Ammonia is a troublesome by-product of manure decomposition. It is an eye irritant at levels above 20 to 25 ppm. When exposed to levels around 1,500 ppm, people begin to cough and froth at the mouth. Ammonia is deadly at 5,000 ppm.
Ammonia has a distinct odor, which humans can detect in concentrations as small as 5 ppm. It's common during winter months for ammonia levels to exceed 25 ppm, even under normal winter ventilation rates. Although it is debated by safety experts, 25 ppm is frequently recommended as a maximum acceptable level for ammonia. If your eyes burn when you enter an enclosed livestock facility, you know ammonia levels are at least 20 ppm.
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