BY RONALD MORITZ
At a recent incident, a support column exploded after being exposed (partial exposure) to open flame for a few minutes. The column was 10 feet long with an outside diameter of 4.5 inches. The material was 7/32 inch thick. The column was used to hold up a steel girder within a wood structure. The building was approximately 25 years old and in a deteriorated state. It had been abandoned and unheated for several years and was purposely being razed for redevelopment of the land. When exposed to enough heat for a period of time, the column exploded as the result of internal pressure. It did not fail because of the weight it was carrying. If that had been the case, when it got hot enough to weaken the steel, it simply would have softened, bent, and become distorted.
This column was set in a corner of the building where two wood-frame walls met and made a right angle. When failure occurred, the resulting explosion heavily damaged and knocked down both walls. The newly created two halves of the column landed approximately 20 feet apart outside the building; both mounting plates were torn free in the rupture.
Not all support columns similar to this one will fail. At this incident, only one out of 11 failed even though all encountered similar fire conditions. Failure of the column will depend on five factors:
- The original construction method.
- The quality of the original construction.
- The existence of any holes in the column.
- The collection and presence of moisture within the column.
- Time of exposure to fire and temperatures reached during the exposure.
ANALYSIS OF FAILURE FACTORS
Let’s apply the above factors to this specific column and similar columns.
This column was originally made from three separate pieces of steel. One piece was a cylinder with a flat piece of steel welded to each end to enclose the column and also act as mounting plates.
This column was originally a flat piece of material that was rolled into a straight cylinder shape during manufacturing. If you look at the edges of the column in the photos, you can see that one is smooth while the other is jagged. This column ruptured and split the column at approximately half of the length of the column. This leaves each piece with the seam separated as well as a jagged edge where the steel tore apart.
(1, 2) Two views of the overall destruction of the column. (Photos by author.)
The smooth edges were touching each other when being formed and were bonded by heating when manufactured, but they were never truly welded prior to being destroyed. Welding would have caused the steel to be molten and intermixed and would have eliminated the possibility of the forming of a clean edge when it failed. This bonding process is strong, obviously enough to allow great amounts of pressure to build up without leaking.
The jagged edges of the pieces obviously are a result of the material’s being torn when the column failed. In matching the two halves of the damaged column, it was noted that several pieces of the column were missing. They became shrapnel! Some pieces were microscopic in size; others were several inches in length and width.
(3, 4) One edge of steel was jagged and had turned some of the steel edge into shrapnel. Photo 4 shows a closer view of the edge.
What creates the danger and potential for an explosion is if the column is hollow and a complete seal is formed when the end plates are welded onto the ends of the cylinder. In a hollow column, if the end plates were poorly or only partially welded, they would not be sealed completely. In those cases, vapor could escape and the column would not explode, for it could release the internal pressure that increases with exposure to heat. At the same time, a column that was sealed at the ends when welded would also have a pressure relief if a hole were ever drilled into the column.
This column had been exposed to a Class A fire for less than 10 minutes when it failed. A large portion of that time was simply radiant energy. A few minutes prior to failure, approximately the top quarter of the column was engulfed in flames.
(5) The piece of steel at the top of the photo shows the smooth surface of the bottom edge. The steel was flat before it was rolled into a cylinder so that the two outside edges touched and were bonded together.
These columns can be found in buildings when open spans require supports for beams or girders. They can be found in commercial structures, stores, industrial occupancies, agricultural buildings, residential buildings, basements, anywhere. They may be covered with an interior finish such as wood, plastic, or fiberglass products to make them more decorative.
I have actually recognized this “column explosion” once before. (Looking back, I may have inadvertently seen it or the end results other times but did not recognize what had taken place.) The other time I witnessed a column explode was at a very similar fire situation. The fire involved a wood structure on a farm. This explosion occurred just as fire companies were arriving on the scene. In that fire, basically the same condition was present-a hollow cylinder-shaped column with short-term fire exposure. In that case, one piece of shrapnel was found about 200 feet away from where the column was originally mounted. That piece of shrapnel, traveling at about 4 1/2 feet off the ground, put a three-inch-diameter hole through a wood garage door of another building.
Recently, I responded to a smell of something burning in a townhouse. Nothing was obvious on arrival, so during the investigation I inspected the basement for a source of the smell. I did not find the cause until later (next door neighbor’s dinner rolls), but in the basement I did find a welded steel column standing upright alongside the staircase holding up a wood crossbeam that supported the main floor. Was it sealed? Was it hollow? Would it fail as firefighters crawled down the stairs alongside it to fight a basement fire? I don’t know, but I do know enough to Respect the Column!
RONALD MORITZ, a 30-year veteran of the fire service, is a career captain with the Skokie (IL) Fire Department and a paid on-call lieutenant with the Woodstock (IL) Fire Rescue District. He is a certified Illinois fire officer III and has a master’s degree in human resource development from Webster University in St. Louis, Missouri.