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Quizzes > Science

Acetylene gas not explosive: true or false?

Quick acetylene gas quiz on safety myths and facts. Instant results.

Editorial: Review CompletedCreated By: Josiah BuwaldaUpdated Aug 25, 2025
Difficulty: Moderate
2-5mins
Learning OutcomesCheat Sheet
Paper art welding scene with mask torch gloves acetylene cylinder safety symbols and first aid icons on sky blue background

This quiz helps you check facts about acetylene explosiveness, safe torch setup, and basic first aid. Practice spotting myths, get answers in seconds, and follow up with our acetylene safety quiz, fire safety true or false, and OSHA hazard communication quiz. It is quick and clear, so you can focus on safer work.

Acetylene has a wide flammability range in air.
False
True
Acetylene has a wide flammability range between 2.5% and 100% in air, making it highly flammable across many mixtures. This poses significant fire and explosion hazards if not handled properly. Proper ventilation and leak detection are essential.
Pure acetylene must not be compressed above 15 psi.
False
True
Acetylene gas is unstable and can decompose explosively when pressurized above 15 psi (104 kPa). To avoid decomposition, cylinders are filled with acetone and limited to this pressure. Regulators and lines must maintain safe pressure levels.
Acetylene forms explosive complexes with copper.
False
True
Acetylene forms highly explosive copper acetylide when it comes in contact with copper or copper-bearing alloys. This substance is shock-sensitive and can detonate. Hence, copper should be avoided in acetylene systems.
Acetylene is heavier than air.
False
True
The molar mass of acetylene is about 26 g/mol, which is slightly lighter than air (approximately 29 g/mol). As a result, acetylene tends to disperse upward, but proper ventilation is still required.
Acetylene gas smells like rotten garlic.
False
True
Acetylene is an odorless gas, so leaks cannot be detected by smell. Additives are not used because they can contaminate welding operations. Leak detection relies on proper methods such as soap solution or electronic gas detectors.
An acetylene cylinder should always be stored upright.
True
False
Acetylene cylinders must be stored upright to ensure the acetone and porous mass remain correctly situated inside. Upright storage prevents liquid acetone from entering regulators and flashback arrestors.
Welding goggles with shade 5 are sufficient for all acetylene welding tasks.
False
True
Shade 5 goggles may be insufficient for many oxyacetylene welding operations, which often require darker filters depending on the intensity and thickness of material. Always refer to ANSI Z87.1 standards for proper shade selection.
A flashback arrestor reduces the risk of flame traveling back into the gas lines.
False
True
Flashback arrestors contain a flame arrestor element and check valve that stop flame or reverse gas flow into supply lines, significantly reducing the risk of backfire and flashback incidents.
Acetylene leaks can be detected with soap solution.
False
True
A soap solution applied to fittings and connections will foam in the presence of a leak, making it a simple and effective method for detecting gas leaks in acetylene systems.
Grease should never be used on acetylene cylinder valves.
False
True
Oil and grease are reactive with acetylene and can form unstable compounds that may detonate. Never use lubricants on acetylene equipment.
Acetylene cylinder valves should be opened all the way to ensure a proper seal.
True
False
Cylinder valves should be turned fully open to ensure the seating surfaces engage properly, reducing wear and preventing leaks. Some operators back off a quarter turn for ease of shutoff after seating.
When changing acetylene cylinders, it's safe to use a leaking hand tight connector for a short time.
True
False
Using a leaking or hand-tight connector, even temporarily, risks gas release and potential ignition. Always repair or replace faulty fittings before resuming work.
Acetylene's autoignition temperature in air is about 305°C.
True
False
The autoignition temperature of acetylene in air is approximately 305°C, which is lower than many other fuels, increasing its fire hazard potential in hot environments.
Acetylene becomes unstable and may decompose explosively at pressures above 15 psi even without air.
True
False
Acetylene can decompose explosively without oxygen when pressurized above 15 psi due to its unstable triple-bond structure. The cylinder's acetone medium and pressure limit mitigate this risk.
In case of acetylene fire, using a carbon dioxide extinguisher is recommended.
False
True
Carbon dioxide extinguishers are not recommended for acetylene fires as they may not cool the acetylene below its ignition temperature; dry chemical or water spray extinguishers are preferred.
Acetylene reacts violently with chlorine.
True
False
Acetylene reacts violently with chlorine gas, forming explosive compounds that can cause rapid pressure increases and detonation.
Flashback arrestors must be placed on both torch handle and regulator.
False
True
Flashback arrestors should be installed at both the regulator outlet and the torch handle to provide dual protection against reverse flow and flashback incidents.
First aid for acetylene inhalation includes administering 100% oxygen.
False
True
First aid for inhalation exposure is to remove the person to fresh air and seek medical attention; administering 100% oxygen is a medical procedure rather than standard first aid.
It's safe to use acetylene near open electrical circuits.
