Characteristics of Burning Bars Important to Their Being Used for Underwater Salvage Operations
Authors: Alexander G.H. 
Published: October 2008

On first consideration, the burning bar might seem to be a valuable tool for underwater salvage operations. It can melt almost any material from iron to concrete, and it is relatively inexpensive to make. However, it does have a number of serious drawbacks, the most dramatic of which relates to safety.

Because of reports of burning bar use in underwater work, and because of other reports concerning potentially hazardous overpressures, the Supervisor of Salvage, Dept. of the Navy, authorized a Battelle study of the potential of burning bars for salvage operations. The results of that study, which are presented here, indicate that, because of the random explosion of large gas bubbles formed during operation underwater, burning bars cannot be considered safe to use. Although. extensive research and development might make it possible to predict and control these explosions, reduce their intensity, or even eliminate them, the expense involved and the fact that comparatively safe equipment with similar capabilities is available, make the present value of any efforts to improve the burning bar questionable. However, burning bars are the only method presently known for cutting concrete by melting.

BURNING BAR DESIGN AND OPERATION

A burning bar, as shown in Fig. 1, is a long ferrous metal tube filled with ferrous or nonferrous wire or rods. The rods are normally held in place by crimping the tube. When pure oxygen is forced through the packed tube and the exhaust end of the tube has been heated red hot, the oxygen combines with the iron and forms iron oxide, giving off large amounts of heat in the process. This heat maintains the end of the tube at a sufficiently high temperature so that a continuous burning process may occur. To burn or cut an object, the very hot tube tip is pressed against it. If the material is readily oxidizable, such as iron, aluminum, magnesium, etc., the metal melts due to the heat given off by the reacting iron and combines with excess oxygen coming through the tube. The resultant reaction quickly cuts a hole. If the material does not oxidize readily [e.g., concrete, brick or brass], the material is melted and flows or is blown away.

INVESTIGATION OF REPORTED OVERPRESSURES

At the beginning of the investigation of the overpressure level associated with underwater use of the burning bar, various remotely controlled experiments were conducted. However, results were not conclusive. Data indicated overpressures close to, but not in a hazardous range. To obtain further information tests were then conducted with divers using the bar to cut metal under water. Results indicated that the continuous overpressure was not hazardous, but that the random explosions that can occur could be quite damaging.

Source of Random Explosions

In an effort to determine the source of the random explosions, the gases given off during cutting were trapped and analyzed. The results indicated a very high concentration of hydrogen, -with the remainder of the gas being primarily oxygen. The concentrations of hydrogen in oxygen found were well within the flammability and detonation limits of the gases.