A neighborhood swimming pool became a hazardous materials clean-up zone after a chemical spill on June 25.

According to the Boise fire department, the incident happened at the Fairmont Pool in Boise, Idaho, when two pool chemicals were inadvertently mixed together during a delivery. The reaction of the two chemicals, (not named) resulted in a gas that caused several people in the area to feel sick. The incident injured 28 people who were treated at the scene and 14 others were taken to the hospital, treated and released.

Boise Fire Division Chief Paul Roberts said a commercial truck was filling chemical tanks for the pool.

Hazardous materials crews were sent to the pool around 1 p.m., and approximately five minutes after the spill. Authorities warned people to “shelter in place” for a few hours because of respiratory injury risk.

Responding crews included 5 fire engines, 2 battalion chiefs, 2 division chiefs, a hazmat team, Ada County paramedics, and Boise police officers worked to control the scene and block traffic.