6.3 - Fire Explosion and Decomposition Hazards

Module: Safety Leak Detection Shipping and Safe Disposal
Safety and technical verification date: August 10, 2026
Primary safety basis: Current EPA Section 608 test topics, current OSHA fire/explosion safety principles, current ASHRAE refrigerant-safety information, NIOSH technical guidance, and current refrigerant-manufacturer safety information
Course role: Explains why oxygen and compressed air must not be used for refrigerant-system leak testing, why refrigerant-air mixtures under pressure can become dangerous, how flames and hot surfaces can create ignition or decomposition hazards, and how technicians control ignition sources when working with flammable refrigerants

Learning Objectives

After completing this section, a student should be able to:

1. Explain why oxygen and compressed air must not be used for refrigerant-system leak testing or pressure testing.
2. Explain how some refrigerant-air mixtures can become combustible or otherwise hazardous, especially when pressure and concentration differ from normal atmospheric conditions.
3. Distinguish a refrigerant’s flammability hazard from its thermal-decomposition hazard.
4. Explain why an open flame or sufficiently hot surface can be dangerous even when the refrigerant involved is classified as nonflammable under normal test conditions.
5. Identify the general types of hazardous decomposition products that may form when halogenated refrigerants are exposed to high temperatures.
6. Explain why the exact decomposition products depend on the refrigerant’s chemical composition.
7. Recognize that modern refrigerants include nonflammable, lower-flammability, and higher-flammability products and that service procedures must match the refrigerant.
8. Identify common ignition sources that must be controlled when servicing equipment containing a flammable refrigerant.
9. Explain why refrigerant recovery, ventilation, leak checking, and manufacturer-approved service procedures must occur before hot work.
10. Apply a safe decision process to fire, explosion, and decomposition-hazard scenarios likely to appear on an EPA Section 608 examination.

Introduction

Refrigerants are selected partly because they can operate safely and reliably within refrigeration and air-conditioning systems. However, their behavior can change when they are:

• Mixed with air.
• Pressurized.
• Exposed to oxygen.
• Exposed to an open flame.
• Exposed to a sufficiently hot surface.
• Released near an ignition source.
• Heated in a closed container or component.
• Used in equipment or service tools not intended for their safety classification.

A common mistake is to divide refrigerants into only two categories:

flammable
or
nonflammable

and then assume that a refrigerant described as nonflammable creates no fire-related hazard.

That conclusion is unsafe.

Several different mechanisms must be considered:

Refrigerant + air + pressure
→ possible combustible or reactive mixture

Flammable refrigerant + air + ignition source
→ fire or flame propagation

Halogenated refrigerant + high temperature
→ thermal decomposition
→ toxic and corrosive decomposition products

The EPA Section 608 test-topic outline specifically expects technicians to know:

• To use nitrogen rather than oxygen or compressed air for leak detection.
• To use a pressure regulator and relief valve with nitrogen.
• That refrigerants can form decomposition products at high temperatures.

This section develops the reasoning behind those safety rules.

Detailed nitrogen pressure-test equipment and procedure are reserved for Section 6.5 - Nitrogen Pressure Testing.

Detailed refrigerant toxicity and flammability classifications are reserved for Section 6.4 - Refrigerant Safety Classifications.

Key Concepts

1. Never Use Oxygen for Refrigerant-System Leak Testing

Oxygen is a strong oxidizer.

Introducing oxygen into a refrigeration system can create a serious fire or explosion hazard when oxygen contacts:

• Refrigeration oil.
• Compressor oil.
• Organic residues.
• Some refrigerants.
• Other combustible materials.

The basic hazard relationship is:

Fuel or combustible material
+
high oxygen concentration
+
ignition / sufficient energy
→ rapid combustion

A refrigeration system contains materials that are not intended to be exposed to concentrated oxygen under test pressure.

For EPA 608 examination preparation:

Use dry nitrogen—not oxygen—for pressure-assisted refrigerant leak testing.

This is a safety rule, not merely a preference for better test accuracy.

2. Do Not Use Compressed Air for Refrigerant Leak Testing

Compressed air contains oxygen.

Using compressed air can introduce:

• Oxygen.
• Moisture.
• Other atmospheric contaminants.

More importantly for this section, a refrigerant mixed with air under elevated pressure can behave differently from the refrigerant alone under normal atmospheric test conditions.

Manufacturer safety guidance for multiple fluorinated refrigerants warns against using refrigerant-air mixtures for leak testing because such mixtures can become combustible.

