In human resources the irritation threshold is the

The right answer is a point at which a person notices something and becomes annoyed.  

In science, a threshold effect refers to the appearance of a phenomenon from a certain value of a variable.

In psychology, irritability is a trait of a character indicating a propensity for angry reactions.

So the threshold of irritability designates the appearance of an angry reaction from a determined intensity of stimulation (below this value, there is no reaction).

enhanced global partnerships and exploration capabilities may advance international preparedness for protecting the earth from catastrophic events such as some asteroid strikes, advancing collaborative research on space weather and protecting spacecraft by developing new means for space debris removal.