Standards for emergency stopping rates of web handling equipment are not prescribed. There is a standard that calenders must stop in the distance between the finger-tip and shoulder. This is untenable in 2018. We can and must do better.
A few comments about safety and stopping.
- Standards for E-Stop have not changed in decades.
- Guarding and guard interlocks are more important than E-Stop. This is because the guarding prevents an injury and E-Stop limits an injury already underway. Guarding standards become more rigorous every year.
- The E-Stop function is required by all current standards in addition to guarding.
- The guard interlocking will initiate the same type of safety stop and E-Stop in almost all cases. Stopping types are defined in NFPA 79, ISO 13850 as Category 0 (Coast Stop), Category 1 (Regenerative stop for a period of time followed by coast stop). Adding a mechanical brake is sometimes required in particularly hazardous applications (elevators and mine hoists).
- The stopping time is one of the variables in the calculation of safe distance (if light curtain, scanner, etc. is used). Generally, the e-stopping time for web handling equipment will result in a need for locking guard interlocks – subject to a risk assessment.
- Generally drives used in web handling are underpowered in term of providing an emergency stop fast enough to be protected with a light curtain (or similar device)
- It is sometimes possible to provide quick enough stopping times during threading if thread speed is limited (again using the required safety category to ensure the speed is limited).
My best professional advice is to provide a Control Reliable e-stop but do an excellent job engineering the guarding and interlocking. Include a written risk assessment – what are the hazards? What category or Performance Level of guarding and guard interlocking is required? Include a safe distance calculation if light curtains, mats, scanners are used.