What is the established threshold limit for ammonia in underground mines?

The established threshold limit for ammonia in underground mines is set at 0.005% by volume. This threshold is crucial because ammonia can pose significant health risks to workers in confined spaces. Higher concentrations can lead to respiratory issues, irritation of the eyes, skin, and mucous membranes, and can even impact overall neurological function in severe cases.

Setting the limit at 0.005% reflects the need to maintain a safe working environment and mitigate any potential exposure to hazardous substances. This threshold is established based on extensive research and guidelines from health and safety organizations, ensuring that the working conditions in underground mines are as safe as possible for miners.

The other options represent higher concentration limits that would not be protective of worker health, which is why they are not established thresholds. Adhering to the specified limit helps in maintaining compliance with safety standards and safeguarding miners' health.