Therefore:

Compressed air
→ introduces oxygen-containing air
→ can create unsafe refrigerant-air mixtures
→ must not replace dry nitrogen for refrigerant-system pressure testing

Dry nitrogen is used because it is inert under normal refrigeration service conditions and does not introduce oxygen or moisture in the way compressed air does.

The regulator, relief valve, pressure limit, and complete nitrogen test setup are covered in Section 6.5.

3. “Nonflammable Refrigerant” Does Not Mean “Safe to Mix With Air Under Pressure”

A refrigerant’s safety classification is determined under defined test conditions.

That classification should not be interpreted as permission to:

• Mix the refrigerant with compressed air.
• Pressurize a refrigerant-air mixture.
• Expose the mixture to an ignition source.
• Ignore manufacturer warnings.

Some refrigerants that are not flammable under ordinary classification test conditions can form combustible mixtures with air under unusual combinations of:

• Pressure.
• Temperature.
• Refrigerant concentration.
• Oxygen concentration.

This is one reason the service rule is simple:

Do not pressure-test a refrigerant system with oxygen or compressed air.
Use dry nitrogen with the required pressure controls.

4. Flammability and Thermal Decomposition Are Different Hazards

These two concepts are commonly confused.

Flammability

A flammable refrigerant can support flame propagation under specified conditions when:

• Refrigerant concentration is within a flammable range.
• Sufficient oxidizer is present.
• A suitable ignition source is present.

Conceptually:

Flammable refrigerant concentration
+
air / oxygen
+
ignition source
→ ignition may occur

Thermal Decomposition

A refrigerant does not have to sustain a flame to undergo thermal decomposition.

A sufficiently high temperature can break refrigerant molecules into other chemical species.

Conceptually:

Refrigerant
+
high temperature
→ chemical decomposition
→ hazardous decomposition products

Therefore:

A refrigerant can be classified as nonflammable and still produce dangerous decomposition products when exposed to flame or very hot surfaces.

5. Open Flames Create More Than One Hazard

An open flame can create:

1. An ignition hazard when a flammable refrigerant-air mixture is present.
2. A thermal-decomposition hazard when a halogenated refrigerant contacts the flame or sufficiently hot combustion zone.
3. An ignition source for oil, insulation, residue, or another combustible material.
4. A heat source that raises pressure in a closed component or cylinder.

The technician must therefore not think only about whether “the refrigerant burns.”

The more complete question is:

What can the flame ignite?
What can the flame decompose?
What pressurized object can the flame heat?

6. Hot Surfaces Can Also Create Hazard

A visible flame is not required for every ignition or decomposition event.

Potential high-temperature sources include:

• Brazing torches.
• Welding arcs and adjacent hot metal.
• Electric resistance heaters.
• Furnace or boiler surfaces.
• Engine exhaust components.
• Hot compressor surfaces under abnormal conditions.
• Grinding or cutting operations that create hot particles.
• Electrical faults.

Whether a particular surface can ignite a particular refrigerant mixture depends on:

• Refrigerant.
• Concentration.
• Surface temperature.
• Exposure time.
• Air movement.
• Pressure.
• Test method.
• Equipment configuration.

Do not memorize one universal “hot-surface ignition temperature” for all refrigerants.

Use current refrigerant-specific safety information and equipment instructions.

7. High Temperature Can Decompose Halogenated Refrigerants

Many common fluorinated or chlorinated refrigerants are halogenated compounds.

When they are exposed to sufficiently high temperatures, they can decompose into substances that are much more hazardous than the original refrigerant.

Depending on the refrigerant chemistry and conditions, decomposition products can include:

• Hydrogen fluoride (HF) from fluorine-containing compounds.
• Hydrogen chloride (HCl) from chlorine-containing compounds.
• Carbonyl fluoride or related carbonyl halides from some fluorinated compounds.
• Phosgene (COCl₂) or other chlorine-containing decomposition products under some conditions involving chlorine-containing halocarbons.

The exact list is refrigerant-specific.

The correct teaching rule is:

High-temperature decomposition products depend on the refrigerant’s chemical composition and must be checked in the current SDS.

Do not memorize “phosgene” as the universal decomposition product of every modern refrigerant.

8. Hydrogen Fluoride Is a Serious Decomposition Hazard

Fluorinated refrigerants can produce hydrogen fluoride under thermal decomposition conditions.

