Haze machines, or haze generators, commonly referred to as hazers, are similar to fog machines in that they produce droplets suspended in the air which are designed to make light beams visible.
Unlike conventional fog which can be dense enough to become opaque, haze is very thin. Ideally haze is barely noticeable, if at all, in normal lighting conditions. This allows the operator to fill a venue with haze prior to an event without creating a visibly distracting cloud.
Haze also has a substantially longer hang time than conventional fog. While conventional fog may hang in the air for up to 5 minutes, a typical water-based haze can last 1 hour and oil-based haze 6 hours or more, depending on the size of the venue and the amount of ventilation.
Some haze machines use a compressor to atomize a fluid (usually, though not always oil-based), therefore they do not require any warm up time. Other machines use a heater to vaporize the fluid (usually water-based). Most oil-based haze fluids use a mineral oil base, and most water-based fluids use either a glycol or glycerol base.
Quite often Hazers do not set of smoke alarms, but always do tests before you use them if you can.
Tip: When you have finished using your hazer, ensure you run it for at least 5-10 minutes on full fan with no haze output. This will ensure that the jets are clean of any burnt or un-burnt haze fluid.
Adverse effects on respiratory health
Although often believed to be safe to breathe, exposure to mineral oil, glycol and glycerin-based theatrical fogs produced from fog or haze machines have been associated with adverse short and long-term effects on respiratory health in exposed performers and crew members, especially those with respiratory problems (such as asthma). One should therefore avoid breathing generated smoke or fog It is safer to add smoke effects digitally in postproduction of films than to use theatrical smokes on set. Glycol-based fog is associated with headaches, dizziness, drowsiness and tiredness in those exposed. These results would be expected given that glycols share some chemical similarities to alcohols and given the small size of fog particles making it easy for them to enter the bloodstream. Symptoms of wheezing and chest tightness were associated with longterm exposure to theatrical smoke and fogs.
extracted from wikipedia