The comfort rule and safety rule, which were often cited in the past, are now found only in Austrian standard OENORM B 5371, as a note under Point 4.4 regarding the ideal dimension. They are not mandatory, but they are still helpful.
In some locations, it is not possible to build stairways with the ideal pitch ratio of 17:29. In such cases, the comfort rule can be used to check the pitch ratio.
Going – rise = 12 cm pitch ratio
This applies to stairways with a pitch of around 30º degrees and is best suited to stairways with rises of between 16 and 18 cm.
Examples of pitch ratios as per this rule are: 15:27, 16:28, 17:29, 18:30, 20:32. The ratios 16:28 and 17:29 are roughly equivalent to a 30º pitch.
The safety rule produces a pitch ratio between those generated by the step-length rule and the comfort rule.
Going + rise = 46 cm
This rule can be applied to all pitches and still produces good goings even for steep stairways.
Examples of pitch ratios as per this rule are: (shown as rise:going) 15:31, 16:30, 17:29, 18:28, 20:26. The ratio 20:26 is roughly equivalent to a 38º pitch.