To answer Gayle's question: Yes I always fired at night. The earlier kilns (I taught 35 years) had timer shut off's, so I would set the timer for 8 hours, and it would shut off. The time of 8 hours was found out by experimentation. The later kilns had computerized timers and would do it all automatically. Only had 1 incident in all that time, and that was when a new teacher had put a board with ceramics on top of the kiln after I left school, not paying attention to the kiln being on, and the board started smoking. We tried to let our custodial staff know we were firing so that they were aware it was on overnight.
To make my point, I did not get a proper ventilation system in my classroom until after I came back from cancer surgery and chemotherapy, at which time the school system allowed me to have the author of Artist Beware come and evaluate our art rooms and present a report to them. My cancer, most probably wasn't a result from art supplies, was the catalyst for my concern, and I was "placed" in a study of art teachers.
One of the things I realized was that there are many art experiences one can give our students without jeopardizing our and their health. For example we used to teach jewelry casting without proper ventillation, we used to do printmaking with oil based inks, we used to use dyes in our textile classes, and melted waxes on hotplates for batik. We rewrote our curriculum to eliminate those products, and changed the experiences. I realized for example we were not an "arts high" with extensive art studios, but just an art teacher with one all purpose room which included the kiln.