Officials are trying to determine how thousands of gallons of a dangerous gas – one that can cause deadly chemical burns to a person's lungs – leaked at a fertilizer plant in southern Minnesota Monday.

Fifteen homes in Clarks Grove (a town of about 700 residents) were evacuated around 11 a.m. Monday, KIMT reports, after the 9,000 gallons of anhydrous ammonia leaked into the air.

The Albert Lea Tribune says the leak was discovered in the tank of a semi, while Clarks Grove Fertilizer LLC. was executing a "conversion" process.

Anhydrous ammonia is described by the North Dakota health department as having a pungent smell, and can cause burning of the nose and throat if even small amounts are inhaled; larger doses can lead to choking, and death from a swollen throat or chemical burns in the lungs.

The dangers of the chemical were written about after the high-profile fertilizer plant explosion outside Waco, Texas, that killed 15 people and injured more than 100 others. National Geographic reported anhydrous ammonia is used to create some of the fertilizers frequently used today. While it's cheap to make, it requires a lot of precaution to store and contain, and if it leaks it can quickly cause severe injuries.

It's a cousin of the long-used ammonium nitrate, National Geographic says. The Guardian, looking at the past 92 years, counted 17 unintended explosions involving ammonium nitrate that resulted in at least one death.

In Clarks Grove Monday, those evacuated from their homes were able to return in the early afternoon, after the air was tested. Nobody was injured.

ABC 6 reports officials with the Minnesota Department of Agriculture were in Clarks Grove Monday evening to investigate what went wrong.