C. F. Keil and Franz Delitzsch on Numbers 19:14-16

Num 19:14-16

Special instructions concerning the defilement. If a man died in a tent, every one who entered it, or who was there at the time, became unclean for seven days. So also did every “open vessel upon which there was not a covering, a string,” i.e., that had not a covering fastened by a string, to prevent the smell of the corpse from penetrating it. פּתיל, a string, is in apposition to צמיד, a band, or binding (see Ges. §113; Ewald, §287, e.). This also applied to any one in the open field, who touched a man who had either been slain by the sword or had died a natural death, or even a bone (skeleton), or a grave.