Hydrogen fluoride is highly hazardous and can:

• Irritate or damage the respiratory tract.
• Injure eyes.
• Injure skin.
• Produce serious systemic effects after significant exposure.

Therefore, a refrigerant flame or hot-work exposure should never be treated as harmless simply because the original refrigerant has relatively low acute toxicity.

If thermal decomposition is suspected:

Stop exposure if this can be done safely
→ leave the contaminated area
→ prevent additional exposure
→ ventilate according to the emergency procedure
→ obtain appropriate medical / emergency assistance
→ provide the refrigerant identity and SDS

Do not remain in the area to identify decomposition products by odor.

9. Phosgene Is Not a Universal Refrigerant Decomposition Product

Older HVAC training materials often strongly associate refrigerant and flame exposure with phosgene.

That historical warning is useful for some chlorine-containing halocarbons, but it can be misleading when generalized to every refrigerant.

A more accurate approach is:

Chlorine-containing halocarbon
+ high temperature
→ chlorine-containing decomposition products may form
→ phosgene can be a concern under some conditions

but:

Every refrigerant
+ flame
→ phosgene

is not correct.

Modern fluorinated refrigerants without chlorine may instead produce products such as:

• Hydrogen fluoride.
• Carbonyl fluoride.
• Other fluorinated decomposition products.

Always use the specific SDS.

10. Decomposition Products Can Be Toxic and Corrosive

Hazardous decomposition products are not only inhalation hazards.

They may also be:

• Corrosive to tissue.
• Corrosive to metals or equipment.
• Irritating to eyes.
• Irritating to the respiratory tract.
• Dangerous at concentrations much lower than the original refrigerant concentration involved.

This means that a small amount of refrigerant passing through a flame or high-temperature zone can create a serious local hazard.

A pungent or irritating odor after a refrigerant contacts a hot surface is a warning to leave the area—not a method for identifying the chemical.

Technical and Safety Details

1. Why Oxygen Increases Fire Severity

Combustion requires an oxidizer.

Ordinary air contains approximately 21% oxygen, but pure oxygen produces a much more strongly oxidizing environment.

Materials that burn slowly in air can burn:

• Faster.
• Hotter.
• More violently.

in oxygen-enriched conditions.

Introducing oxygen into refrigeration equipment therefore creates an unnecessary and severe hazard.

The safe service principle is:

Oxygen cylinder
→ never use as refrigerant-system test gas

2. Why Compressed Air Is Also Unsafe

A common incorrect thought is:

Pure oxygen is dangerous
but
shop air is mostly nitrogen
therefore compressed air is safe

This reasoning fails because compressed air still contains oxygen.

It can also contain:

• Moisture.
• Oil aerosol from some compressors.
• Particulates or contaminants.

A high-pressure refrigerant-air mixture may have a combustion behavior that differs from the refrigerant under normal conditions.

For leak testing:

Compressed air
→ wrong test gas

Dry nitrogen
→ correct general test gas
→ when used with regulator, pressure control, and equipment limits

3. Refrigerant-Air Mixture Hazard

Three variables matter greatly:

• Composition — how much refrigerant and air are mixed.
• Pressure — the total pressure of the mixture.
• Temperature — the thermal condition of the mixture.

A refrigerant manufacturer’s warning about combustible refrigerant-air mixtures is therefore not contradicted merely because the refrigerant has a nonflammable classification under a different standardized condition.

This distinction is important for examination questions.

A question may describe:

• A normally nonflammable refrigerant.
• A technician adding compressed air.
• A high-pressure system.

The correct safety conclusion remains:

Do not use compressed air; use dry nitrogen with proper pressure controls.

4. Fire Triangle Applied to Flammable Refrigerants

For a flammable refrigerant fire, three elements generally must coincide:

Fuel
→ refrigerant within an ignitable concentration range

Oxidizer
→ normally oxygen in air

Ignition source
→ flame, spark, arc, sufficiently energetic hot surface, or other capable source

Removing or controlling one element reduces the chance of ignition.

In refrigeration service, technicians often control the hazard by:

• Preventing refrigerant release.
• Recovering refrigerant before opening or hot work.
• Ventilating the work area.
• Verifying the atmosphere when required.
• Eliminating ignition sources.
• Using tools and service equipment appropriate to the refrigerant.
• Following manufacturer and code requirements.

5. Lower and Upper Flammability Limits

A flammable refrigerant does not burn at every concentration in air.

There is generally a concentration range within which flame propagation can occur.

