Step 7. Corrected SPL. The corrected SPL equals the Estimated SPL from step 5 minus the reduction in dB from step 6. Enter the corrected SPL in step 7 of the worksheet.

Step 8. PEL Determination. Go to the SPL in the appropriate table and read one column right to find the PEL for the SPL shown in step 7 of the worksheet. Enter in step 8 of the worksheet.

Step 9. Duty Cycle/Adjusted PEL Calculation. Tables 1A-3 through 1A-6 assume a transmit duty cycle of 20 percent. Duty cycle (DC) is the percentage of time in a given period that the water is being ensonified (sonar transmitting). Sonar operators may use various means of computing DC that are valid for the purpose of this instruction. If the actual duty cycle is different from 20 percent, PELs may be extended or shortened proportionally. Use step 9 of the worksheet to calculate and enter the corrected PEL.

The formula for duty cycle is:

DC = 100 x Pulse length (sec.) / Pulse Repetition Period (sec.)

The formula for the adjusted PEL is:

Adjusted PEL = PEL x 20 / actual duty cycle; Equation 1

Example Problem. An un-hooded wet suited diver is 16 yards from an AN/SQQ-14 sonar transmitting a 500 msec pulse (.5 seconds) every 10 seconds.

Solution. The actual duty cycle (DC) % is:

Locate the PEL from the table (which is for a 20% duty cycle). Compute the adjusted PEL as:

Using worksheet step 9, Adjusted PEL = PEL (from step 8) 170 x 20/5=680 minutes.

If variable duty cycles are to be used, select the greatest percent value.

Step 10. Multiple Sonar/Noise Dose Calculation. When two or more sonars are operating simultaneously, or two or more periods of noise exposure of different values occur, the combined effects must be considered. In the following formula, ND is the daily noise dose and must not exceed a value of 1.0, DT is the dive (exposure) time (left surface to reach surface), and PEL is the PEL for each noise exposure condition computed as described above:

Note: DT1/PEL1 is for the first sonar, DT2/PEL2 is for the second sonar, up to the total number of sonars in use.

To use the worksheet, go through the steps 1-9 for each sonar, entering the appropriate values in each step of the worksheet. Enter the PELs into the worksheet step 10. There is room for two sonars in the worksheet. If more than two are being used, follow the same format and continue the calculations in the white space at the end of the worksheet.

Example Problem. A hooded wet suited diver is 100 yards from a transmitting AN/SQS-53A sonar and a transmitting AN/SQS-23 sonar for fifteen minutes.

Solution.

DT1 = 15 minutes

PEL1 (for SQS-53A) = 50 minutes DT1/PEL1 = 15/50 = .3

DT2 = 15 minutes

PEL2 (for SQS-23) = 285 minutes

This is less than 1.0 and therefore is acceptable.

Example 1: You are planning a routine dive for 160 minutes using wet-suited divers without hoods at a dive site 17 yards from an AN/SQQ-14 sonar. The duty cycle for the AN/SQQ-14 sonar is unknown. Is this dive permitted? Provide justification for your decision.

SONAR SAFE DIVING DISTANCE/EXPOSURE TIME WORKSHEET

1. Diver dress: Wet Suit - Un-hooded X

Helmeted _

5. Estimated SPL at range(s) in step 3 (from table/column in step 3): SPL = 198 dB

Reminder: If range is between two values in the table, use the shorter range. If the SPL is measured at the dive site, use the measured value.

6. Depth Reduction 0 dB

Reminder: 0 if not helmeted, see table in instructions if helmeted.

7. Corrected SPL (Step 5 minus Step 6) SPL1 198 - 0 = 198 dB

8. Estimated PEL at SPL (from table/column in step 3 of the appendix): PEL1 = 170 minutes

Adjusted PEL for actual duty cycle

Actual DC % = 100 x_sec. (pulse length /_sec. (pulse repetition period)

Adjusted PEL = PEL (from step 8)_min. x 20 / actual duty cycle (%)_=_min.

Reminder: Do not adjust the PEL if duty cycle is unknown.

Sonar 1: DT1 =_(Desired dive duration)

PEL1 =_(from Step 8 or 9, as applicable)

Sonar 2: DT1 =_(Desired dive duration)

PEL1 =_(from Step 8 or 9, as applicable)

ND =_+_=_ (This is less than 1.0, so dive is acceptable and may proceed.)

Reminder: The Noise Dose must not exceed a value of 1.0.

The dive time of 160 minutes is permitted because the PEL is 171 minutes.

Figure 1A-2. Sonar Safe Diving Distance/Exposure Time Worksheet (Completed Example).

Example 2: You are planning a routine dive for 75 minutes using wet-suited divers without hoods at a dive site which is 1000 yards from an AN/SQS-23 sonar. The SPL was measured at 185 dB. The duty cycle for the AN/SQS-23 sonar is unknown. Is this dive permitted? Provide justification for your decision.

SONAR SAFE DIVING DISTANCE/EXPOSURE TIME WORKSHEET

1. Diver dress: Wet Suit - Un-hooded X

Helmeted _

5. Estimated SPL at range(s) in step 3 (from table/column in step 3): SPL = 185 dB

Reminder: If range is between two values in the table, use the shorter range. If the SPL is measured at the dive site, use the measured value.

6. Depth Reduction 0 dB

Reminder: 0 if not helmeted, see table in instructions if helmeted.

7. Corrected SPL (Step 5 minus Step 6) SPL1 185 - 0 = 185 dB

8. Estimated PEL at SPL (from table/column in step 3 of the appendix): PEL1 = 170 minutes

Adjusted PEL for actual duty cycle

Actual DC % = 100 x_sec. (pulse length /_sec. (pulse repetition period)

Adjusted PEL = PEL (from step 8)_min. x 20 / actual duty cycle (%)_=_min.

Reminder: Do not adjust the PEL if duty cycle is unknown.

Sonar 1: DT1 =_(Desired dive duration)

PEL1 =_(from Step 8 or 9, as applicable)

Sonar 2: DT1 =_(Desired dive duration)

PEL1 =_(from Step 8 or 9, as applicable)

ND =_+_=_ (This is less than 1.0, so dive is acceptable and may proceed.)

Reminder: The Noise Dose must not exceed a value of 1.0.

The dive time of 75 minutes is permitted because the PEL is 170 minutes.

Figure 1A-3. Sonar Safe Diving Distance/Exposure Time Worksheet (Completed Example). APPENDIX 1A — Safe Diving Distances from Transmitting Sonar

Example 3: You are planning a 98 fsw dive for 35 minutes using the MK 21 at a dive site which is 3000 yards from an AN/SQS-53C sonar. The duty cycle for the AN/SQS-53C sonar is unknown. Is this dive permitted? Provide justification for your decision.

SONAR SAFE DIVING DISTANCE/EXPOSURE TIME WORKSHEET

Helmeted X

5. Estimated SPL at range(s) in step 3 (from table/column in step 3): SPL1 = 181 dB

Reminder: If range is between two values in the table, use the shorter range. If the SPL is measured at the dive site, use the measured value.

6. Depth Reduction 6 dB

Reminder: 0 if not helmeted, see table in instructions if helmeted.

7. Corrected SPL (Step 5 minus Step 6) SPL1 181 - 6 = 175 dB

8. Estimated PEL at SPL (from table/column in step 3 of the appendix): PEL1 = 50 minutes

Adjusted PEL for actual duty cycle

Actual DC % = 100 x_sec. (pulse length /_sec. (pulse repetition period)

Adjusted PEL = PEL (from step 8)_min. x 20 / actual duty cycle (%)_=_min.

Reminder: Do not adjust the PEL if duty cycle is unknown.

Sonar 1: DT1 =_(Desired dive duration)

PEL1 =_(from Step 8 or 9, as applicable)

Sonar 2: DT1 =_(Desired dive duration)

PEL1 =_(from Step 8 or 9, as applicable)

ND =_+_=_ (This is less than 1.0, so dive is acceptable and may proceed.)

Reminder: The Noise Dose must not exceed a value of 1.0.

The dive time of 35 minutes is permitted because the PEL is 50 minutes.

Figure 1A-4. Sonar Safe Diving Distance/Exposure Time Worksheet (Completed Example).

Example 4: You are planning a routine dive for 120 minutes using wet-suited divers with hoods at a dive site which is 200 yards from an AN/SQS-53A sonar and 120 yards from an AN/SQS-23 sonar. The AN/SQS-53A sonar is transmitting an 800 msec pulse (0.8 sec) every 20 seconds. The duty cycle for the AN/SQS-23 sonar is unknown. Is this dive permitted? Provide justification for your decision.

SONAR SAFE DIVING DISTANCE/EXPOSURE TIME WORKSHEET

Wet Suit - Hooded X Helmeted _

4. Range(s) to sonar (yards): 200 (from SQS-53A); 120 (from SQS-23)

5. Estimated SPL at range(s) in step 3 (from table/column in step 3): SPL1 = 201; SPL2 = 196 (per reminder, use SPL for 112 yard range)

6. Depth Reduction 0 dB

Reminder: 0 if not helmeted, see table in instructions if helmeted.

7. Corrected SPL (Step 5 minus Step 6) SPL1 201 - 0 = 201 dB; SPL2 196 - 0 = 196 dB;

8. Estimated PEL at SPL (from table/column in step 3 of the appendix): PEL1 = 143 min; PEL 2 = 339 min

Adjusted PEL for actual duty cycle

Actual DC % = 100 x 0.8 sec. (pulse length / 20 sec. (pulse repetition period) Actual DC % = 4

Adjusted PEL = PEL (from step 8) 143 min. x 20 / actual duty cycle (%) _4_ = 715 min. PEL1 = 715 minutes; PEL2 = 339 minutes Reminder: Do not adjust the PEL if duty cycle is unknown.

10. Multiple Sonars: Yes X (do step 10); No _(stop)

Sonar 1: DT1 = 120 (Desired dive duration)

PEL1 = 715 (from Step 8 or 9, as applicable) DT1/PEL1 = 120/715 = 0.17 .

Sonar 2: DT1 = 120 (Desired dive duration)

PEL1 = 339 (from Step 8 or 9, as applicable) DT1/PEL1 = 120/339 = .35 .

ND = 0.17 + 0.35 = 0.52 (This is less than 1.0, so dive is acceptable and may proceed.) Reminder: The Noise Dose must not exceed a value of 1.0.

The dive time of 120 minutes is permitted because the ND is less than 1.0.

Figure 1A-5. Sonar Safe Diving Distance/Exposure Time Worksheet (Completed Example). APPENDIX 1A — Safe Diving Distances from Transmitting Sonar

Permissible Exposure Limit (PEL) within a 24-hour period for exposure to AN/SQS-23, -26, -53, -56, AN/BSY-1, -2 and AN/BQQ-5 sonars, including versions and upgrades. Exposure conditions shown above the double line should be avoided except in cases of compelling operational necessity.

Estimated Ranges in yards for given SPL and PEL for sonar.

Was this article helpful?

## Post a comment