From the HP LaserJet II / III Service Manual (same Canon engine as the Laserwriter II series):
"Ozone Emissions:
General - The corona assemblies found in laser printers and photocopiers generate ozone gas (O3) as a by-product of the electrophotographic process. Ozone is only generated while the printer is actually printing (i.e. while the corona assembly is energized). Underwriters (UL) has established a standard for ozone emissions. All LaserJet printers meet this standard when shipped from the factory.
Employer Responsibility - Because ozone can be an irritant, various regulatory agencies have stablished limits to the amount of ozone to which employees may be exposed. The employer should provide a work environment that meets the following standards:
* A person may not be exposed to an average concentration of greater than 0.1 part per million (PPM) of ozone for a period of 8 hours.
* At this time, the American Conference of Governmental Industries Hygienists (ACGIH) has proposed a ceiling limit of 0.1 PPM for ozone
Recommended for Minimizing Ozone Exposure:
Almost all ozone concerns arise from abnormal site or operating conditions. The following conditions may generate an ozone complaint:
* Multiple laser printers in a confined area
* Extremely low relative humidity
* Poor room ventilation
* Printer exhaust port directed toward the faces of personnel.
* Existing ozone filter in need of replacement (see chapter 4)
* Long, continuous printing combined with any of the above conditions
Chapter 4:
Ozone Filter replacement
"... The filter should be replaced every 50,000 pages...Visual inspection will not show that a filter is dirty, page count is the only reliable indicator on which to base a decision to changea filter."
Hmm, this explains why they changed to a charge roller in later models to avoid this ozone "smell". Some people, including myself, complained of feeling lightheaded and now that makes sense. As I recall, it was just a carbon-based filer. We did blow air through them when they were dusty and replaced them if they were crumbling or when a maintenance kit was replaced.
Thanks for the memory lane!