Six undergraduate students were exposed when a plastic container of waste chemicals ruptured in a Chemistry Annex teaching lab at around 4 p.m. Tuesday, according to an email Jonathan Sweedler, director of the School of Chemical Sciences, sent to SCS faculty, staff, postdoctoral and graduate students.

As a safety precaution, five of the exposed students used a safety shower and were taken to a medical facility. One of the students reported having a chemical burn on their nose, campus spokeswoman Robin Kaler said in an email.

Kaler also said a sixth student reported a minor irritation on their face to at TA a few hours later.

The investigation of the exact cause of the chemical reaction is ongoing, but initial findings show that a waste container exploded due to a buildup of excessive pressure.

“The Division of Research Safety believes the reaction was caused by nitric acid mixing with a reducing agent to produce a nitrogen oxide gas,” Kaler said in the email. Two containers of ammonium hydroxide broke due to the rupture, releasing ammonia gas into the air, she added.

Students were able to retrieve their belongings from the lab later that night, and the lab was opened for classes on Wednesday.

Kaler also stated in the email that “To prevent something like this from happening again, the laboratory instructors have removed nitric acid from this experiment pending a more detailed review of the laboratory’s objectives and whether the use of nitric acid is necessary for those objectives.”