There is no standardised speed at which we can safely assume that the hazard arising from that speed can always be detected on time.
However, there are some limit values, in VDI 2854 for example, which say that where there are hazardous movements with no pinch or shear points, then speed should be limited to 15m/min. Where there are hazardous movements with pinch and shear points, then 2m/min must not be exceeded.
Please note: These values may be defined differently by other Type C standards and so must be reviewed on a case by case basis.