I found the following information in NFPA 76
Recommended Practice for the Fire Protection of Telecommunications Facilities 2002 Edition
9.1.3.2 Where portable space heaters are necessary for work activities or due to extraordinary problems with HVAC, they should include the following features:
(1) Electrically powered
(2) Listed
(3) De-energized upon tilt or tipover
(4) Illuminated “power-on” pilot light
(5) Variable temperature control
(6) Building management approval
(7) Limited to temporary use of no more than 7 consecutive days
I thought that these rules made sense and offer them here for your review.