Safety
I/EC
Terf-Butyl Peracetate — An Explosive Compound
by Joseph J. Martin, University of Michigan
Editor's Note Dr. Martin proposes a theory to explain the ex plosion and reports experi ments which prove that r a p i d heating to a critical tem perature will cause pure ferrbutyl peracetate to explode. W h a t actually caused the explosion, if Dr. Martin's theory is correct, and what started the fire which caused the r a p i d heating have never been discovered.
The 1 9 5 3 remnants of building C of the Lucidol Plant. This is where the condensation reaction was conducted. Note that h a r d l y a thing was left standing in this building so complete was destruction
reaction was installed in a ventilated metal hood. At the bottom of the hood was an access door where an operator would place carboys to be filled with liquid lert-buty\ perace tate product after it was separated from its aqueous phase. According to the usual time schedule of opera tions, it appeared that a fresh batch of /«-/-butyl peracetate had just been prepared and was about to be drawn off into the carboys when the first of several explosions occurred, described by witnesses as being somewhat milder than the later ones. Explosive Sequence
^ • N September 23, 1953, an ex plosion occurred in the Novadel Agene Corporation's Lucidol Divi sion plant at Tonawanda, Ν. Υ. Eleven persons lost their lives and a number of others were injured. In the course of the subsequent investi gation a considerable amount of testimony was obtained from wit nesses working near the scene of the accident or who were familiar with the company's operations in that area. On the basis of their evidence it was possible to reconstruct the most probable setting and circum stances under which the explosion occurred. Process I n v o l v e d
In the building which was de molished by the explosion and ac companying fire, one of the chemical processes which was being conducted involved the condensation of tertbutyl hydroperoxide and acetic an hydride. Equipment used in this
7>r/-butyl peracetate forms in flammable mixtures with air, so it is presumed that the first mild ex plosion may well have been the com bustion of just such a mixture. Possibly some vapor may have es caped from the hood when a work man opened the door to fill a carboy. The vapor, being heavier than air, may have crept along the floor and been ignited by an electrical spark, a torch, falling objects, or the like. It is equally possible the mixture of air and vapor was ignited within the hood itself by a spark from slamming the door or an electrical spark, though precautions had been taken against such an occurrence. The first explosion probably caused only a small amount of damage such as blowing out the walls of the hood. However, the burning of the vapor and air could easily have heated up the fresh batch of to7-butyl perace tate to temperatures above 250° C. At this condition it is now assumed that explosive decomposition took place. This was much more violent
than the initial explosion and caused fire to break out all over the building as other inflammable materials were ignited. During the course of the fire several of these violent explo sions occurred. Damage
Examination of the wreckage re vealed that several holes had been blown in the concrete floor which was laid directly on the ground. One of these holes was at the position where blueprints showed the terlbutyl peracetate reaction unit to have been located. The other holes were at locations where carboys of ter/-butyl peracetate were known to have been stored preparatory to shipment from the building. Al though ignition of confined mix tures of an inflammable vapor and air can produce explosions, it is highly unlikely that such explosions could do much damage to a con crete floor. Therefore, the only reasonable explanation of the holes in the floor seemed to be that the to-/-butyl peracetate must have det onated in a violent decomposition chain reaction. This seemed par ticularly likely because of the known explosive characteristics of other peroxygenated compounds. How ever, amidst all of the evidence pointing in the direction of this theory, there stood out one some what conflicting piece of informa tion. This was a report from the Bureau of Explosives of the Depart ment of Commerce. Bureau's Report
A number of tests had been per formed on a sample of fer/-butyl perVOL. 52, NO. 4
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APRIL I 9 6 0
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SAFETY acetate received from Lucidol. Appropriate quotations from that report are as follows: A portion of the liquid was placed in a loosely stoppered glass vessel and maintained at 75° C. for 48 hours. The material evaporated almost completely during the incubation—there was no sudden decomposition. The liquid burns very rapidly when ignited (in small quantity). The combustion is somewhat peculiar in that the liquid burns rapidly when first ignited, subsides somewhat, and then the combustion becomes rapid again. The liquid does not flash below 80° F. when tested in the open cup apparatus. Small portions of the liquid were placed in loosely stoppered glass tubes and these partially immersed in an oil bath and the temperature gradually increased. Fumes were evident at 