In the March/April 2002 issue of the Iron-Men Album I wrote two articles on fusible plugs examining both the history of fusible plugs and the condition of fusible plugs in my own equipment. The first article was an attempt to garner an historical perspective of the importance placed on fusible plugs, while the second article focused on the capacity of the fusible plugs in my own equipment to perform as intended. Both articles were motivated by my need to understand conflicting statements I read about the tragic explosion of the Case 110 on July 29, 2001 at the Medina County Fairgrounds.
In this article I have used results from the investigations I documented in the two previous articles to raise some questions related to understanding the disaster in Medina. To this end, I have focused primarily on three findings from the Medina County Sheriff's report. I have tried to confine comments to verifiable facts, and I have also tried to note those places where I am aware of having digressed into speculation.
The Medina County Sheriff's report states that the water level in the boiler of the Case 110 was low. In its summary of the causes of the explosion and the failure of the Case's crown sheet, the report states on page 18, Section 1, that, "This failure most likely occurred due to a lack of sufficient water in this area to insulate the already structurally weakened stay bolts and sheet and over firing." The report goes on to say that, "Apparent over firing and failure to maintain an adequate, constant water level" was a critical factor in the explosion.
As for the fusible plug, the Medina County Sheriff's report clearly states the fusible plug did not melt. In Section 2 of the report, an Aug. 10, 2001 letter from Dean Jagger, chief boiler inspector for the state of Ohio, to Lt. John Detchon of the Medina County Sheriff's Office states simply: "Fusible plug was still intact; the center had not melted out."
Additionally, John F. Wallace of the department of Materials Science and Engineering at Case Western Reserve University led an investigation team that examined the fusible plug from the Case 110. An Aug. 3, 2001 letter from Wallace to Lt. Detchon states: "The examination of the contents of the fusible center of the tractor plug and the melting temperature of the central contents of the small plug section showed that it was produced from 100 percent tin. The center section of the new plug obtained by Bill Kennedy was also 100 percent tin. Both of these materials have a melting temperature of just under 450 degrees F, or 232 degrees C; The fact that the material was the same and did not melt indicates that these plugs were not the direct cause of the failure." The Sheriff's report concludes that the metallurgical laboratory found the soft plug to be good.
Understanding the Facts
One of my difficulties is that I cannot understand how all three of these statements can be true.
There seems to be general agreement that the water was low. However, there also seems to be some question as to how low it was. I am assuming that the water was low enough to expose the fusible plug. I am basing this on the assumption that if the water was high enough to cover the plug when the front of the engine was slightly raised, the water level must have been lower when the engine was level as it entered the fairgrounds. At that time some of the water that was near the soft plug when the front was raised would have filled a greater portion of the barrel of the boiler, and the water level would have then been below the soft plug.
I have not seen the path of the engine into the fairgrounds, but John Provencher, who is familiar with the fairgrounds, tells me that, "There is a slight uphill grade and then a pretty substantial downhill grade, which surely would have caused the water to slosh to the front of the boiler exposing the rear of the crown sheet if the water was that low." It is difficult for me to imagine how, under these conditions, a good fusible plug would not have melted. This is one place where I have allowed myself to speculate about conditions.
I have heard considerable discussion concerning whether or not the crown sheet of the Medina boiler sloped to the rear, along with speculation that a sloping crown sheet caused the plug to be covered with water, thus preventing it from melting.
Working from portions of J.I. Case drawings that Lt. Detchon gave me, the photographs in his report and the J.I. Case drawing in his report I have constructed a drawing of a 32/110 HP "pre-Canadian" J.I. Case boiler (see the image gallery to view the drawing) that I believe to be very similar to the Medina boiler (The boilers made by J.I. Case after 1910 complied with the strict Canadian standards. It is believed that the Medina boiler was made in 1908).
I recognize that there are some differences. For example, the dome on the Medina boiler is semi-spherical, whereas the one in the drawing from which I worked is flat. I believe I am correct in showing the boiler with the short smoke box, which was typical of the earlier Case engines. I regret I did not have the opportunity to work directly from the Medina boiler in making the drawing. Everything I have seen indicates that my drawing is an accurate representation of the crown sheet, and it does not slope to the rear.
There also seems to be no question as to whether or not the fusible plug melted. I have seen the photos and I have held the piece of the crown sheet that contains the fusible plug. The plug that I saw had not melted. If the above conditions are accepted as true, then the only factor that can remain in question is whether or not the fusible plug was defective.
Lt. Detchon informed me that metallurgist Ron Brockway was involved in the analysis of the fusible plug. I contacted Brockway, and he told me that no attempt was made to melt the fusible plug to determine its melting point. Instead, it was "shot" with a spectrograph to determine its chemical composition, and using the composition recorded on the spectrograph its melting point was determined from data in a handbook. It was a similar procedure that indicated that the two fusible plugs I had tested for my article in the March/April issue of IMA would melt at 360 to 460 degrees F. As I outlined then, those plugs could not be melted at temperatures as high as 1,000 degrees F.