The lower boundary is commonly called a:

• Lower flammability limit (LFL), or
• Lower explosive limit (LEL) in some contexts.

The upper boundary may be called a:

• Upper flammability limit (UFL), or
• Upper explosive limit (UEL).

For teaching purposes:

Below LFL
→ mixture is too lean to propagate flame under the specified test condition

Between LFL and UFL
→ flammable range under the specified test condition

Above UFL
→ mixture is too rich to propagate flame under the specified test condition

However, a technician must not intentionally create a rich mixture as a safety strategy.

Air can enter later and move the mixture into the flammable range.

No universal LFL or UFL value applies to all refrigerants.

6. A2L Does Not Mean “Nonflammable”

Modern HVAC equipment increasingly uses refrigerants classified in Class 2L.

The detailed classification system is covered in Section 6.4, but one distinction is essential here:

A2L
→ lower flammability
≠
nonflammable

An A2L refrigerant can ignite under suitable conditions.

Compared with higher-flammability refrigerants, ignition and flame propagation characteristics differ, but the technician must still:

• Control ignition sources.
• Use approved equipment.
• Follow charge and installation limits.
• Follow manufacturer instructions.
• Follow applicable codes and standards.

Do not use the informal phrase “basically nonflammable.”

7. Higher-Flammability Refrigerants Require Stronger Ignition Control

Some refrigerants, including certain hydrocarbons, have higher flammability.

Examples include refrigerants in ASHRAE Class 3.

Service procedures can require:

• Refrigerant-specific tools.
• Ventilation.
• Controlled work zones.
• Elimination of ignition sources.
• Limits on refrigerant charge.
• Specific recovery procedures.
• Equipment specifically designed for that refrigerant.

The technician must identify the refrigerant before service.

Do not infer the flammability classification only from:

• Cylinder color.
• Equipment size.
• Refrigerant number.
• Whether the system is residential or commercial.

Use:

• Nameplate.
• Refrigerant label.
• SDS.
• Manufacturer documentation.
• Current safety classification.

8. Ignition Sources

Potential ignition sources include:

• Open flames.
• Cigarettes or smoking materials.
• Torches.
• Welding.
• Electrical arcs.
• Switch contacts.
• Relays.
• Motors not suitable for the refrigerant application.
• Static discharge under some conditions.
• Grinding sparks.
• Hot surfaces capable of ignition under the actual conditions.

Not every electrical component automatically ignites every flammable refrigerant mixture.

The correct question is whether the source has enough energy or temperature to ignite the specific refrigerant-air mixture under the actual conditions.

9. Service Equipment Must Match the Refrigerant

Recovery machines, vacuum pumps, leak detectors, and other service tools may contain:

• Motors.
• Switches.
• Relays.
• Electrical contacts.

When a flammable refrigerant is involved, service equipment must be suitable for that refrigerant and service application.

Do not assume:

Worked with R-410A
→ automatically suitable for R-32, R-454B, R-290, or another flammable refrigerant

Equipment compatibility and certification were introduced in Section 5.3 - Recovery Equipment Certification and Service Fittings.

10. Hot Work Requires Control of Refrigerant

Hot work can include:

• Brazing.
• Soldering.
• Welding.
• Cutting.
• Grinding.

Before performing hot work on refrigerant-containing equipment:

• Identify the refrigerant.
• Follow the equipment manufacturer’s service procedure.
• Properly recover refrigerant from the portion being opened as required.
• Isolate the work area appropriately.
• Verify that a flammable refrigerant release will not create an ignitable atmosphere.
• Provide ventilation as required.
• Control ignition sources outside the intended hot-work point.
• Follow applicable fire-prevention and hot-work procedures.

A torch must not be used as a refrigerant leak detector.

11. Do Not Heat Refrigerant Cylinders With an Open Flame

A refrigerant cylinder is a pressure vessel.

Heating a closed cylinder raises the temperature of its contents and normally increases internal pressure.

An open flame creates two hazards:

1. Local overheating and pressure rise.
2. Fire or decomposition hazard if refrigerant is released.

Therefore:

Open flame
→ never use to heat a refrigerant cylinder

Cylinder heating, transportation, and exposure to environmental heat are discussed further in Section 6.8 - Cylinder Shipping and Transportation.

12. Pressure Relief Is Not Permission to Overheat Equipment

Pressure-relief devices are emergency protective devices.

