▁dies el ▁gener ators , ▁and ▁this ▁can ▁translate ▁into ▁enorm ous ▁sav ings ▁across ▁thousands ▁of ▁tele com ▁sites ▁in ▁trop ics . ▁ ▁Fire ▁and ▁safety ▁issues ▁Some ▁phase ▁change ▁materials ▁are ▁susp ended ▁in ▁water , ▁and ▁are ▁relatively ▁non to xic . ▁O thers ▁are ▁hydro car b ons ▁or ▁other ▁fl amm able ▁materials , ▁or ▁are ▁to xic . ▁As ▁such , ▁PC M s ▁must ▁be ▁selected ▁and ▁applied ▁very ▁carefully , ▁in ▁accord ance ▁with ▁fire ▁and ▁building ▁codes ▁and ▁sound ▁engineering ▁practices . ▁Because ▁of ▁the ▁increased ▁fire ▁risk , ▁fl ames p read , ▁smoke , ▁potential ▁for ▁explos ion ▁when ▁held ▁in ▁containers , ▁and ▁li ability , ▁it ▁may ▁be ▁wise ▁not ▁to ▁use ▁fl amm able ▁PC M s ▁within ▁resident ial ▁or ▁other ▁regularly ▁occupied ▁buildings . ▁Ph ase ▁change ▁materials ▁are ▁also ▁being ▁used ▁in ▁thermal ▁reg ulation ▁of ▁electron ics . ▁ ▁See ▁also ▁▁ ▁He at ▁pipe ▁ ▁References ▁ ▁S ources ▁ ▁P H ASE ▁CH ANGE ▁M AT ER IAL ▁( PC M ) ▁B ASE D ▁EN ER G Y ▁ST OR AGE ▁M AT ER IAL S ▁AND ▁G LOB AL ▁AP PL ICATION ▁EX AMP LES ▁ ▁Za fer ▁U RE ▁M . Sc ., ▁C . Eng . ▁M ASH RA E ▁H V AC ▁App lications ▁ ▁Ph ase ▁Change ▁Material ▁Based ▁Pass ive ▁C ool ing ▁Systems ▁Design ▁Princi pal ▁and ▁Global ▁Application ▁Ex amples ▁Za fer ▁U