Under normal circumstances and low pressures acetylene is a safe fuel, burns well and when added to oxygen will produce temperatures sufficient to melt metal. But acetylene is a very volatile gas at pressures above 15 psig. Shock or high temperature can cause this gas to ignite violently and the higher the pressure the less energy it takes to ignite it.. A properly functioning regulator on your burning rig is mandatory.
Reports state that a balloon two inches in diameter containing a 50/50 mix of acetylene and oxygen has the explosive force of one-quarter stick of dynamite. That can cause some serious injury and damage. If you inflated this same balloon to nine inches in diameter you increase the explosive force 80 times. EIGHTY TIMES. That's twenty sticks of dynamite.
How many of us have one hundred feet of burning hose wrapped around the handles of your torch cart ?? Now if you calculate the volume of one hundred feet of 1/4" hose it works out to about the same as a 9" balloon full of mixed gas. That means that if for some reason fuel gas enters the oxygen line or vice versa you have the potential for a explosion with the force of 20 sticks of dynamite. It's gonna ruin your day.
A backfire during brazing is a momentary retrogression of the flame back into the tip. It usually results in a momentary flame-out followed by reignition of the tip flame and is accompanied by a pop or bang, depending on the size of the tip.
In severe cases, however, hot products of combustion within the tip may be forced back into the torch and even the hose. Occasionally, such backfires ignite the inner liner of hoses (especially oxygen), resulting in the hoses burning through. Such backfires can cause injury.
A flashback is an occurrence initiated by a backfire where the flame continues to burn inside the equipment instead of being re-established at the tip. Flashbacks result in very rapid internal heating of the equipment and can destroy equipment quickly.
Usually a flashback is recognized by a whistling or squealing sound. The equipment will heat up rapidly and sparks may issue from the tip. The flashback should be extinguished by turning off the torch valves as quickly as possible. Different manufacturers may recommend shutting off either the fuel or oxygen first, but the most important concern is to get both valves closed quickly.
Generally, backfires and flashbacks occur from allowing a tip to become overheated, forcing the tip into the work, or providing insufficient gas flow for the size of the tip in use. If backfires or flashbacks occur frequently, the cause should be investigated.
To prevent these two problems, reverse flow check valves and flashback arrestors are available. These devices can prevent backflow of gases and flashbacks when operated and maintained in strict accordance with manufacturer's recommendations.
I can't stress enough the importance of having properly functioning equipment, it should be clean and in good repair. Of course the best safety situation would be to place the flashback arrestors with built in reverse flow check valves at both the regulators and the torch. This would protect torch, hoses, regulators and tanks. These devices are available at any welding supply house, large hardware outlet or auto parts dealer who carries gas equipment and supplies. Be sure to size them for adequate gas flow as units of insufficient size will lower gas flow and pressures.
I hope everyone takes this seriously. A small investment can save your precious projects, cars, buildings and more importantly... your life.
MISC SAFETY ITEMS FOR OXYGEN/ACETYLENE USAGE
Cylinders shall be used and stored in an upright position.
Be sure all connections are tight. Use soapy water to locate leaks.
Keep cylinders valves, regulators, couplings, hose and apparatus clean and free of oil and grease.
Keep cylinders away from open flames and sources of heat.
Safety devices and valves shall not be tampered with, nor repairs attempted.
Use flashback arrestors and reverse-flow check valves to prevent flashback when using oxy-fuel systems.
Regulators shall be removed when moving cylinders, when work is completed, and when cylinders are empty.
The cylinder valve should always be opened slowly. Always stand away from the face and back of the gauge when opening the cylinder valve.
When a special wrench is required to open a cylinder or manifold valve, the wrench shall be left in place on the valve stem when in use; this precaution is taken so the gas supply can be shut off quickly in case of an emergency; and that nothing shall be placed on top of a cylinder that may damage the safety device or interfere with the quick closing of the valve.
Fire extinguishing equipment should be readily available when combustible materials can be exposed to welding or cutting operations using compressed cylinder gases.
Things Not To Do:
Never roll a cylinder to move it.
Never carry a cylinder by the valve.
Never leave an open cylinder unattended.
Never leave a cylinder unsecured.
Never force improper attachments on to the wrong cylinder.
Never grease or oil the regulator, valve, or fittings of an oxygen cylinder.
Never refill a cylinder.
Never use a flame to locate gas leaks.
Never attempt to mix gases in a cylinder.
Never discard pressurized cylinders in the normal trash.
Below is an article that was distributed here at work. It shows what can happen without proper safety equipment and procedures. This is reprinted (with permission) from a Safety news letter issued by Alcoa, Inc at their Rockdale facility.
Oxygen-Acetylene Torch Set-up Catches Fire and Explodes!
Oxygen/Acetylene Torch Set-up Catches Fire and Explodes
Monday, 2001 June 18
An Ironworker crew was modifying a temporary structural steel bridge using an Oxygen/Acetylene torch set-up on a cart, a portable welder, and a grinder. Apparently the acetylene hose develop a leak and ignited during the grinding operation.
The torch set-up was not equipped with a "flashback" arrestor check valve and the fire traveled through the hose into the compressed cylinder.
A worker attempted to extinguish the blaze with a nearby fire extinguisher; however, he quickly determined that the fire was beyond his capabilities. The area was evacuated and the fire department was immediately dispatched to put out the fire.
Thankfully, there were NO injuries.
The Torch Set-up and nearby portable welder were damaged beyond repair. A structural engineer is reviewing the garage for possible structural damage.
Workers must inspect tools and equipment daily and immediately remove defective equipment from service.
All oxygen/acetylene set-ups must have a "Flashback" arrestor check valve at the regulators, NOT the torch head, to prevent this type of occurrence. This little device would have prevented this fire.
Literature on Victor "Flashback" Arrestors & Safety Check Valves is available via the attached link. Please take a look at all your torch set-ups on the project and make sure they have the required safety check valves to prevent this from reoccurring.
RCK-PUBLICTeamsSharedEHSDATASafetygramsTorch expl Victor check valves.pdf
For improved safety use reverse flow "flashback" arrestor check valves The use of check valves on regulators is strongly recommended to reduce the possibility of reverse flow of gas, which can create a dangerous mixture of fuel and oxygen.
Mixed gases will burn rapidly once the torch is lighted and can explode in the hoses, regulators, or cylinders, resulting in serious damage to the equipment and/or injury to the operator.
Reverse flow from one line to another can be caused by:
A damaged or plugged tip
Loss of pressure in one line
A cylinder emptying in use
Caution: Check valves should be tested for proper function at least every six months. Careless usage, dirt or abuse can shorten check valve service life and require more frequent testing.
Other resources for safety information and equipment:
other sources of information
The Welder's Bible by Don Geary