110° C. but when the temperature of the bath had reached 140° C , the liquid was completely evaporated without any sudden decomposition. A portion of the liquid (unconfined) was subjected to detonation of a blasting cap. There was considerable white fume evolved—the decomposition was sudden but not a violent explosion. This test was repeated using sterile absorbent cotton and dry wood flour (in turn) saturated with the chemical. On detonation of the blasting cap there resulted a rather violent explosion with both mixtures. Small portions of wood flour saturated with the sample liquid were subjected to impact test in the impact apparatus. No explosions resulted under drops of 10 inches. A mixture of wood flour saturated with the sample liquid was placed in a fiber tube and this placed in the center of a hot wood fire. The mixture burned rapidly but without explosion. A portion of the sample liquid was placed in a tightly stoppered glass bottle and this placed in the center of a wood fire. The bottle ruptured and the liquid burned without explosion. From these tests it did not appear that tert-butyl peracetate would decompose explosively from a mere application of heat. In fact, in only one of these tests was any explosion obtained, and that required the detonation of a blasting cap. Also it was not the pure liquid which could be exploded with the blasting cap, but a mixture of the liquid 66 A
and a combustible organic compound such as would be in cotton or wood flour. This seemed more indicative of a sudden oxidation reaction rather than a decomposition of the peracetate compound. On the basis of these tests it was difficult to see how tert-butyl peracetate could explode when contained as a liquid in a carboy or process tank. However, conditions in the plant might have been much more severe than those in the laboratory tests, particularly in regard to the rate of heat transfer. In the plant it was possible that the radiation from a hot fire or intense combustion flame of a vapor-air mixture might supply heat to a batch of liquid at a very high rate. If the container did not break, the liquid might even be superheated before it would evaporate. Therefore, a decision was made to try another type of explosion test. Explosability Tests
A sample of 7 5 % /«-/-butyl peracetate in benzene was obtained from Lucidol. As the material which had been produced and stored in the plant at the time of the explosion was not in solution, it was necessary to separate the peracetate from the benzene to perform a representative test. The literature showed that the vapor pressure of benzene is higher than that of all other compounds having the same percentages of carbon, hydrogen, and oxygen as tert-butyl peracetate. It was surmised, therefore, that in a distillation benzene should be distilled off leaving the peracetate as the residue, provided there was no formation of an azeotrope. Hightemperature distillation was obviously ruled out because of the very nature of the theory of the explosion. Consequently, a low-temperature vacuum distillation was conducted with the distillate being collected in an ice trap. Approximately 10 ml. of the 7 5 % solution were distilled until the volume in the still was reduced to about 7 to 8 ml. This residue was assumed to be a more pure form of /«r/-butyl peracetate and was taken for the following explosability test. To accomplish rapid heating of a sample of liquid, heat was supplied from the inside instead of from the outside. In this technique superheated vapor could be produced
INDUSTRIAL AND ENGINEERING CHEMISTRY
without evaporating the liquid. The scheme of heating was very simple : Approximately 3 inches of 36-gagc chromel wire was formed into a small coil. The coil was soldered to two copper lead wires which were connected to a 7- to 13-volt transformer. The coil was shown to get red hot in air when the voltage was turned up. However, it could be darkened immediately by blowing on it or by inserting it into water which would start to boil after a few minutes. The power consumption of the coil was estimated to be about 50 watts at full voltage. The coil was inserted into a small play-type bottle of about 40-ml. capacity. The bottle was placed behind a concrete block wall with a mirror so positioned that the bottle could be seen from a safe distance. The lead wires were run to the transformer some 15 feet away. The tests were run at night so that flames might be observed. A light was turned on and off periodically for further observation. The 7 to 8 ml. of residue from the distillation were poured into the bottle when it was cold. This completely covered the heating coil. The top of the bottle was wide open except for the small lead wires. After the transformer was turned on, nothing happened for about 30 seconds. Then white fumes were detected coming from the bottle. Approximately 20 seconds later there occurred a violent explosion which sounded about like the report of a high-power 30-calibre rifle. There was no apparent flash, however. The bottle had been standing in some gravel. No trace of the bottle could be found and the gravel was blown away for a radius of about 4 inches. The lead wires were burned, broken, and dented inward in a peculiar way. There was now no question about the explosability of /
