There are various levels of how a two-hand control safety system can perform, depending on the hazard posed by the machine. ISO 13851 segments Type III in accordance with ISO 13849-1 categories.

Type III A

Require simultaneous actuation of both buttons during hazardous motion of the machine

Release of one or both hand controls will stop the machine

Meets Cat 1 per ISO 13849-1 (EN 954-1)

Type III B

Type III A requirements plus

Restarting machine is possible only if both buttons have been released

Meets Cat 3 per ISO 13849-1 (EN 954-1)

Type III C

Type III B requirements plus

Both start buttons must be activated within 500 milliseconds of one another

Meets Cat 4 per ISO 13849-1 (EN 954-1)