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25 Cards in this Set
- Front
- Back
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What are the values that must me known in order to calculate the safe diving distance from transmitting sonar? |
a. Type of diving dress
b. Type of sonar being transmitted c. Distance from sonar |
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What does the acronym SPL stand for in regards to sonar?
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Sound Pressure Level (SPL)
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What does the acronym PEL stand for in regards to sonar?
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Permissible Exposure Limit (PEL)
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What is the determining factor for establishing Permissible Exposure Limit (PEL)?
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Sound Pressure Level (SPL), not distance
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What does the acronym LFA stand for in regards to sonar?
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Low-Frequency Active sonar (LFA)
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As Sound Pressure Level (SPL) increases above 215 dB for hooded divers, what are some of the effects may be noticed?
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a. Slight visual-field shifts (probably due to direct stimulation of the semicircular canals)
b. Fogging of the face plate c. Spraying of any water within the mask d. Other effects may occur |
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In the presence of long sonar pulses (one second or longer), what are some of the effects may be noticed?
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a. Depth gauges may become erratic
b. Regulators may tend to free-flow |
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Exposure of divers above _____ dB at any frequency is prohibited unless full wet suits and hoods are worn because the probability of physiological damage increases markedly.
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200 dB
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Fully protected divers (full wet suits and hoods) must not be exposed to SPLs in excess of ______ dB at any frequency for any reason.
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215 dB
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What size wet suits and hoods are recommended to protect from underwater sonar?
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3/8 inch
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What is the difference between In-water hearing and In-gas hearing?
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a. In-water hearing occurs when the skull is directly in contact with the water, as when the head is bare or covered with a wet-suit hood. In-water hearing occurs by bone conduction - sound incident anywhere on the skull is transmitted to the inner ear, bypassing the external and middle ear.
b. In-gas hearing occurs when the skull is surrounded by gas as in the MK 21 diving helmet. In-gas hearing occurs in the normal way - sound enters the external ear canal and stimulates the inner ear through the middle ear. |
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What are the three types of diving dress used when determining the calculations for sonar safe diving distance/exposure time worksheets?
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a. Wet suit or swim suit – un-hooded
b. Wet suit – hooded c. Helmet |
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If the type of sonar is unknown, start diving at _______ - _______ yards, depending on diving equipment (use greater distance if helmeted), and move in to limits of diver comfort.
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600–3,000 yards
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If range is between two values in the depth reduction table, which range do you use?
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Use the shorter range. This will insure that the SPL is not underestimated and that the PEL is conservative.
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What happens to the sensitivity to sound pressure as depth increases in helmeted divers?
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Sensitivity is reduced
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What is a Duty cycle (DC)?
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The percentage of time in a given period that the water is being insonified (sonar transmitting)
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The PEL tables are accurate to what % of DC?
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20%
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If the actual duty cycle is different from 20 % what are your actions?
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PELs may be extended or shortened proportionally. Use formula for determining adjusted PEL
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SPL is measured in dB/1 μPA at the dive site. How do you convert SPL for sound levels referenced to mbar?
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Subtract 100 dB from tabled levels
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When computing for multiple sonar exposure, the Noise Dose must not exceed what value?
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1.0
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If possible, you should avoid diving in the vicinity of what type of sonar?
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Low-Frequency Sonar (LFS)
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What are the possible effects of diving near Low-Frequency Sonar (LFS)?
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a. Sensations may include mild dizziness
b. vertigo c. Skin tingling d. Vibratory sensations in the throat e. Abdominal fullness f. Voice communications are likely to be affected by the underwater sound to the extent that line pulls or other forms of communication may become necessary. Annoyance and effects on communication are less likely when divers are wearing a hard helmet (MK 21) diving rig. |
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Who do you contact for safe diving distance guidance involving Low-Frequency Sonar (LFS)?
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NAVSEA (00C3)
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What is the primary effect of ultrasonic sonar?
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Heating
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What are the stipulations when diving near ultrasonic sonar?
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The frequencies used in ultrasonic sonars are above the human hearing threshold. Because the power of ultrasonic sonar rapidly falls off with distance, a safe operating distance is 10 yards or greater. Dive operations may be conducted around this type of sonar provided that the diver does not stay within the sonar’s focus beam. The diver may finger touch the transducer’s head momentarily to verify its operation as long as the sonar is approached from the side.
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