UL 521
For UL 521, standard title is Heat Detectors for Fire Protective Signaling Systems; nrtl is UL; laboratory is UL LLC; status is currently recognized, recorded from its source on 2026-08-10.
- Test standard
- UL 521 verified
- Standard title
- Heat Detectors for Fire Protective Signaling Systems verified
- NRTL
- UL verified
- Laboratory
- UL LLC verified
- Status
- currently recognized our reading
Values marked our reading are our classification of what the source says — the source does not print them in those words. The quote below is the evidence for each one; judge it yourself.
What the source says
UL 521 | Heat Detectors for Fire Protective Signaling Systems |
— osha.gov, retrieved 2026-08-10
Source
- osha.govhttps://www.osha.gov/nationally-recognized-testing-laboratory-program/ul