Sources for heter (I can’t link to Tzitz Eliezer, but I can link to some of his sources):
http://www.hebrewbooks.org/pdfpager.aspx?req=14561&st=&pgnum=48
http://www.hebrewbooks.org/pdfpager.aspx?req=1902&st=&pgnum=81&hilite=
http://www.hebrewbooks.org/pdfpager.aspx?req=40774&st=&pgnum=29