They do not make it acceptable to:

• Exceed equipment pressure limits.
• Expose cylinders to flame.
• Block relief paths.
• Heat a closed system carelessly.
• Intentionally drive a system to relief pressure.

The preferred safety sequence is:

Prevent abnormal pressure
→ remain within rated limits
→ maintain required relief protection

not:

Overpressure system
→ depend on relief valve

Thermal Decomposition in More Detail

1. What Thermal Decomposition Means

A refrigerant molecule contains chemical bonds.

When enough thermal energy is supplied, those bonds can break and the refrigerant can react to form new compounds.

The process is not the same as ordinary boiling.

Boiling
→ phase change
→ chemical identity remains refrigerant

Thermal decomposition
→ chemical reaction
→ new chemical species form

This distinction matters.

A refrigerant vapor passing near a torch may remain a vapor physically but also undergo chemical decomposition chemically.

2. Sources of Decomposition Temperature

Potential decomposition sources include:

• Torch flame.
• Welding arc.
• Very hot metal.
• Combustion chamber.
• Electric arc.
• Fire involving refrigeration equipment.

The exact temperature required and resulting products are refrigerant-specific.

3. Fluorine-Containing Refrigerants

Many modern refrigerants contain fluorine.

High-temperature decomposition may form:

• Hydrogen fluoride.
• Carbonyl fluoride.
• Other fluorinated products.

Hydrogen fluoride is particularly important because it is corrosive and toxic.

The SDS for the actual refrigerant should be reviewed before hot work.

4. Chlorine-Containing Refrigerants

CFC and HCFC refrigerants contain chlorine.

Under severe heating, chlorine-containing decomposition products can form.

Depending on conditions, these may include:

• Hydrogen chloride.
• Carbonyl chloride compounds.
• Phosgene.

For exam preparation, the important relationship is:

Chlorinated refrigerant
+
high heat / flame
→ toxic and corrosive decomposition products can form

Do not intentionally smell the products to identify them.

5. Refrigerant Fire Can Produce Additional Products

If a flammable refrigerant actually burns, the products depend on:

• Refrigerant chemistry.
• Oxygen concentration.
• Flame temperature.
• Completeness of combustion.
• Other materials burning nearby.

A real equipment fire can therefore produce a complex smoke and gas mixture.

Emergency response is not based on identifying one gas by memory.

Instead:

Evacuate / isolate
→ use trained emergency response
→ use appropriate respiratory protection
→ provide refrigerant and SDS information

Ignition-Source Control

1. Before Service

Before servicing equipment containing a refrigerant with flammability concerns:

1. Identify the refrigerant from reliable sources.
2. Review the SDS.
3. Review the equipment manufacturer’s instructions.
4. Determine the refrigerant’s current safety classification.
5. Determine whether special service tools are required.
6. Confirm ventilation requirements.
7. Identify ignition sources in and near the work area.
8. Control or remove those ignition sources as required.
9. Follow the approved recovery and service procedure.

2. During Service

During the task:

• Prevent unnecessary refrigerant release.
• Maintain required ventilation.
• Keep the work area controlled.
• Keep unauthorized people away when required.
• Do not smoke.
• Do not introduce oxygen or compressed air into the system.
• Use suitable leak-detection methods.
• Use service equipment appropriate to the refrigerant.
• Monitor the area when required by the procedure or code.
• Stop if an unexpected release occurs.

3. After an Unexpected Release

If a flammable refrigerant is unexpectedly released:

Stop work
→ avoid operating potential ignition sources if doing so could create a spark
→ evacuate as required
→ follow emergency procedure
→ ventilate safely
→ verify atmosphere when required
→ correct leak before returning equipment to service

The exact sequence must follow the product, equipment, and facility emergency procedures.

4. Do Not Create a Spark While Responding to a Leak

A subtle hazard is that operating an ordinary electrical switch can create a small arc.

If a flammable mixture may already be present, the technician should not automatically:

• Turn lights on.
• Turn lights off.
• Plug in ordinary equipment.
• Unplug energized equipment.
• Operate non-rated fans.

unless the emergency procedure establishes that the equipment is safe for the environment.

Use equipment appropriate to the refrigerant and hazard classification.

Safety Scenario Comparisons

Important Terms

Combustible Mixture

A gas or vapor mixture capable of burning under specified conditions.

For refrigeration service, some refrigerant-air mixtures can become combustible under conditions different from the standard classification condition.

Compressed Air

Atmospheric air raised to a pressure above ambient pressure.