False
True
Acetylene is highly flammable and should not be used near open electrical circuits due to the risk of sparks igniting the gas. Maintain proper clearance and grounding at all times.
Acetylene regulators should be tested for leaks with a combustible gas detector.
True
False
Combustible gas detectors provide a sensitive method for checking regulator and line leaks, improving safety over visual or soap methods alone.
In oxyacetylene welding, too little oxygen leads to a carburizing flame.
True
False
A carburizing flame results when the acetylene flow exceeds the oxygen, creating excess carbon and leading to a reducing flame often recognized by yellow sooty tips.
Always wear leather gloves when handling acetylene cylinders.
False
True
Leather gloves protect hands from mechanical injury, heat, and minor chemical exposure when handling cylinders; synthetic gloves may melt or catch fire.
Ventilation requirements for indoor acetylene use are similar to those for propane.
True
False
Acetylene requires stricter ventilation than propane due to its broader explosive range and toxicity; propane's heavier-than-air nature also impacts ventilation design differently.
Cylinder manifolds allow mixing acetylene and oxygen in a single line.
True
False
Cylinder manifolds must keep acetylene and oxygen lines separate until just before the torch tip to prevent dangerous pre-mixing and potential explosions in the lines.
Acetylene can decompose in the absence of oxygen if heated above 300°C under high pressure.
True
False
Without oxygen, acetylene can thermally decompose at high temperatures, especially above 300°C under pressure, potentially leading to explosive reactions due to its unstable triple bond.
A reverse flow check valve prevents gas from flowing from the torch into the supply lines.
False
True
A reverse flow check valve is designed to allow flow only in one direction, preventing gas from the torch from entering supply lines and reducing cross-contamination risk.
In an emergency acetylene shutoff, closing the oxygen valve first is best practice.
True
False
When shutting down an oxyacetylene torch in an emergency, the acetylene valve should be closed first to extinguish the flame; closing oxygen first risks creating a fuel-rich mixture and flashback.
Acetylene cylinders should be hydrotested every five years.
False
True
U.S. Department of Transportation regulations require acetylene cylinders to undergo hydrostatic testing every five years to ensure structural integrity and safe operation.
For acetylene leaking inside a confined space, entry without protective equipment is allowed if leak is small.
False
True
Entering a confined space with an acetylene leak, even a small one, is unsafe without proper respiratory protection and gas monitoring due to asphyxiation and explosion risks.
Acetylene's explosion limits in oxygen are wider than in air.
True
False
Acetylene has a wider flammability range in air (2.5 - 100%) than in pure oxygen, where its explosion limits narrow, although reactions are more vigorous.
Acetylene can polymerize on copper surfaces at room temperature.
True
False
Copper catalyzes acetylene polymerization at room temperature, forming unstable solids that pose explosion hazards; copper alloys should be avoided in acetylene systems.
A leaking acetylene cylinder should be moved to a well-ventilated area if safe.
False
True
If a cylinder develops a minor leak, moving it to a well-ventilated outdoor area while keeping it upright can reduce risk until qualified personnel repair it.
Acetylene poses both asphyxiation and fire hazards.
True
False
Acetylene can displace oxygen in confined spaces (asphyxiant) and ignite at low energies, making it both an asphyxiation and fire hazard.
Eye injuries from acetylene welding are best treated with cold water rinses for at least 15 minutes.
True
False
Eye exposure to welding arcs can cause heat burns or photokeratitis; immediate cold water rinsing for at least 15 minutes reduces damage and helps prepare for medical evaluation.
Acetylene is dissolved in acetone in the cylinder to increase gas capacity.
False
True
Acetylene is dissolved in acetone within a porous mass to stabilize the gas and increase storage capacity, allowing more gas to be held safely under pressure.
Arc welding near acetylene lines is safe if the cylinder valve is closed.
True
False
Even with the cylinder valve closed, residual acetylene in lines can ignite during arc welding; lines must be purged and disconnected to ensure safety.
The maximum recommended outlet pressure for an acetylene regulator in cutting operations is 1.5 bar.
False
True
Most standards recommend acetylene outlet pressures not exceed 1.5 bar (about 22 psi) to prevent gas decomposition and ensure stable flame control during cutting operations.
Oxygen should be shut off before acetylene when shutting down an oxyacetylene torch.
True
False
The acetylene valve should be closed first to extinguish the flame safely; shutting oxygen first risks a fuel-rich mixture that can flash back into the acetylene line.
Autoignition temperature of acetylene is lower than that of propane.
False
True
Acetylene has an autoignition temperature of around 305°C, which is lower than propane's approximately 470°C, making it more susceptible to ignite spontaneously.
When a regulator becomes clogged with acetylene, its seat should be cleaned with oil.
False
True
Oil or grease must never be used on acetylene regulators or fittings; they can react to form unstable compounds and cause explosions.
0
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Study Outcomes

