A chemical leak at Milk Specialties in Fond du Lac, Wis. caused a temporary evacuation on Thursday. A large yellow plume was seen above the plant at one point. Fire Chief O’Leary said “Although the exact concentration and type of gas is not known, it’s believed to contain chlorine. One of the concerns we have is what the wind is doing on days like today. When the air is thick and there’s little wind it’s actually harder because those vapors end up not dissipating in the atmosphere as fast. It’s tedious work. It takes time because these hazardous materials incidents if you make a mistake it could be a fatal one, so we do a lot of things out of precaution and safety being number one.” The cause of the leak is currently under investigation.