Compressed air contains oxygen and must not be used as the pressure-test gas for a refrigerant circuit.

Decomposition Product

A new chemical substance formed when a chemical breaks down because of heat, reaction, radiation, or another mechanism.

Flammability

The ability of a substance to ignite and propagate flame under specified conditions.

Flammable Range

The concentration range in which a fuel-air mixture can propagate flame under specified conditions.

The lower and upper limits are refrigerant-specific.

Hydrogen Fluoride

A highly hazardous fluorine-containing compound that can form during thermal decomposition of some fluorinated refrigerants.

Hydrogen Chloride

A corrosive chlorine-containing compound that can form during thermal decomposition of some chlorine-containing refrigerants.

Ignition Source

A flame, spark, electrical arc, hot surface, or other energy source capable of igniting a specific combustible mixture under the conditions present.

Lower Flammability Limit (LFL)

The lower concentration boundary at which a refrigerant-air mixture can propagate flame under the specified test conditions.

Oxygen

A strong oxidizer required for ordinary combustion.

Pure oxygen must not be used for refrigeration-system leak or pressure testing.

Phosgene

A highly toxic chlorine-containing compound that can be produced under some high-temperature decomposition conditions involving chlorine-containing halocarbons.

Phosgene is not a universal decomposition product of every refrigerant.

Thermal Decomposition

Chemical breakdown caused by high temperature.

Thermal decomposition changes the chemical identity of the refrigerant and can create toxic or corrosive products.

EPA 608 Exam Focus

What Students Must Remember

EPA’s current Section 608 test topics explicitly include:

Use nitrogen
rather than
oxygen or compressed air
for leak detection

and:

Use a pressure regulator
and relief valve
with nitrogen

EPA also includes:

Decomposition products of refrigerants
at high temperatures

as a Type I safety topic.

High-Priority Safety Rules

OXYGEN
→ never use for refrigerant-system leak testing

COMPRESSED AIR
→ do not use for refrigerant-system leak testing

DRY NITROGEN
→ proper general pressure-test gas
→ use regulator and required pressure protection

REFRIGERANT + HIGH HEAT
→ possible toxic / corrosive decomposition products

FLAMMABLE REFRIGERANT + AIR + IGNITION SOURCE
→ possible fire

High-Priority Distinctions

Likely Question Patterns

Students may be asked:

• Which gas should be used instead of oxygen or compressed air for leak testing.
• Why oxygen must not be introduced into a refrigeration system.
• Why compressed air is unsafe as a refrigerant leak-test gas.
• Whether a nonflammable refrigerant can create a hazard when mixed with air under pressure.
• What can happen when refrigerant contacts an open flame or high-temperature surface.
• Whether every refrigerant produces phosgene.
• Whether A2L means nonflammable.
• Why ignition sources must be controlled during flammable-refrigerant service.
• Why a refrigerant cylinder must not be heated with an open flame.
• What information should be checked before hot work on refrigerant equipment.

Common Mistakes and Confusing Points

Mistake 1: Using Oxygen Because It Is “Dry”

Oxygen may be dry, but it is a strong oxidizer.

It must not be used as a refrigerant-system pressure-test gas.

Mistake 2: Assuming Shop Air Is Safe Because It Contains Mostly Nitrogen

Compressed air still contains oxygen and moisture.

Use dry nitrogen.

Mistake 3: Assuming a Nonflammable Refrigerant Can Be Safely Mixed With Air Under Pressure

Manufacturer safety information warns that refrigerant-air mixtures can become combustible under certain pressure and concentration conditions.

Do not create the mixture.

Mistake 4: Treating Every Fire-Related Hazard as Flammability

A nonflammable refrigerant may still thermally decompose near a flame or hot surface.

Mistake 5: Treating A2L as Equivalent to A1

A2L refrigerants have lower flammability characteristics, but they are not nonflammable.

The classification system is developed in Section 6.4.

Mistake 6: Assuming Every Electrical Device Is an Ignition Source in Every Situation

Ignition depends on the energy source, refrigerant, concentration, and actual conditions.

Use equipment suitable for the refrigerant and follow manufacturer/code requirements.

Mistake 7: Using a Torch to Search for Refrigerant Leaks

A torch can:

• Ignite a flammable mixture.
• Decompose halogenated refrigerant.
• Create hazardous gases.

Use an appropriate leak-detection method.

Mistake 8: Memorizing “Phosgene” as the Only Decomposition Product

Modern fluorinated refrigerants can produce hydrogen fluoride and other fluorinated decomposition products.

