IDC & Dive Masters Cheat Sheet For Scuba Diving

Equations, Meanings and Terms

Reflex Respiratory Centre – Detects High Carbon dioxide

Hypoxia – Insufficient Oxygen

Anoxia – Severe Oxygen Depletion

Hypocapnia – Insufficient Carbon Dioxide

Hypercapnia – Excess Carbon Dioxide

Bradycardia – Slowing of the Heart (Cold moisture on face)

Apnea – Breath Holding

It takes 8-12 hours to eliminate carbon monoxide


Water displacement (saltwater)

Ltrs x 1.03 = A

Object weight – A = B

B / 1.03 = Answer to bring an item to surface

(To make an object positively buoyant, add kg to B then / by 1.03)

If an object is on the surface and you want to know its displacement, object kg / 1.03 = answer

Water displacement (freshwater)

Ltrs x 1 = A

Object weight – A = B

B / 1 = Answer to bring an item to surface

Gauge Pressure in Fresh Water

Depth x .097 = Answer

Absolute Pressure in Fresh Water

Depth x .097 = A + I = Answer

Gas Expansion (inflexible container)

Ltrs of air x ata = Answer

Gas compression (in a flexible container)

Ltrs of air / ata = Answer

Heat Loss in Water

20 Times Faster Than Air


33% Magnification

Visual Reversal

Turbidity causes objects to look further away than they really are.


Travels 4 Times Faster in Water

Air Consumption

Bar per minute at surface x Absolute pressure

e.g 1.42 bar per minute x 3.2 (22 mtrs + 1) = 4.54

Gas Pressure and Liquid

Dissolved gas will enter liquid as the pressure increases and will come out of solution when pressure decreases.

When gas pressure in the solution exceeds the pressure outside of it.

For every deg of heat, gas pressure will change by 0.6 ata bar.

Partial Pressure

Air is .21 Oxygen and .79 Nitrogen

(For every 10 mtrs of s.w you add above again, e.g. at 20 mtrs Oxygen is .63 and Nitrogen is 2.37)


When gas pressure in the solution exceeds the pressure outside of it.

Heat and Pressure

For every deg of heat, gas pressure will change by 0.6 ata bar


Heat Exhaustion

Weak rapid pulse, rapid breathing, Profuse sweating, Skin cool and clammy, Nausea, May drink non-alcoholic fluid

Heat Stroke

Steady rapid pulse, Perspiration ceases, and Skin is flushed and hot, Nil by mouth, contact EMS

Oxygen Admin

Administer for all types of DCS and AGE, helps eliminate Nitrogen and raises blood oxygen levels

A Squeeze

Failure to equalise a body air space, middle ear most effected.


Round window rupture can occur if forceful blows against a pinched nose are done.

carotid sinus reflex

Excessively tight neck seal or hood

Nitrogen Narcosis

Foolish behaviour as if intoxicated


A substance that aids in the transport of oxygen, carbon monoxide bonds 200 times more readily to it.

Lung over-expansion

(Pneumpthorax, Air Embolism, Mediastinal Emphysema, Subcutaneous Emphysema) Symptoms are immediate as diver surfaces, Blurred vision, headache, confusion, unconsciousness, severe chest pain, foamy bloody mouth, difficulty Breathing, even death!


Symptoms are usually slower to occur, Skin rashes, joint and limb pain, pins and needles, numbness, over tiredness!

Scuba Diving Equipment


Aluminium tanks have thicker walls than steel. Heat can weaken the tank, and hydrostatic test are filled to higher than its working pressure, visual inspections check for damage, allow for maintenance and is a dive industry standard.

Burst Disk

Prevents a cylinder from being over pressurised


A regulator will free flow rather than shut off the air

Downstream valve

Opens with the flow of air

Pilot Valve

A small valve that opens a larger valve in the second stage

Delivers intermediate pressure to the second stage

First stage regulator


Equipment should be oxygen clean if over 40% of 02 is being used or if local regulations/equipment manufactures require it.


Serves as a warning device to tell the diver that they are low on air, should be open (down position) when being filled

Dive Skills and the Environment


High tide, slack is the best time to dive.


Break when the depth is the same height as the wave and are caused by the wind

Directional information in the water

Comes from plants, animals, noises, topography light and shadows

Near drowning

The patient should be advised to have medical attention, even if they feel fine

Safety Stop

Should be done after a long or deep dive, near no-decompression limits or at the end of any dive, air permitting.

Proper Weighting

Empty BCD, holding a normal breath, should float at eye level

Reciprocal Compass Heading

180 deg from initial heading


Are affected by the position of the sun, moon and earth

Lifting Devices

Should be used when an object is 4-7kg neg buoyant

Decompression theory and the RDP


The rate in which a theoretical tissue absorbs and releases Nitrogen


Any question solely on the RDP, answers will be found on it.

Dive Computers

Follow the same theoretical basis as dive tables, same recommendations as dive tables calculates the dive precisely,

Should not be shared.

Emergency decompression stop

If missed, don ‘t dive for 24hrs, rest, monitor yourself for DCS, breath 02 if available.

RDP Model

Characterised by 14 compartments and a 60-minute surface interval washout


Special procedures should be used higher than 300 Mtrs 1000 ft


With repetitive dives, an extended time over 12hrs, the longer, the better.

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