What You Breathe: Why Scuba Air Quality Matters More Than You Think
Paul Lenharr II Dec 21, 2025
What You Breathe: Why Scuba Air Quality Matters More Than You Think
One of the most common questions divers ask is why scuba air fills cost what they do.
The short answer involves compressors, maintenance, filtration, testing, and consumables. But the important answer isn’t about money at all—it’s about understanding what you’re breathing and why the quality of that air matters.
Anyone with enough money can buy a compressor capable of filling scuba cylinders. There are no laws preventing someone from owning or operating one, and there are no universal requirements that the air being produced is safe to breathe underwater.
What matters isn’t the compressor itself.
What matters is how it’s maintained—and who is responsible for it.
How a Scuba Compressor Works (At a High Level)
All scuba compressors operate on the same basic principle.
Ambient air is drawn in through an intake and passed through multiple compression stages. With each stage, pressure increases until the air reaches scuba-level pressure and is delivered into your tank.
On paper, this sounds simple.
In practice, producing clean, breathable, oxygen-compatible air is anything but.
Air Intake: Where Everything Starts
The air you breathe begins at the compressor intake.
If the intake draws contaminated air, that contamination doesn’t magically disappear—it gets compressed and concentrated.
This is especially critical for compressors powered by gas or diesel engines. Exhaust from these engines contains carbon monoxide (CO), a colorless, odorless gas that can be lethal underwater even in extremely small amounts.
Carbon monoxide behaves like any other gas:
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it obeys gas laws
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its partial pressure increases with depth
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it enters your bloodstream just like oxygen and nitrogen
A trace amount at the surface can become dangerous once compressed and breathed underwater.
Proper intake placement is critical. It must be located in a clean, well-ventilated area, far from exhaust, fumes, or contaminants.
Most compressors also use intake filters to remove dust and particulates. These filters do not remove carbon monoxide, but they protect the compressor and reduce particulate contamination.
At Southern Maryland Divers, our compressor intake is located in a clean, well-ventilated environment. It uses dual intake filtration, checked every 20 hours of compressor operation and replaced as needed—and monthly regardless of usage.
Compressor Oil: Heat, Oxygen, and Fire Risk
Compressing air generates heat. Without lubrication, compressors would destroy themselves.
However, lubrication introduces another concern: oil mist.
Even the best-maintained compressors pass microscopic amounts of oil into the air stream. While this is usually harmless for breathing air, it becomes critical when oxygen levels increase—as with nitrox.
Fire requires three things:
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Heat
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Oxygen
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Hydrocarbons
We cannot eliminate heat.
We cannot eliminate oxygen.
We can eliminate hydrocarbons.
Using synthetic, food-grade, oxygen-compatible oil removes hydrocarbons from the equation, dramatically reducing the risk of combustion and carbon monoxide production.
Petroleum-based oils can allow micro-combustion events—sometimes unnoticed—that create carbon monoxide and contaminate breathing gas.
Synthetic food-grade oil:
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contains no hydrocarbons
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reduces fire risk
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eliminates a key source of CO contamination
It also costs significantly more—often five times the cost of conventional oils.
Southern Maryland Divers uses only high-grade, food-grade synthetic oil specifically approved for oxygen-compatible air systems.
Post-Compression Filtration: Where Air Becomes Breathable
After compression, air passes through a filtration system. This is the most critical step in producing clean breathing gas.
High-quality scuba filtration removes:
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water vapor
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carbon monoxide
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hydrocarbons and oil mist
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odors and taste
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particulate matter
Advanced filters contain materials such as:
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activated carbon
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molecular sieve
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desiccants
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hopcalite
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silica gel
Together, these components ensure the air meets breathing-gas and oxygen-compatibility standards.
Filters are sealed from the factory and have a finite lifespan. Their effectiveness depends on:
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gas volume processed
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inlet air quality
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temperature
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filter size
Proper shops monitor filter life closely. Southern Maryland Divers checks filtration lifespan every 20 hours of compressor operation and replaces filters monthly regardless of remaining capacity.
We use Lawrence Factor filtration, widely recognized as the highest-grade scuba filtration available. These filters are expensive—but quality air is not where corners get cut.
How Do We Know the Air Is Safe?
Quality air isn’t assumed—it’s verified.
Reputable dive shops submit air samples for laboratory analysis at least quarterly. Samples are tested by certified facilities and evaluated against breathing-air standards.
Results are clearly marked PASS or FAIL, with measured values included.
A responsible shop is proud of these results.
Southern Maryland Divers posts current air quality results:
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at the compressor
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in-store
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and publicly on our website
Not because it’s required—but because transparency matters.
Take-Home Points
• You may find cheaper fills elsewhere, but you are the one breathing that air. Knowledge, training, and diligence matter.
• It is completely appropriate to ask to see air quality test results. Look for PASS and ensure testing is current.
• If a shop cannot or will not show results—walk away.
• Cheaper is not always better. Producing high-quality breathing gas costs money, effort, and expertise.
Air fills aren’t about profit.
They’re about trust. Even putting all that aside, we breathe the same gas you do when we dive!
And your health is worth protecting.