Hawkins is routinely appointed to analyze the reason for fires occurring at farms. This explicit case examine discusses some uncommon points that prompted an exothermic response, and pertains to the usage of calcium oxide (also called quicklime), as an animal-friendly sanitization product. Calcium oxide is most frequently used within the type of a white powder, made out of the thermal decomposition of supplies like limestone and seashells. It may be used to disinfect and sanitize, as a result of it creates a dry atmosphere the place micro organism is not going to thrive. It is usually typically utilized in agricultural settings as a fertilizer and soil conditioner. Quicklime has beforehand been used as a weapon of battle, it’s thought to have been one of many elements of Greek Fireplace. Through the reign of Henry III, the English Navy destroyed an invading French fleet by blinding them with clouds of quicklime. In fiction, Bernard Cornwell’s nineteenth Century hero, Richard Sharpe used quicklime that he made by burning oyster shells, to stave off the French military (Sharpe’s Siege).
Background info and discovery of the hearth
Earlier than Hawkins carried out an examination of the constructing, the circumstances of the incident have been mentioned with the 2 staff who found the hearth:
The hearth occurred in a wood constructing, which housed laying hens, and had an open-air veranda on one facet.
At roughly 14:30, the 2 staff cleared the birds from the veranda, after which unfold a bag of calcium oxide over the ground of the veranda to disinfect it. They then put recent straw over the ground earlier than letting the birds again onto the veranda. Lastly, the employees left the constructing to hold out work elsewhere.
At 17:00, one of many staff observed smoke coming from the veranda of the constructing. He went to analyze and noticed smoke and flames on the north-western nook of the veranda.
Although there have been electrical lights within the veranda, these have been switched off on the time of the hearth. The employees stated there had neither been latest work on, nor issues with, the mounted wiring within the constructing.
One of many staff was a smoker, however he said that he didn’t smoke contained in the buildings.
Investigation
Harm attributable to direct hearth assault was restricted to the veranda.
The hearth injury contained in the veranda
I famous a number of piles (roughly 20 cm in diameter) of a white powder amongst the straw within the veranda. I didn’t discover any smoker’s supplies within the space of fireside injury, nor did I discover any across the different farm buildings.
The piles of white powder (indicated by arrows)
Quicklime shouldn’t be usually thought-about a hearth hazard, however calcium oxide will react violently with moisture and provides off warmth (an exothermic response). It was initially unclear, nevertheless, whether or not enough warmth may very well be generated by such an exothermic response to ignite the straw.
I carried out checks to evaluate if the exothermic response of calcium oxide and water might ignite straw. A layer of fresh, dry straw was positioned on a metallic tray. A pile of 500g of calcium oxide was positioned on the straw, after which 500ml of water was added. A layer of straw was positioned on high of this; there have been 4 temperature sensors (Channels 1 – 4) inside the highest layer of straw.
Determine 1 reveals the temperatures recorded throughout this check. The temperature of Channel 1, Channel 3 and Channel 4 elevated quickly as soon as water was added to the calcium oxide. Channel 3 and Channel 4 reached a most of roughly 100°C after which plateaued, whereas Channel 1 continued to rise till it reached roughly 370°C, about 9 minutes after water was added. Initially steam got here from the straw, however this quickly subsided.
Determine 1: Time – Temperature plot (Channel 1-4 probes have been positioned within the straw layer above the calcium oxide)
Roughly eighteen minutes after the water was added “crackling” was heard coming from the straw, and smoke started to appear. I eliminated the highest layer of straw and noticed that the straw beneath it was blackened. Nevertheless, transferring the highest layer of straw allowed air to achieve the blackened straw, and prompted it to glow. A flaming hearth shortly developed.
The blackened straw 18 minutes after water was added to the calcium oxide
Exposing the glowing straw to open air prompted a flaming hearth to quickly develop
Conclusions
The checks confirmed that calcium oxide, when combined with water, reacts exothermically, and represents a viable ignition supply for the straw bedding materials on the veranda.
Once I reviewed the directions supplied with the calcium oxide, I observed that they didn’t particularly point out the danger of fireside. Nevertheless, the directions did stipulate that the product should be unfold evenly, and that the bottom needs to be wetted previous to remedy.
If the calcium oxide had been unfold evenly onto a pre-wetted floor, the exothermic response would have occurred quickly, and warmth would have been misplaced to the environment. The farm staff’ failure to unfold the calcium oxide in a manner that may guarantee a fast response was then compounded by the position of straw on high of the calcium oxide. This lowered the quantity of warmth misplaced to the environment, and as a substitute offered a readily ignitable materials.
Hawkins has ready a letter for the producers, which detailed these findings and recommended that producers of fast lime evaluate the recommendation supplied with the product–highlighting the necessity to unfold the calcium oxide evenly to cut back the danger of fireside.
Dr Ian Tatner is a Chartered Engineer (CEng) with a PhD in Corrosion Fatigue of Stainless Metal. Although his profession started within the offshore oil and fuel pipeline set up trade, Ian joined Hawkins in early 2009, and has been investigating fires and explosions, in addition to pedestrian falls, ever since. He has seen a broad vary of instances from fires in home properties, to extra complicated car fires and manufacturing facility explosions. Ian has additionally investigated quite a few pedestrian falls in each private and non-private buildings. Ian is a Senior Affiliate based mostly in our Leeds Workplace.
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