Washington Administrative Code › Title 296 - Labor and Industries, Department of › Chapter 296-155 - Safety standards for construction work › Part Q - UNDERGROUND CONSTRUCTION › Section 296-155-74501 - Appendix A-Decompression tables

Current through Register Vol. 24-14, July 15, 2024
APPENDIX A-DECOMPRESSION TABLES
(1)
Explanation.
The
				decompression tables are computed for working chamber pressures from 0 to 14
				pounds, and from 14 to 50 pounds per square inch gauge inclusive by 2-pound
				increments and for exposure times for each pressure extending from one-half to
				over 8 hours inclusive. Decompressions will be conducted by two or more stages
				with a maximum of 4 stages, the latter for a working chamber pressure of 40
				pounds per square inch gauge or over.
Stage 1 consists of a reduction in ambient pressure ranging
				  from 10 to a maximum of 16 pounds per square inch, but in no instance will the
				  pressure be reduced below 4 pounds at the end of stage 1. This reduction in
				  pressure in stage 1 will always take place at a rate not greater than 5 pounds
				  per minute.
Further reduction in pressure will take place during stage 2
				  and subsequent stages as required at a slower rate, but in no event at a rate
				  greater than 1 pound per minute.
Decompression Table No. 1 indicates in the body of the table
				  the total decompression time in minutes for various combinations of working
				  chamber pressure and exposure time.
Decompression Table No. 2 indicates for the same various
				  combinations of working chamber pressure and exposure time the
				  following:
(a) The number of stages
				required;
(b) The reduction in
				pressure and the terminal pressure for each required stage;
(c) The time in minutes through which the
				reduction in pressure is accomplished for each required stage;
(d) The pressure reduction rate in minutes
				per pound for each required stage;
Important note:
The pressure reduction in each stage is
						  accomplished at a uniform rate. Do not interpolate between values shown on the
						  tables. Use the next higher value of working chamber pressure or exposure time
						  should the actual working chamber pressure or the actual exposure time,
						  respectively, fall between those for which calculated values are shown in the
						  body of the tables.
Examples:
Example No. 1:
4 hours working period at 20 pounds gauge.
Decompression Table No. 1:
20 pounds for 4 hours, total decompression
						  time.
43 minutes.
Decompression Table No. 2:
Stage 1: Reduce pressure from 20 pounds to
						  4 pounds at the uniform rate of 5 pounds per minute. Elapsed time stage 1:
						  16/5-
3 minutes.
Stage 2 (final stage): Reduce pressure at a
						  uniform rate from 4 pounds to 0-pound gage over a period of 40 minutes.
Rate-0.10 per pound per minute or 10
						  minutes per pound.
Stage 2 (final) elapsed time.
40 minutes.
Total time..................
43 minutes.
Example No. 2:
5-hour working period at 24 pounds gage.
Decompression Table No. 1:
24 pounds for 5 hours, total decompression
						  time.
117 minutes.
Decompression Table No. 2:
Stage 1: Reduce pressure from 24 pounds to
						  8 pounds at the uniform rate of 5 pounds per minute.
Elapsed time stage 1: 16/5
3 minutes.
Stage 2: Reduce pressure at a uniform rate
						  from 8 pounds to 4 pounds over a period of 4 minutes. Rate, 1 pound per minute
						  elapsed time, stage 2....................
4 minutes.
Transfer person to special decompression
						  chamber maintaining the 4-pound pressure during the transfer operation.
Stage 3 (final stage): In the special
						  decompression chamber, reduce the pressure at a uniform rate from 4 pounds to
						  0-pound gage over a period of 110 minutes. Rate, 0.037 pound per minute or 27.5
						  minutes per pound. Stage 3 (final) elapsed time......................
110 minutes.
Total time..................
117 minutes.