Once upon a time (a long, long time ago), The Doctor was called in to investigate an industrial accident that resulted in serious burn injuries to personnel in the heat-treat shop. As part of that investigation, the subject of what to do in the case of a quench-oil fire came up and became legend, when in a late night meeting the infamous phrase, “run baby, run” was uttered. Let’s learn more.
Our story begins with an innocent-looking batch integral-quench furnace, one that sent six people to the hospital suffering from severe burns. This particular furnace was manually operated, and its front (outer) door burn-off exited from a circular hole near the bottom of the door, about 50 mm (2 inches) in diameter. The burning endothermic gas exited horizontally. It was reported that flames suddenly erupted from the opening during production runs, and anyone caught standing in front of the furnace – as far as 4.5 meters (15 feet) away – was in danger of being burned.
Two supervisors, several heat treaters and a fellow from the nearby plating department were unlucky enough to be within range of the flames and were seriously burned. What caused the furnace to erupt the way it did, and what could be done to fix the problem, was the subject of intense debate. Enter The Doctor.
First, this puts renewed emphasis on the fact that no one should stand in front of a furnace door for longer than is absolutely necessary. You would be amazed by how many conversations are held by people standing in close proximity to a furnace door. Don’t do it!
Secondly, a temporary solution to the problem was to change the direction of the burn-off by adding a 90-degree elbow into the outer door, thus changing the flame direction from horizontal to vertically upward. A small hole in the bottom of the elbow allowed the pilot flame to ignite the endothermic gas. This is one of the reasons that many furnace atmosphere burn-off cans are moved up and away from personnel (Fig. 1).
The investigation then began in earnest. A careful check of the furnace and transfer sequence found nothing out of the ordinary. In fact, the flame eruption was occurring mid-cycle and not during load transfer. One rather strange clue was found on the factory floor, an “X” marked in chalk that coincided with the distance the flames traveled horizontally outward from the outer door when the inner door was opened (such as when a load was being transferred to or from the quench vestibule). A second clue was a small remnant of twine wrapped around the manual-activation handle for the inner-door cylinder. Could this be a case of deliberate intent to harm?
It turned out that a disgruntled furnace operator had indeed discovered how to make the furnace belch flames and how far the flame would extend out in front of the furnace. Positioned out of sight behind the furnace when someone he didn’t like “came within range,” he tugged on the string attached to the inner-door open activation handle, causing the inner door to open with an eruption of flames out the front door. This is only one of two instances of criminal acts The Doctor has ever witnessed in the heat-treat shop. Amazing but true.
As part of the investigation, managers from several operating divisions had gathered to learn from the event. One of the other subjects of intense interest was what to do in the event of a quench-oil fire. What started as a lively discussion over lunch extended far into the evening talking about the do’s and don’ts related to quench-oil fires. Since one of the most dangerous conditions is a load jammed half in and half out of the oil, this was the principal focus of everyone’s attention. Oil discharge from the overflow pipe into the pit was also mentioned, however. At this time The Doctor related a true story about a similar situation, where up to 100 mm (4 inches) of oil had accumulated in the pit and was ignited by a careless employee, destroying seven integral-quench furnaces and a large portion of a heat-treat department.
A brief recap of the discussions follows.
- The subject of equipping furnaces with a nitrogen purge (Fig. 2) was raised almost immediately. Everyone agreed it was a good idea, but the reality was that most of the company’s integral-quench furnaces were not equipped with this feature. A management action item was undertaken. One interesting part of the discussion centered on a sintering furnace in which the empty nitrogen-purge cylinders had been replaced by oxygen cylinders (despite the fact that they had left-handed threads). One of the engineers stated that it is still the single loudest explosion he has ever heard … and he was in an adjacent building.
- Also discussed was educating supervisors not to give instructions to “shut everything off” (which included the nitrogen-purge cylinders) in the hopes that the fire will burn itself out. An entire plant was lost because of this mistake.
- The question was raised if the front door should ever be opened “just to take a peek” while flames are erupting and the hot load is still volatilizing the quench oil. Surprisingly, this sparked a heated debate as to whether this technique should or shouldn’t be used. Several managers stated that they gather a crew of trained individuals in proper personal protective equipment; open the door; and, using long rods, attempt to clear the jam in an effort to move the load either down or up out of the oil. Others, including The Doctor, view this as putting personnel in unnecessary danger.
- Who should be your first call? Is it to your supervisor, his boss or 911? While most fire departments do not train for heat-treat-related emergencies, they are trained professionals that deal with fire events all the time. Since, for example, a grease fire in a kitchen can get out of control in as little a 30 seconds, remember to act quickly and responsibly. Confirm by asking that someone has indeed called the fire department.
- Should the furnace ever be placed in manual mode and the operator attempt to reposition the load? The consensus was that this is a prudent act to perform provided one can do it safely and it does not involve attempting to open the front door.
- Where is the control panel in relationship to the front door? In many instances it is next to it, perhaps convenient during normal operation but unsafe to stand in front of in emergency situations. While relocation of the control panel may not be an easy task, everyone was in agreement it should be on the side of the furnace, away from the door area. Remember that the pressure inside the furnace builds up, and one of the ways it will relieve itself is to push the front door outward away from its mating flange. The Doctor has seen 1-meter (3-foot) flames driven out horizontally under high pressure at the front door during such situations, so beware!
- How often should grids and baskets be inspected, and do you attempt to weld repair a grid in order to extend its life? Grids and baskets should be inspected daily for cracks, warpage or other signs of damage. If your application is carburizing, weld repairs will fail quickly. Grids that tear apart are a major cause of load jams.
- What other scenarios can cause fires? There are obvious dangers that most of us are taught to watch out for, such as water in quench oil that can cause a quench tank to erupt into flames. Another subtle but important consideration is the makeup of our workloads. We must pay attention to surface area and remember that whether we are running tiny fasteners in an integral-quench furnace or moving large, heavy parts by crane for quenching into an open tank, the transfer must be smooth, performed in a timely manner and the load must be fully submerged. Huge evolutions of flame may be dramatic, but they are deadly!
While we all had a good laugh over the fellow who uttered “run baby, run” when faced with immediate danger, his comment hits the mark in many ways. When faced with an emergency, it is only human nature to protect one’s life first. This is where knowledge, understanding and training of operators, supervisors and managers helps everyone make informed decisions.
When is the last time your shop had an emergency drill to practice various dangerous scenarios that can arise? Never assume that the person next to you has clearly heard or understands your commands. Asking them to repeat your instructions is always a good idea. The Doctor still remembers shouting “don’t spark the pilot” then holding on to a ladder about 20 feet in the air (in a horizontal position to the floor) because the salesperson, trying to be helpful, thought he heard “spark the pilot.”
The bottom line is accidents happen, but we don’t want people injured because of them. Train, train and train some more.