These requirements cover heat detectors for fire protective signaling systems intended to be installed in ordinary indoor and outdoor locations in accordance with the Standard for Automatic Fire Detectors@ NFPA 72E. Heat detectors covered by these requirements employ either normally open contacts or normally closed contacts@ provide an electronic signal@ or consist of a heat-sensitive cable. The requirements do not cover heat detectors for journal-alarm or unit-alarm devices. Deleted October 3@ 2002
UL 521 BULLETIN-2008 history
2021UL 521-2021 UL Standard for Safety Heat Detectors for Fire Protective Signaling Systems COMMENTS DUE: FEBRUARY 18, 2008
2017UL 521 BULLETIN-2017 UL Standard for Safety Heat Detectors for Fire Protective Signaling Systems (COMMENTS DUE: August 2@ 2017)
2016UL 521 BULLETIN-2016 UL Standard for Safety Heat Detectors for Fire Protective Signaling Systems (COMMENTS DUE: SEPTEMBER 26@ 2016)
1970UL 521-2016 UL Standard for Safety Heat Detectors for Fire Protective Signaling Systems COMMENTS DUE: FEBRUARY 18, 2008
2015UL 521 BULLETIN-2015 UL Standard for Safety Heat Detectors for Fire Protective Signaling Systems (COMMENTS DUE: MARCH 16@ 2015)
2014UL 521 BULLETIN-2014 UL Standard for Safety Heat Detectors for Fire Protective Signaling Systems (COMMENTS DUE: MAY 23@ 2014)
2010UL 521 BULLETIN-2010 UL Standard for Safety Heat Detectors for Fire Protective Signaling Systems
2009UL 521 BULLETIN-2009 UL Standard for Safety Heat Detectors for Fire Protective Signaling Systems (COMMENTS DUE: November 02@ 2009)
2008UL 521 BULLETIN-2008 UL Standard for Safety Heat Detectors for Fire Protective Signaling Systems (COMMENTS DUE: FEBRUARY 18@ 2008)
2001UL 521 BULLETIN-2001 UL Standard for Safety Heat Detectors for Fire Protective Signaling Systems
1999UL 521-1999 UL Standard for Safety Heat Detectors for Fire Protective Signaling Systems Seventh Edition; Reprint with Revisions Through and Including July 20, 2005
1993UL 521-1993 UL Standard for Safety Heat Detectors for Fire Protective Signaling Systems (Sixth Edition)