A researcher working in a laboratory glassware washing area thought she should refresh the bleach solution for soaking lab glassware. In an "inattentive moment" she added fresh bleach to what she thought was the bleach soaking tub; unfortunately the tub did not contain bleach but contained 5% hydrochloric acid. The acid solution (with bleach) immediately turned from clear to yellow. She quickly realized that bleach and acid should never be mixed because toxic chlorine gas can be created. She immediately had everyone leave the room; she considered calling 911, but since everyone was safe and there was no chlorine odor in the hallway she called EH&S (510) 642-3073, to get further advice.
In this case, it seems that very little if any chlorine gas was created. There was no observation of a dense green or brown cloud of chlorine gas as might be expected. This may have been a result of a well ventilated laboratory. EH&S considers this accident to be a near miss; if more bleach had been added, the outcome could have been worse. It is also a reminder that the mixing of bleach with some household cleansers (e.g. toilet bowl cleansers that contain acid) can generate chlorine gas, and mixing bleach with ammonia generates toxic chloramine vapor.