Narrative:

Departed for a personal sight seeing flight with 2 family members. Per SOP; picked up flight following from approach control. Initially held to below 3;000 feet due to traffic; was later cleared by approach control; but decided to continue at that altitude. Pointed out landmarks; highway under construction; golf courses; etc. And was about to mention that I evaluate them for possible emergency landing locations. Just then; noticed billowing smoke/vapor from below instrument panel on right side. Smelled and tasted metallic; but not electrical/fuel/oil based fire. Noticed aircraft was trimmed for straight and level; initially thought engine fire; but noticed no abnormal engine readings or loss of power. Manipulated throttle control and still had full control of engine. Did not know cause and was starting to go through 'smoke in cockpit' items from memory. Notified approach control of smoke in cockpit and was diverting back to my departure airport with the air force base as an alternate. They acknowledged and stood by to offer assistance. At this time; passenger in back said he thought his foot had bumped the fire extinguisher. Visibility in cockpit improved and from past experience as a fire fighter; felt this was a dry chemical discharge and nothing more. Asked my passengers to check their cabin floor for residue; and they confirmed it (1 is a fire fighter as well). From activation of fire extinguisher to identifying it was not an emergency seemed less than 30 seconds. Cabin self ventilated and kept turn back to my departure airport. Notified approach control of what had happened and that we will be returning as a precaution; but no further assistance needed. Per approach control; I knew we would keep on flight following until over the air force base; as my destination is 5 miles east of the air force base. Thanked controller for assistance/ being there during initial alarm when I was handed off to my tower. Upon arrival; had ATIS information whiskey from approximately 5 minutes before handoff; but upon handoff; and on tower frequency; no reply. Then diverted my course to parallel my destination delta airspace (but just outside) and rechecked frequency and then ATIS. Noticed at this time that no ATIS information was broadcast; just normal after hour ASOS reading and announcement the tower was closed. Entered right downwind from a 45 degree entry; looked for any possible light gun signals while broadcasting my intentions on tower frequency/ now unicom. Uneventful landing. Upon normal exit of aircraft; did determine fire extinguisher was activated and contents in cabin. Called owner of aircraft to advice of situation; and assisted in cleanup of aircraft. I had reserved the aircraft for a morning sight seeing flight with other family members; but due to not feeling 'imsafe' being valid any more; decided to cancel the flight and book at a later date.chain of events: I have over 100 hours in this type aircraft; but none in last 5 years. Had obtained a BFR in the aircraft 3 weeks before and this was my first flight since. Used to larger cessna aircraft where it's easier to check fire extinguisher for proper seal and pin placement. Other factors were showing non fliers to aircraft; minor distraction while flying and not totally familiar with this aircraft. I knew the systems and it didn't make sense to get that volume of smoke/fumes from that area.human performance considerations: as with any new situation; especially a rapid and total almost blinding vapor; I was momentarily panicked. Then training kicked in; notified ATC of situation (in case I needed to turn off radios) and did initial check of equipment with no problems noted. I was not to a high time in past 90 days; and the lack of remembering what to do hinder a quick diagnosis. Lessons learned; do expect the unexpected; have an escape route; and when possible be under IFR or VFR flight following. If this was truly serious; I knew my initial call would alert ATC what was going on in case I had to turn off avionics/electrical system. Also truly know the immediate actions items for the plane you will be flying; and always remember aviate; navigate; and communicate.

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Original NASA ASRS Text

Title: A C172 passenger accidentally activated the portable fire extinguisher under the pilots seat with his foot creating what appeared to be a fire. But the extinguishing agent was quickly identified and the flight returned normally to the departure airport.

Narrative: Departed for a personal sight seeing flight with 2 family members. Per SOP; picked up flight following from Approach Control. Initially held to below 3;000 feet due to traffic; was later cleared by Approach Control; but decided to continue at that altitude. Pointed out landmarks; highway under construction; golf courses; etc. and was about to mention that I evaluate them for possible emergency landing locations. Just then; noticed billowing smoke/vapor from below instrument panel on right side. Smelled and tasted metallic; but not electrical/fuel/oil based fire. Noticed aircraft was trimmed for straight and level; initially thought engine fire; but noticed no abnormal engine readings or loss of power. Manipulated throttle control and still had full control of engine. Did not know cause and was starting to go through 'smoke in cockpit' items from memory. Notified Approach Control of smoke in cockpit and was diverting back to my departure airport with the Air Force Base as an alternate. They acknowledged and stood by to offer assistance. At this time; passenger in back said he thought his foot had bumped the fire extinguisher. Visibility in cockpit improved and from past experience as a fire fighter; felt this was a dry chemical discharge and nothing more. Asked my passengers to check their cabin floor for residue; and they confirmed it (1 is a fire fighter as well). From activation of fire extinguisher to identifying it was not an emergency seemed less than 30 seconds. Cabin self ventilated and kept turn back to my departure airport. Notified Approach Control of what had happened and that we will be returning as a precaution; but no further assistance needed. Per Approach Control; I knew we would keep on flight following until over the Air Force Base; as my destination is 5 miles east of the Air Force Base. Thanked Controller for assistance/ being there during initial alarm when I was handed off to my Tower. Upon arrival; had ATIS information Whiskey from approximately 5 minutes before handoff; but upon handoff; and on Tower frequency; no reply. Then diverted my course to parallel my destination Delta Airspace (but just outside) and rechecked frequency and then ATIS. Noticed at this time that no ATIS information was broadcast; just normal after hour ASOS reading and announcement the Tower was closed. Entered right downwind from a 45 degree entry; looked for any possible light gun signals while broadcasting my intentions on Tower frequency/ now Unicom. Uneventful landing. Upon normal exit of aircraft; did determine fire extinguisher was activated and contents in cabin. Called owner of aircraft to advice of situation; and assisted in cleanup of aircraft. I had reserved the aircraft for a morning sight seeing flight with other family members; but due to not feeling 'IMSAFE' being valid any more; decided to cancel the flight and book at a later date.Chain of Events: I have over 100 hours in this type aircraft; but none in last 5 years. Had obtained a BFR in the aircraft 3 weeks before and this was my first flight since. Used to larger Cessna aircraft where it's easier to check fire extinguisher for proper seal and pin placement. Other factors were showing non fliers to aircraft; minor distraction while flying and not totally familiar with this aircraft. I knew the systems and it didn't make sense to get that volume of smoke/fumes from that area.Human Performance Considerations: As with any new situation; especially a rapid and total almost blinding vapor; I was momentarily panicked. Then training kicked in; notified ATC of situation (in case I needed to turn off radios) and did initial check of equipment with no problems noted. I was not to a high time in past 90 days; and the lack of remembering what to do hinder a quick diagnosis. Lessons Learned; Do expect the unexpected; have an escape route; and when possible be under IFR or VFR flight following. If this was truly serious; I knew my initial call would alert ATC what was going on in case I had to turn off avionics/electrical system. Also truly know the immediate actions items for the plane you will be flying; and always remember aviate; navigate; and communicate.

Data retrieved from NASA's ASRS site as of July 2013 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.