Debunking Three Common Scuba Diving Myths
Why Evidence Matters More Than Tradition
Scuba diving is built on safety, knowledge, and continuous learning. Equipment evolves, research improves, and training standards are regularly updated. Yet some pieces of advice continue to be repeated decade after decade, not because they are supported by modern evidence, but because instructors learned them from previous instructors.
Many divers can probably remember hearing statements such as:
- “Always turn the tank valve back a quarter turn.”
- “Follow the smallest bubbles during your ascent.”
- “Open your tank slowly or the pressure gauge glass can break.”
These recommendations have been passed from instructor to instructor for years. But are they still correct? Let’s take a closer look.
Myth 1: Always Turn the Tank Valve Back a Quarter Turn
This is probably one of the oldest myths still found in scuba diving.
Years ago, many valves required a slight turn back after fully opening because some older valve designs could become difficult to close if they were opened with excessive force. Turning the valve back slightly was intended to prevent the valve from binding.
Modern scuba valves are different.
Today’s valves are designed to be opened completely. Manufacturers generally recommend opening the valve fully until it stops naturally, without forcing it, and leaving it fully open.
Why is the quarter-turn dangerous?
Imagine the following situation:
A diver opens the valve, then turns it back a quarter turn.
Another buddy performs the pre-dive safety check and notices the valve is not fully open. Thinking they are helping, they turn it clockwise to “open it completely.” Unfortunately, they actually close the valve because it was already backed off.
The SPG may still show a full cylinder because there is pressure trapped in the regulator hoses. The diver starts the dive without realizing the tank valve is now closed.
The regulator continues to breathe normally for several breaths before suddenly becoming extremely difficult or impossible to breathe from.
This scenario has caused real diving incidents.
For this reason, many training organizations, equipment manufacturers, and dive safety experts now recommend opening the cylinder valve fully and leaving it fully open.
The best practice is simple:
- Open the valve completely.
- Do not force it once fully open.
- Confirm proper gas delivery by breathing from the regulator while watching the pressure gauge.
Modern equipment no longer requires the old quarter-turn practice.
Myth 2: Follow the Smallest Bubbles During Your Ascent
Many divers have heard:
“Just follow the smallest bubbles and your ascent rate will be correct.”
It sounds logical—but unfortunately, physics is more complicated.
Bubble speed depends on many factors besides your ascent rate.
These include:
- Bubble size
- Water currents
- Water movement
- Turbulence from exhalation
- Regulator exhaust design
- Depth
- Pressure changes
- Bubble merging
- Surface tension
- Buoyancy changes
- Drag forces
Small bubbles don’t always move the slowest
Tiny bubbles may remain attached to larger bubbles.
Some merge together into larger bubbles.
Others become trapped in eddies created by your body or equipment.
Water moving upward or downward can dramatically affect bubble speed.
Even your own exhalation changes how bubbles behave.
Pressure changes matter
As bubbles rise, the surrounding pressure decreases.
According to gas laws, the bubbles expand.
Larger bubbles become more buoyant and often accelerate as they approach the surface.
This means the same bubble does not travel at a constant speed throughout the ascent.
Bubble columns are unpredictable
Instead of one neat stream, divers create an entire column of bubbles.
Some bubbles rise faster.
Others collide.
Others merge.
Some spiral.
Some are pulled sideways by current.
Watching “the smallest bubble” is therefore highly subjective.
Which smallest bubble?
The one nearest your mask?
The one behind your shoulder?
The one affected by another diver?
There simply is no scientifically reliable bubble that represents a safe ascent speed.
What should divers do instead?
Modern dive computers continuously calculate ascent rate using pressure sensors.
They provide a much more accurate indication than observing bubbles.
Good buoyancy control, proper trim, and monitoring your dive computer are far more reliable ways to maintain a safe ascent.
Bubbles can provide a rough visual reference that you are moving upward, but they should never replace your ascent rate indicator.
Myth 3: Opening the Tank Quickly Can Break the Pressure Gauge Glass
Another myth still heard in some dive briefings is:
“Open the cylinder very slowly or the glass of the pressure gauge may break.”
There is little evidence that properly functioning scuba pressure gauges fail this way.
Modern submersible pressure gauges are specifically designed to withstand the operating pressures of scuba equipment.
When the cylinder valve opens, the pressure inside the high-pressure hose and gauge increases rapidly—but this pressure is internal and distributed throughout the system. The glass itself is not suddenly exposed to an uneven force that would normally cause it to shatter.
If an SPG window breaks while opening a cylinder, it is almost always because something else is already wrong, such as:
- A damaged gauge
- Manufacturing defects
- Severe corrosion
- Previous impact damage
- Poor maintenance
Opening the valve at a normal, controlled pace is perfectly acceptable.
The greater concern is not protecting the gauge glass—it is protecting the first-stage regulator from unnecessary stress caused by a rapid pressure surge.
Many modern regulators are designed to handle this without issue, but opening the valve smoothly and steadily remains good practice for overall equipment care.
The key point is this:
Opening a scuba cylinder normally does not cause a healthy pressure gauge window to explode.
Why Do These Myths Continue?
Scuba diving has a proud tradition of mentorship. Instructors learn from instructors, who learned from instructors before them.
That tradition is one of diving’s greatest strengths—but it can also allow outdated information to survive long after equipment and knowledge have changed.
Many myths persist simply because:
- “That’s how I was taught.”
- “Everyone does it.”
- “We’ve always done it this way.”
None of these are scientific evidence.
The diving industry has changed enormously over the last few decades. Regulators are more advanced. Cylinder valves have improved. Dive computers have replaced many older techniques. Research into diving physiology and equipment continues every year.
Good instructors continue learning throughout their careers and are willing to question long-standing habits when better evidence becomes available.
Modern Diving Requires Modern Thinking
Safe diving does not mean rejecting tradition—it means understanding why procedures exist and whether they are still relevant.
The best instructors are lifelong students. They read manufacturer recommendations, follow updates from training agencies, stay informed about equipment developments, and adapt their teaching when new evidence becomes available.
At Oceans 5 Gili Air, we believe scuba education should be based on current best practices, critical thinking, and an understanding of the science behind diving. Rather than simply repeating what has always been said, we encourage divers to ask questions, understand the reasons behind procedures, and continue learning throughout their diving journey.
Because in scuba diving, the safest tradition is never to stop learning.