PER NFPA FIRE ALARM SYSTEM SMOKE DETECTORS SHOULD BE TESTED ANNUALLY
Photo VS Ion
The Ion detector reacts faster* and is more responsive to smoldering fires that put out small combustible particles of nearly invisible smoke.
The Photo Electric detector is reacts slower* than the ion and is more responsive to flaming fires which put out larger visual particles of black smoke.
With the advances in modern technology, today’s smoke detectors seldom false alarm. However, environmental conditions can cause nuisance alarms. False alarms are alarms caused by faulty detectors. Nuisance alarms are alarms caused by environmental reasons other than smoke. Both Ion and Photo Electric smoke detectors can have nuisance alarms. The cause of these nuisance alarms are different for each detector. Knowing these differences can help in deciding which detector should be used.
Because the Ion detector does not see smoke. It test the air for small combustible particles. These combustible particles can come from sources other than smoke. Some sources are chemicals and paints.
The Photo Electric detector on the other hand needs to see the fire and can be be fooled by dust, steam and spider webs.
Because of the differences in nuisance alarm factors consult with a professional about which detector is best suited for your needs. Always install fire alarm devices per Manufacturer, NFPA and local code requirements.
*Note: The terms faster and slower are relative to controlled testing. In actual field usage the time differences are minimal and for most applications either detector is equal for the purpose of life safety. Also though the photo electric detector is slower it is more stable than the ion detector and less likely to have nuisance alarms.