Adding too much chemical causes an incident

A news report mentions an incident where an orange gas cloud leaked from a manufacturing facility for making ferric sulphate. Apparently, too much nitric acid was added to a batch, resulting in a violent reaction that produced excess amounts of nitrogen dioxide that escaped from the reactor into the air.Nitrogen dioxide is a reddish brown gas and is highly toxic if inhaled and is also corrosive.
Ensure that you have proper controls over addition of chemicals, especially if adding an excess of one chemical can trigger something unwanted. Engineering controls are the best to avoid such mishaps. Depending only on an SOP in such situations may cause an an incident to happen.
Read the article in this link.