The Sheriff's report also states that the fusible plug in the Medina Case may have been installed by brazing and that this had been confirmed. In Section 7 of the report, photo number 34 of the fusible plug shows a golden-colored (brass?) halo around the fire-side of the fusible plug.
The fusible plug from the Medina engine is clearly visible in the center of this picture from the final report. The Medina County Sheriff's final report notes that the bushing for the plug had been welded into the crown sheet.
In Section 2 the report states, "The center area of the crown sheet had been cut away to allow metallurgical examination of the metal and evaluation of the fusible plug. The fusible plug did not melt and it was reported that it might have been installed with the use of brazing. A subsequent report from Lt. John Detchon confirmed this and that the plug metal was tin. The area of the crown sheet which was removed was reported to have a red colour tone, which is indicative of overheating."
If the above statements are true, I cannot understand how a good fusible plug could have been brazed into the bushing in the crown sheet without melting the tin out of the plug. The lowest melting point for a brazing alloy that I could find in an industrial supply catalog was 1,125 degrees F. Also, if the red color of the crown sheet is "indicative of overheating," it seems that it would also support the need to question the viability of the fusible plug.
In Section 1 the report states that, "The bushing for the plug on this tractor was welded into the crown sheet, apparently due to a prior leaking condition and appeared that the hexagon part of the plug was chiseled and or twisted off in an attempt to remove it." The authors of the report do not state the source of the information indicating that this occurred in an attempt to remove the plug. Another scenario might be that the head was twisted off in an attempt to tighten the plug to stop it from leaking.
It's also unclear how they determined that the head on the fusible plug was hexagonal and not square. A square head would have possibly indicated a much older plug than would a hexagonal one. Both of my plugs that failed to melt at 1,000 degree F had square heads. When tightening the plug would not stop a leak, is it possible that whoever was doing the work then resorted to brazing? I am merely speculating on this point.
In December of 2001, I visited with Lt. Detchon in his office at the Medina County Sheriff's Department. He graciously spent a considerable amount of his day filling me in on the volumes of information he had collected in his investigation. Much of our time was spent in the evidence room, where many of the small, critical components of the engine are stored.
One item I was able to view was the fusible plug from the Medina Case, and I was surprised to see how cleanly the tin in the plug appeared to have fractured, apparently when the head was twisted off. However, it is possible that what I saw was not a fracture, but rather the exposed end of the tin that may have never extended into the portion of the plug that was removed. This was not my impression at the time, but I believe it is important to acknowledge the possibility.
Pure, unoxidized tin is a very malleable metal that does not fracture without considerable deformation. However, the surface of the tin on the fireside of the Medina plug did not show the signs of oxidation that I observed on the plugs I tested and on other used plugs I have seen. It's possible this is due to the tin's having fractured, or it could be because the fusible plug was fairly new and had not yet oxidized on the surface, as do all fusible plugs after some use. Again, on this point I am speculating.
After leaving the Sheriff's office, I realized that the work I had done on fusible plugs was a double edged sword. The good side appeared when Lt. Detchon, recognizing the value of what I had studied, kindly made his sources of information available to me. The down side appeared when he informed me I could expect to be subpoenaed.
Back in November, after receiving the metallurgical results on the fusible plug from my Case engine, I wrote letters to John Payton, chief boiler inspector of Pennsylvania, Dean Jagger, chief boiler inspector of Ohio, and the National Board of Boiler and Pressure Vessel Inspectors. In these letters I urged the recipients to do whatever possible to get a determination, one not based on data from a handbook, of the melting point of the fusible plug from the Medina engine. The only response I received was from Mr. Payton, but he did not address my interest in having the Medina plug tested.
I am fully aware that should the fusible plug from the Medina engine ever be tested – as I had my plugs tested – it may be determined that its melting point is indeed 450 degrees F, as reported. However, if the melting point should prove to be much higher, I believe that information could dramatically change some of the conclusions that can be (and have been) drawn regarding the cause of the Medina explosion. Even so, I truly believe the information I have obtained should be adequate to compel someone to insist that the melting point of the plug be determined so we can learn more about the causes of this disaster before we react in a manner that may later prove to be inappropriate.
One final thought: I have never read, nor heard anyone say, that we need to be concerned with low water and defective fusible plugs only in old and deteriorated boilers. What would have been the outcome if there had been a new boiler on the Medina engine?
I want to acknowledge the valued contributions of technical information, editorial assistance, probing questions and encouragement from Dr. Robert T. Rhode. Charles Provencher and John Provencher both provided valuable information and suggestions. I also want to acknowledge Lt. John Detchon's contributions of both his time and the copies of the investigation documents he provided that were so important to putting this article together.
Steam enthusiast Bruce E. Babcock is a regular contributor to the Iron-Men Album. Contact him at: 11155 Stout Rd., Amanda, OH 43102, (740) 969-2096.