Chlorine-containing refrigerants can produce different chlorine-containing products.

Check the SDS.

Mistake 9: Assuming Refrigerant Boiling Is Decomposition

Boiling is a physical phase change.

Thermal decomposition is a chemical change.

Mistake 10: Heating a Recovery Cylinder With a Flame to Increase Pressure

This can dangerously overheat a pressure vessel and create additional fire or decomposition hazards.

Mistake 11: Depending on a Relief Valve Instead of Controlling Pressure

A relief valve is a last protective layer.

Do not intentionally exceed the rated pressure of the system or cylinder.

Mistake 12: Continuing Hot Work After an Unexpected Refrigerant Release

Stop the work, control the area, follow the emergency procedure, ventilate, and verify safe conditions before restarting.

Concept-Check Questions

Question 6.3-1

Which gas should generally be used to pressurize a refrigeration system for leak testing?

A. Pure oxygen

B. Compressed shop air

C. Dry nitrogen used with proper pressure controls

D. Refrigerant mixed with oxygen

Question 6.3-2

Why must oxygen not be used to pressure-test a refrigeration system?

A. Oxygen always freezes refrigerant oil.

B. Oxygen is a strong oxidizer and can create a severe fire or explosion hazard with combustible materials in the system.

C. Oxygen prevents gauges from measuring pressure.

D. Oxygen is chemically identical to nitrogen.

Question 6.3-3

Why is compressed air not an acceptable substitute for dry nitrogen when pressure-testing a refrigerant circuit?

A. Compressed air contains oxygen and moisture and can contribute to hazardous refrigerant-air mixtures.

B. Compressed air cannot be pressurized above atmospheric pressure.

C. Compressed air contains no nitrogen.

D. Compressed air always condenses into liquid inside the system.

Question 6.3-4

Which statement best distinguishes refrigerant flammability from thermal decomposition?

A. They are two names for the same process.

B. Flammability requires the refrigerant to freeze, while decomposition requires it to boil.

C. Flammability concerns ignition and flame propagation, while thermal decomposition is chemical breakdown caused by high temperature.

D. Decomposition occurs only in hydrocarbon refrigerants.

Question 6.3-5

Which statement about high-temperature decomposition products is most accurate?

A. Every refrigerant produces only phosgene.

B. Refrigerants never form hazardous products unless they are classified as flammable.

C. The decomposition products depend on the refrigerant chemistry; fluorinated and chlorinated refrigerants can form different toxic or corrosive products.

D. Thermal decomposition changes only the physical state of the refrigerant.

Question 6.3-6

Which statement about an A2L refrigerant is correct?

A. A2L means the refrigerant cannot burn under any condition.

B. A2L indicates lower flammability characteristics, but ignition-source control is still required.

C. A2L means the refrigerant is pure oxygen.

D. A2L equipment may always be serviced with tools intended only for nonflammable refrigerants.

Question 6.3-7

A technician is preparing to braze a refrigerant line. Which approach is safest?

A. Leave refrigerant in the line so the technician can smell a leak.

B. Add compressed air so the line stays pressurized during brazing.

C. Follow the manufacturer and applicable service procedure, properly manage the refrigerant before opening or hot work, ventilate as required, and control ignition hazards.

D. Heat the refrigerant cylinder with the torch to increase recovery speed.

Question 6.3-8

A pungent irritating gas is noticed after refrigerant vapor contacts a very hot surface. What should the technician assume?

A. The odor proves that the gas is harmless.

B. The refrigerant has simply changed from liquid to vapor.

C. Hazardous thermal-decomposition products may be present, so exposure should stop and the applicable emergency/SDS procedure should be followed.

D. The technician should move closer and identify the gas by smell.

Section Summary

The principal fire, explosion, and decomposition safety relationships are:

Oxygen
→ strong oxidizer
→ never use for refrigerant-system leak testing

Compressed air
→ contains oxygen and moisture
→ can contribute to unsafe refrigerant-air mixtures
→ do not use for refrigerant-system leak testing

Dry nitrogen
→ general pressure-test gas
→ requires regulator, pressure control, and relief protection

Flammable refrigerant
+
air
+
capable ignition source
→ fire can occur

Halogenated refrigerant
+
high temperature
→ thermal decomposition
→ toxic / corrosive products may form

The major points are:

