Explain the difference between gauge pressure and absolute pressure?
Gauge pressure indicates the difference between atmospheric pressure and the pressure being measured. Absolute pressure is the total pressure being exerted, i.e. gauge pressure plus atmospheric pressure.
List the factors that result in the pressure acting on a diver under the sea.
Atmospheric pressure, water pressure
State Archimedes's Principle.
Any object wholly or partly immersed in a fluid is buoyed up by a force equal to the weight of the fluid displaced by the object.
Is it easier for an object to float in seawater or fresh water? Why?
Seawater, weight is 64lbs per cubic ft
Name a specific diving related problem that is directly related to Boyle's Law.
Pulmonary over inflation syndrome (pois) arterial gas embolism (age)
Which gas law explains why as a diver goes deeper more gas dissolves In his tissues?
Henry's law, the amount of any given gas that will dissolve in a liquid at a given temperature is directly proportional to the partial pressure of that gas. 2-12.6
State Charles/Gay-Lussac's Law.
At a constant pressure, the volume of a gas is directly proportional to the change in the absolute temperature. If the pressure is kept constant and the absolute temp is doubled the volume will double.
What happens to light as it travels to depth in clear water?
Colors are filtered out of light as it enters the water and travels to depth, (red, orange, yellow, green, blue, indigo, violet (roy g biv).
The amount of nitrogen absorbed in the body depends on what three factors?
Time, pressure, temp
What is the rate of ascent when surfacing from a dive?
What is a good "rule of thumb" during ascent while conducting a SCUBA dive so as not to exceed the ascent rate?
Don't travel faster than your smallest bubbles.
Define residual nitrogen and Residual Nitrogen Time (RNT).
The time that must be added to the bottom time of a repetive dive to compensate for the nitrogen still in a diver's tissues form a previous dive.
Up to what altitude may normal air decompression tables be used?
Up to 300ft, between 300ft and 1000ft correction is required for dives deeper than 145fsw. Above 1000ft correction is required for all dives.
. What must be considered if you are planning to dive within a 12-hour period of ascending to altitude?
12 hours at attitude is required for equilibration. If a dive begins within 12hr of arrival, the residual Nitrogen left over from sea level must be taken in to account.
Who can provide altitude tables above 10,000 feet when authorization is granted?
How can you ensure that the selected decompression schedule is always conservative?
Always select the schedule depth equal to or next greater than the maximum depth of the dive and always select the schedule bottom time equal to or next longer than the bottom time of the dive.
What is a repetitive dive?
Any dive conducted within 12hr of a previous dive.
What is TDT and how is it figured?
Total decompression time (computed from leaving the bottom to reaching the surface)
Define bottom Time.
The total elapsed time from when the diver leaves the surface to the time they begin their ascent from the bottom. Measured in minutes and is rounded up to the next whole minute.
When a diver is extremely cold, what course of action can be taken regarding decompression?
Select the next longer decompression schedule than the one that would normally be used.
If a diver is ascending too fast, what should be done?
STOP THE ASCENT allows the watches to catch up, and then continue ascent. If the stop is arrived at early, start the stop time when the watches catch up.
By controlling our ascent, dissolved gas will be carried to the lungs and exhaled before it accumulates sufficiently to form bubbles in the tissues. Which gas law explains this release?
Henry's law, the amount of any given gas that will dissolve in a liquid at a given temp is directly proportional to the partial pressure of that gas.
What is the disadvantage of nitrogen when used in diving at deep depths?
. State the RNT exception rule?
When the repetive dive is to the same or greater depth than the previous dive, the RNT may be longer than the actual bottom time of the previous dive. In this event the actual bottom time or equalvant single dive time (ESDT) of the previous dive to the actual bottom time of the repetive dive to obtain ESDT.
Descent time is considered part of your _____ time.
If two divers on the same dive have different deepest depths, how do you figure for decompression?
Use the deepest depth of the two.
Explain the primary reason exceptional exposure dives are considered dangerous.
The risk of decompression sickness, O2 toxicity, and/or exposure to the elements is substantially greater than on normal working dives. The long deco times associated with exceptional exposure dives impose unusual demands on a diver's endurance. Also limited assurance that the dive will be completed without decompression sickness.
List the two conditions that must be met in order to use the RNT exception rule.
Repetive dive, same or grater depth.
The time from when the divers leave the surface to leaving the bottom on a dive is called Bottom Time. What is the time from when the divers leave the bottom until they reach the surface called?
Total decompression time
Define Max depth and Stage depth!
Max depth, the deepest depth attained by the diver plus the pneumofathometer correction factor (table 9-1) when conducting SCUBA, max depth is the deepest gauge reading. Stage depth, is the pneumofathometer reading taken when the divers are on the stage just prior to leaving the bottom. Stage depth is used to compute the distance and travel time to the first stop, or to the surface if no stops are required.