The two-story brick building at 1 Allen Street was built in two sections. The first section was built as an armory in 1858. A second section added in 1901 which paralleled Allen Street was the location of the incident. This "newer" section was constructed of brick and cast iron. Its floors were brick arches supported on cast iron beams, with a concrete cover on top overlayed with heavy wood plank. In the interior of the building, the floors were supported by cast iron columns. The slate roof was placed on wood purlins supported by cast iron truss work.
The occupant of the area in which the incident occurred was Advanced Laboratories, Inc., manufacturers of tablets for chlorination of swimming pools. They occupied the first and second floors of the newer section of the building.
The "chlorine" tablets were produced by mixing raw materials including trichloro-S-triazinctrione known as TCT (trichloroisocyanuric acid) in a mechanical blender and pressing the resulting mixture into tablets. When TCT is exposed to water, heat is released. In the presence of heat, TCT will break down to form chlorine gas. An intermediate product of TCT breakdown is nitrogen chloride, which presents a severe explosion hazard when heated or exposed to shock.
Two types of tablets were produced by Advanced Laboratories -- a "quick" tab that was a blend of TCT and soda ash with other chemicals, and a "slow" tab that did not contain soda ash. TCT blended with alkaline materials such as soda ash is subject to more rapid decomposition in the presence of water than TCT alone and produces temperatures sufficiently high to ignite paper products or wood.
Mixing was accomplished on the second floor where the raw materials were stored. Three blenders were in use, two for the Quick Tab product and one for Slow Tab blend. The mixing area on the second floor was called the "Blending Room." The blended mixture was discharged into chutes leading down to the tablet presses (one for each blender) on the first floor in the "Tab Room."
A pneumatic dust collection system was employed to recover products from the blender and discharge areas on the second floor. The dust was deposited in a collection bin on the second floor. Recovered dust and reground broken or defective tablets were saved to be added later, in small amounts, to new batches of raw ingredients in the blenders. This recycled material, called "remix," was stored in paper drums against the (east) wall (see Appendix B). In addition to the remix, approximately 1,000 polyethylene lined paper drums of pure TCT, each weighing 300 pounds, were stored two to three pallets high on the (east and west) sides of the second floor.
The building was equipped with a dry pipe automatic sprinkler system. On the second floor, however, the sprinkler piping had been disconnected by the occupants in the area where the chemicals were mixed. The first floor also had a partial sprinkler system.
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