  1. Understand Acetylene Gas Risks -

    Understand the combustible nature of acetylene gas and correctly determine whether statements like "acetylene gas is not explosive" are true or false.

  2. Apply Oxygen-Acetylene Welding Protocols -

    Apply standardized safety measures when setting up and operating oxygen-acetylene welding equipment, including proper gear selection and leak checks.

  3. Identify and Administer First Aid for Welding Burns -

    Identify various welding burn injuries and perform immediate first aid steps to minimize damage and promote safe recovery.

  4. Analyze Welding Safety True/False Scenarios -

    Analyze a series of welding safety true/false questions to reinforce critical thinking and hazard recognition skills in real-world situations.

  5. Demonstrate Emergency Response for Gas Leaks -

    Demonstrate the appropriate emergency procedures to handle acetylene gas leaks, ensuring swift and safe resolution of potential hazards.

Cheat Sheet

  1. Acetylene Gas Explosiveness -

    Despite the "acetylene gas is not explosive true false" myth, acetylene is highly explosive between 2.5% and 100% concentration in air (NFPA 51B). Always treat cylinders as live sources and store them upright in a well-ventilated area. Recall the reaction formula C₂H₂ + 2.5 O₂ → 2 CO₂ + H₂O to appreciate the energy release.

  2. Flashback Arrestors & Check Valves -

    Flashback arrestors stop flame propagation into hoses and cylinders, adhering to ISO 5175 or CGA V-1 standards. A handy mnemonic is "ACE" (Arrestors, Check valves, Exhaust back”pressure protection). Regularly inspect and replace these safety devices every 6-12 months.

  3. Personal Protective Equipment (PPE) -

    Welding safety quizzes emphasize PPE: ANSI Z49.1 recommends flame”resistant jackets, auto”darkening helmets (shade 10 - 13), leather gloves, and steel”toed boots. Remember "Helmet, Gloves, Jacket, Boots" to cover all major hazards. Proper PPE prevents UV burns, sparks, and molten metal contact.

  4. Oxygen-Acetylene Welding Ratios -

    Maintain a neutral flame at a 1:1 to 1:2 O₂:C₂H₂ ratio to avoid carburizing (excess acetylene) or oxidizing (excess oxygen) flames. A neutral flame has a clear inner cone about 1/8" long and is ideal for most welds. Use the "Inner cone check" trick: if the cone swallows the base metal, reduce acetylene slightly.

  5. First Aid for Welding Burns -

    Apply the "S.T.O.P." method: Stop the heat source, Thoroughly cool with lukewarm water for 10 - 20 minutes, Over-the-counter pain relief, and Protect with a sterile, non-adhesive dressing (FDA guidelines). For third-degree burns or chemical burns, seek immediate medical attention. Keep burn creams and dressings in your on-site first aid kit.

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