Because NH3 boils at −33.34 °C, the liquid must be stored under high pressure or at low temperature. Its heat of vapourization is, however, sufficiently high so that NH3 can be readily handled in ordinary beakers, in a fume hood. 
It is cooled before opening its seal to minimise the pressure. 
When mixed with oxygen, it burns with a pale yellowish-green flame.Anhydrous ammonia is classified as toxic (T) and dangerous for the environment (N). The gas is flammable (autoignition temperature: 651 °C) and can form explosive mixtures with air (16–25%). The permissible exposure limit (PEL) in the United States is 50 ppm (35 mg/m3), while the IDLH concentration is estimated at 300 ppm. Ammonia reacts violently with the halogens. Nitrogen triiodide, a primary high explosive, is formed when ammonia comes in contact with iodine. Ammonia causes the explosive polymerisation of ethylene oxide. It also forms explosive fulminating compounds with compounds of gold, silver, mercury, germanium or tellurium, and with stibine. Violent reactions have also been reported with acetaldehyde, hypochlorite solutions, potassium ferricyanide and peroxides.
						

							
as the ammonia is a volatile liquid and its boiling point is very low , makes its vapour pressure very high so openning the bottle causes the ammonia evaporate and mix with the air .ammonia is very harmful for both our skin and eyes , and for our lungs also . cooling it before openning  makes ammonia liquid. So the damage can be avoided
						

							
"How will ammonia act within the body? once ammonia enters the body as a result of respiratory, swallowing or skin contact, it reacts with water to provide ammonia liquid water. This chemical is incredibly corrosive and damages cells within the body on contact." 
						

							
Te vapour pressureof ammonia at room temperature is very high and hence the ammonia will evaporate unless the vapour pressure is decreased cooling decreases the vapour pressure so that the liquid remains in the same state hence the bottle is cooled before opening