The Portable Oxy-Fuel System Debate
Unintentional leaks of gases from an oxy-fuel unit can be largely prevented by correctly operating and caring for the unit.
- By Kris Bancroft
- Mar 01, 2005
FOR some years now, there has been a debate over whether it is safer to leave a portable oxy-fuel welding and cutting unit in a constant state of readiness for use, or whether the unit should be disassembled when it will not be used for "X" period of time. Both schools of thought present some valid arguments. This article will discuss the pros and cons of each view and present the opinion of the author.
Two assumptions are made in answering this question:
1. The portable oxy-fuel unit is comprised of a sturdy cart that is designed to transport one oxygen and one fuel gas cylinder; the cylinders are substantially secured to the cart; the cylinders are fitted with regulators designed for their specific purposes; hoses are in optimal condition; back flow preventers, flashback arresters, and torches are in optimal condition; the employee using this unit has been properly trained; and the employee is competent to perform the assigned task.
2. The fuel gas consumption rate for the portable oxy-fuel unit is equal to, or greater than, one #3 cylinder of fuel gas per calendar quarter or the portable oxy-fuel unit is part of an emergency response plan.
Although there are no specific regulations stating that a dust cover for the unit should be provided, it is definitely a smart move to keep the unit protected from dust, dirt, and moisture when it is not in use.
The central theme of those who argue against leaving a portable oxy-fuel unit in a constant state of readiness is to play the scenario where the unit is knocked over and one of the valve heads is broken loose. Certainly, the potential result of unleashing an unguided missile propelled by as much as 2,200 PSI of oxygen is the stuff nightmares are made of. However, it is perhaps the realization of this potential disaster that has prevented such incidents. A diligent search for injury data in which events occurred similar to that described here has yielded no results in what might be called "recent history."
Even so, the above scenario can be easily prevented by the application of some administrative and engineering controls. To defeat such a disaster, the employer should (and mostly does) designate an out-of-the-way place where the portable unit shall be stored when it is not in use, provide a fixture that would allow the unit to be restrained in its upright position should something or someone unintentionally exert force against it, and train the worker to store the unit in this specified location when it is not in use. The "fixture" could be something as simple as a short piece of rope tied around the portable oxy-fuel unit and a structural member. Restraining cylinders in this fashion is consistent with the regulations provided in 29 CFR 1910.253 (b).
Another nightmare pertaining to portable oxy-fuel units is the unintentional release of fuel gas. Acetylene, the most common fuel gas, has one of the widest mixture ranges between its lower and upper explosive limits (LEL and UEL) of all gases.
The combination of an unintentional release of acetylene into the atmosphere of a workplace combined with an errant spark when the ratio of fuel gas to oxygen falls between the LEL and UEL would certainly qualify as a formula for disaster. However, the same mixture of acetylene and ambient air could be produced when a fuel gas cylinder in storage leaks or is not properly closed. In either case, the most common cause of an event related to explosions from leaking welding fuel gas would be the same: human error. Almost all human error in the workplace can be rightly assigned to inadequate training. (See 29 CFR 1910.253 (b).)
Better Care and Handling
Based on some years of observation, the greatest lapse in training of employees who are assigned to perform welding and cutting tasks is probably in the care and handling of the equipment they use. Therefore, it seems that unintentional leaks of gases from an oxy-fuel unit can be largely prevented by correctly operating and caring for the unit. One thing that will help a great deal is to use a consistent and sensible method of shutting down an oxy-fuel unit. The generally accepted best method is as follows:
1. Turn off the oxygen at the torch.
2. Turn off the fuel gas at the torch.
3. Turn off the oxygen at the cylinder.
4. Turn off the fuel gas at the cylinder.
5. Bleed the oxygen off the system (from the valve to the burner tip) by opening the torch valve. Observe the pressure drop on the oxygen regulator. Close the oxygen valve on the torch.
6. Bleed the fuel gas off the system by opening the torch valve. Observe the pressure drop on the fuel gas regulator. Close the fuel gas valve on the torch.
7. Observe both regulator gages; if pressure is registered on the regulator gages, there is a leak in the corresponding cylinder valve.
8. Release the diaphragm pressure on the oxygen regulator until the screw turns freely.
9. Release the diaphragm pressure on the fuel gas regulator until the screw turns freely.
10. While taking care to not place a strain on the hoses and fittings, coil the hose in its proper place on the cart and place the torch in its receptacle. In other words, leave the unit in the condition in which you would like to find it.
Just as the occurrence of events in which portable oxy-fuel units have been tipped over and the valves knocked loose from the cylinders seems extremely rare, the history of events in which components of these units have failed because of faulty assembly techniques is prolific. Keep in mind, as well, that most of these events are never reported to the employer, much less do they escalate into a reportable incident.
It is fair to assume that each time a thing is disassembled and reassembled by human beings, the probability the next reassembly will be performed incorrectly grows exponentially. The things that can go wrong when portable oxy-fuel unit components are assembled include: foreign matter entering the system; regulators, hoses, or torch fittings may be cross-threaded; or the connections will be improperly torqued.
When welders are asked why they failed to assemble the unit properly, the most common responses seem to be:
1. "I was being rushed into getting the job done quickly, so I didn't have time to do what I felt was right."
2. "The working conditions (darkness, cold, rain, snow) were horrible, and I was having enough difficulty in contending with the . . . ."
3. "I was being rushed so much that I didn't have time to find the proper tools to make good connections."
Regardless of whether it is implied or overtly stated, every task ever assigned by any employer carries with it the message of some degree of urgency expressed to the employee; this is especially true when a production line is shut down or when there is a bona fide, life-threatening emergency. To that end, it seems obvious that safety is best served by keeping the portable oxy-fuel units continually ready for immediate use.
Note: If the unit is to be transported, one should disconnect the regulators from the cylinders, install any protective caps over the valves--if the cylinders are so designed--and secure the cylinders (in an upright arrangement) in a manner in which they will be substantially protected during transport.
This article appeared in the March 2005 issue of Occupational Health & Safety.
This article originally appeared in the March 2005 issue of Occupational Health & Safety.