Calcium oxide and its exothermic reaction
Hawkins was often appointed to investigate the causes of farm fires. This particular case study discusses some unusual aspects that lead to exothermic reactions and relates to the use of calcium oxide (also known as quicklime) as an animal-friendly disinfection product. Calcium oxide is most often used as a white powder and is made from the thermal decomposition of materials such as limestone and shells. It can be used for disinfection and disinfection as it creates a dry environment where bacteria do not grow. It is also often used as a fertilizer and soil conditioner in agricultural Settings. Quicklime was previously used as a weapon of war and is thought to have been a component of Greek fire. During the reign of Henry III, the British Navy covered the invading French fleet with clouds of quicklime and destroyed them. In the novel, Bernard Cornwell's 19th-century hero, Richard Sharpe, uses quicklime he made from oyster shells to avoid the French army (Sharpe's siege).
Before Hawkins inspected the building, he discussed the incident with the two workers who discovered the fire:
The fire broke out in a wooden building with laying hens and an open balcony on one side.
At about 14:30, two workers cleaned up the birds on the balcony, and then spread a bag of calcium oxide on the balcony floor for disinfection. Then they spread fresh straw on the floor and let the birds return to the balcony. Eventually, the workers left the building to work elsewhere.
At 17:00, a worker noticed smoke coming from the balcony of the building. He went to investigate and saw smoke and flames at the northwest corner of the balcony.
Although there were electric lights on the balcony, they were turned off at the time of the fire. Workers said the fixed wiring in the building had not been working or problematic recently.
One of the workers was a smoker, but he said he did not smoke in the building.
Direct fire damage was limited to the balcony.
I noticed several piles (about 20cm in diameter) of white powder in the straw on the balcony. I didn't find any smoker's material in the fire-damaged area, nor did I find anything around the other farm buildings.
Quicklime is not generally considered a fire hazard, but calcium oxide reacts violently with water and emits heat (exothermic reaction). However, it was initially unclear whether this exothermic reaction would produce enough heat to ignite the straw.
I ran tests to assess whether the exothermic reaction of calcium oxide and water would ignite the straw. A layer of clean, dry straw is placed on metal trays. Put a pile of 500g calcium oxide on the straw, then add 500ml water. Put a layer of straw on top; Inside the top layer of the straw are four temperature sensors (channels 1-4).
After about 18 minutes of adding water, the straw made a "crackling" sound and began to smoke. I removed the top layer of straw and found that the straw beneath it had turned black. However, moving the topmost straw puts air in contact with the blackened straw and makes it glow. The fire spread rapidly.
