Although beneficial, knowing the cause and mechanics of Lung Over-Expansion injuries should never alter our first aid response. 

Whether the over-expansion injury is a pneumothorax, mediastinal emphysema, subcutaneous emphysema or an embolism first aid remains the same - lifeline, O2, call for help.

Once a patient is under the care of a medical facility and diagnosis has been reached, the treatment for the previously mentioned injuries can ve#ary greatly. 

Due to the increased density of water and it's increased elasticity sound travels approximately four times faster through water than through air.

This is also dependant on the temperature of the water and also how deep you are and the distance from the sound source. 

Slack tide is the time in which there is minimal movement between a flood and ebb tides. This can make it easier to enter exit on some shore entries and may have a reduction of water movement on a dive depending on the topography.

Diving at slack high tide is seen as a general rule so local dive knowledge is imperative before diving unfamiliar dive sites. 

PADI Divemaster's may continue their education by becoming Specialty Instructor's in Coral Reef Conservation, AWARE, DUP, Emergency Oxygen, Equipment Techniques as well as other pre-approved Distinctive Specialities if they meet course prerequisites and attend and successfully complete Specilaty Instructor Training with a PADI Course Director certified to conduct that PADI Specialty.

You can reference this in your PADI Instructor Manual - PADI Professional Ratings - Specialty Instructor.

I often see candidates mixing up questions pertaining to the first and second stage of the regulator. 

The piston and diaphragm are essentially two different mechanisms that do the same thing, allow the first stage to fill from high pressure and feed the hoses at an intermediate pressure.

Some questions that ask about pilot valves and downstream valves are relevant to the second stage, not the first stage.