If the force measured exceeds the safety force threshold, the operator may require {TAIL ~ the use} of a secondary safety device at {HEAD ~ step} 410 until the force value is measured to be less than the safety force threshold 
If the force measured exceeds the safety force threshold , the operator may require { TAIL ~ the use } of a secondary safety device at { HEAD ~ step } 410 until the force value is measured to be less than the safety force threshold
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH