Two people suffered from headaches and nausea, and employees were evacuated Tuesday after an ammonia gas leak at Maui Soda & Ice Works in Wailuku, Maui firefighters said.

Firefighters responded to the hazardous materials call at about 11:30 a.m. and found the gas leaking from a room that housed the gas storage tanks on Lower Main Street.

Employees evacuated and nearby businesses that called to report the strong smell of the gas were advised to shelter in place and close all windows, a Maui Fire Department spokesman said.

Two people were checked by paramedics for headaches and nausea and were released at the scene.

Firefighters found a relief valve had activated, releasing excess pressure due to overheated equipment. Air quality returned to normal around noon.

Anhydrous ammonia is commonly used as a refrigerant in larger commercial applications and is detectable by its pungent odor.