Abstract: A safety system for a gas cylinder valve stem includes a coupler and a handwheel. The coupler includes a first engagement mechanism (EM). The coupler is configured to: mount onto the stem's base; and rotate the stem in unison with rotation of the coupler or remain stationary in unison with the stem. The handwheel includes a second EM configured to engage in surface-to-surface contact with the first EM. A locking mechanism is defined by the first and second EMs. The handwheel is configured to mount onto the stem's intermediate portion between the stem's tip and the coupler's proximal top surface. The handwheel is configured to rotate about the stem's longitudinal axis, in response to receiving an angular force of rotation in a lateral plane. The handwheel rotates in unison with the coupler when the locking mechanism is engaged, yet rotates independent from the coupler when the locking mechanism is disengaged.