• EPA expects technicians to use nitrogen rather than oxygen or compressed air for leak detection.
• Oxygen must never be used to pressure-test a refrigeration system.
• Compressed air is not an acceptable substitute for dry nitrogen.
• Refrigerant-air mixtures under pressure can create hazards even when the refrigerant is normally classified as nonflammable.
• Flammability and thermal decomposition are different.
• Open flames can ignite flammable refrigerant mixtures and decompose halogenated refrigerants.
• Hot surfaces can also create ignition or decomposition hazards.
• Fluorinated refrigerants can form hazardous fluorine-containing decomposition products such as hydrogen fluoride.
• Chlorine-containing refrigerants can form hazardous chlorine-containing products; phosgene can be a concern under some conditions.
• Do not treat phosgene as the universal decomposition product of every refrigerant.
• A2L refrigerants have lower flammability but are not nonflammable.
• Ignition sources must be controlled according to the refrigerant, equipment, manufacturer instructions, and applicable codes.
• Recovery and service equipment must be appropriate for the refrigerant.
• Never heat a refrigerant cylinder with an open flame.
• If an unexpected refrigerant release occurs during hot work, stop work and follow the emergency procedure before restarting.

The next section explains the toxicity and flammability classification system used to communicate these refrigerant safety characteristics.

See Section 6.4 - Refrigerant Safety Classifications.

References

Current EPA Examination Sources

1. U.S. Environmental Protection Agency, Test Topics — Section 608 Technician Certification, Core safety topics specifying use of nitrogen rather than oxygen or compressed air for leak detection, use of a pressure regulator and relief valve with nitrogen, and Type I safety topic covering decomposition products of refrigerants at high temperatures. Accessed August 10, 2026.

2. U.S. Environmental Protection Agency, Section 608 Technician Certification Requirements, current technician-certification framework. Accessed August 10, 2026.

Current Safety and Technical Sources

3. Occupational Safety and Health Administration, Oxygen-Enriched Atmospheres and Fire/Explosion Hazard, OSHA Technical Manual discussion that oxygen-enriched atmospheres increase fire and explosion hazards because ordinary combustible materials burn more rapidly. Accessed August 10, 2026.

4. National Institute for Occupational Safety and Health, Health Hazard Evaluation Report 80-87-708, discussion that open flames and hot surfaces can thermally decompose halogenated hydrocarbons into toxic and corrosive substances including hydrogen chloride and hydrogen fluoride. Current CDC/NIOSH archive accessed August 10, 2026.

5. Centers for Disease Control and Prevention, Hydrogen Fluoride — Chemical Emergencies, health hazards associated with hydrogen fluoride exposure. Accessed August 10, 2026.

Refrigerant-Safety and Manufacturer Sources

6. Chemours, Opteon™ XP10 Retrofit Guidelines, warning not to use refrigerant-air mixtures for leak checking because such mixtures can become combustible; use dry nitrogen without exceeding the system design maximum pressure. Accessed August 10, 2026.

7. Chemours, Opteon™ XP40 Retrofit Guidelines, warning not to use refrigerant-air mixtures for leak testing and direction to use dry nitrogen within the system design pressure. Accessed August 10, 2026.

8. Chemours, Safety of Opteon™ XL Refrigerants, safety guidance for lower-flammability A2L refrigerants, ventilation, leak response, oxygen monitoring, and use of service equipment suitable for A2L refrigerants. Accessed August 10, 2026.

9. Honeywell, HFC-227ea Safety Data Information, example manufacturer SDS information identifying strong heating, flame, sparks, compressed air, and oxygen among conditions/materials to avoid and identifying hydrogen fluoride and fluorophosgene as hazardous decomposition products. Accessed August 10, 2026.

Current Refrigerant-Classification Sources

10. ASHRAE, Refrigerant Designations, current public listing of refrigerant designations and safety classifications based on toxicity and flammability data. Accessed August 10, 2026.

11. ASHRAE, Refrigeration Resources, current description of Standard 34 refrigerant safety classification and Standard 15 refrigeration-system safety requirements. Accessed August 10, 2026.

Project Cross-References

12. Section 5.3 - Recovery Equipment Certification and Service Fittings.

13. Section 6.1 - Personal Protective Equipment and Refrigerant Exposure.

14. Section 6.2 - Respiratory and Confined-Space Hazards.

15. Section 6.4 - Refrigerant Safety Classifications.

16. Section 6.5 - Nitrogen Pressure Testing.

17. Section 6.8 - Cylinder Shipping and Transportation.