycle. The diver’s requirement varies with the respiratory demands of the diver’s work level. 8-7.1.3 Supply Pressure Requirements. In order to supply the diver with an adequate flow of air, the air source must deliver air at sufficient pressure to overcome the bottom seawater pressure and the pressure drop that is introduced as the air flows through the hoses and valves of the system. Table 8-2 shows the values for air consumption and minimum over-bottom pressures required for each of the surface-supplied air diving systems. Table 8-2. Primary Air System Requirements. Air Consumption System Minimum Manifold Pressure (MMP) Average Over Period of Dive (acfm) MK 21 MOD 1 (Depth in fsw 0.445) + 90 to 165 psi, depending on the depth of the dive 1.4 (Note 1) MK 20 MOD 0 (Depth in fsw 0.445) + 90 psi 1.4 Note 1: The manifold supply pressure requirement is 90 psig over-bottom pressure for depths to 60 fsw, and 135 psig over-bottom pressure for depths from 61-130 fsw. For dives from 131-190 fsw, 165 psig over-bottom pressure shall be used.