B737-800 captain reported the portable cockpit fire extinguisher self-discharged at cruise altitude.

Attributes
ACN	1495432
Time
Date	201711
Place
Locale Reference	ZZZ.Airport
State Reference	US
Aircraft 1
Make Model Name	B737-800
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Flight Plan	IFR
Component
Aircraft Component	Portable Extinguisher
Person 1
Function	Captain Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Aircraft Equipment Problem Less Severe

Narrative:

While at cruise; the cockpit fire extinguisher discharged without any provocation. It was secured in its rack behind the first officer's seat. I placed my hand over the top of the extinguisher and quickly opened the cockpit door; handing it to a flight attendant to be wrapped in a blanket. A very loud pressure release was heard and felt from where the plastic top meets the metal tank. Thankfully; it was only an air release. Had the white halon released; there would have been potential for an instant problem in the cockpit. There is currently a recall of kidde fire extinguishers. I wonder if this is included on their list?

Original NASA ASRS Text

Title: B737-800 Captain reported the portable cockpit fire extinguisher self-discharged at cruise altitude.

Narrative: While at cruise; the cockpit fire extinguisher discharged without any provocation. It was secured in its rack behind the First Officer's seat. I placed my hand over the top of the extinguisher and quickly opened the cockpit door; handing it to a Flight Attendant to be wrapped in a blanket. A very loud pressure release was heard and felt from where the plastic top meets the metal tank. Thankfully; it was only an air release. Had the white halon released; there would have been potential for an instant problem in the cockpit. There is currently a recall of Kidde Fire Extinguishers. I wonder if this is included on their list?

Data retrieved from NASA's ASRS site 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.