The Design of safe Stairs
Information on geometry, slip resistance, illumination and identification
Many things have to be observed when designing stairs. The focus is on ensuring a safe use. The most important requirements are represented here.
- Stairway dimensions and geometries
- Banisters and handrails
- Slip resistance, illumination, and identification
- Stairways along escape and rescue routes
The step measure rule has to be observed when designing safe stairway treads.
Stairway dimensions and geometries
For a smooth sequence of movement on a stairway, its dimensions must orient on the step length. The so-called step measure rule is tried and tested for planning stairways with medium angles of inclination.
a + 2s = SL
a = tread depth
s = rise (incline)
SL = step length
The step measure rule should be applied to stairways with inclinations between 24° and 36°. Values of 59 to 65 cm are decisive as step length. For stairways with medium angles of inclination of 30°, the step length of about 63 cm is most favourable.
In general, the following applies: the steeper the stairway the higher the step length selected should be.
Treads are deemed dimensioned sufficiently if they comply with the following dimensions:
a = 26 … 32 cm
s = 14 … 19 cm
Tread measures of a = 29 cm and s = 17 cm are considered ideal.
For steep stairways with higher angles of inclination or flat flights of stairs, there are different calculation formulae (see publications).
Stairway landings are designed to reduce the physical stress when climbing stairways.
The following rule is applicable: for stairways with medium angles of inclination, a landing must be provided after 18 treads.
The landing depth should correspond to a multiple of the step measure. In this, an odd number of steps should be taken as the basis, since this corresponds to the motion symmetry and the walk rhythm.
A stairway may consist of several stairway runs connected to one another through landings. A differentiation is made between stairways with straight and coiled runs. Stairways with coiled runs are not admissible for certain applications.
Stairway run widths
The run widths of stairways depend on the type of use and the number of users. For stairways leading to permanently used workstations, the minimum width is 1.0 m. Lower dimensions are possible for stairways used rarely that are not required according to Building Law (see "publications"). Larger run widths are necessary for stairways where people could simultaneously be climbing up and down and encounter each other.
Banisters and handrails
Banisters are necessary on the free side of stairway systems; they protect against falling. Furthermore, banisters must provide protection against falling through, for example with the help of a knee rail.
The banister height depends on the vertical drop in each case:
- vertical drop up to 12 m: banister height at least 1.00 m
- vertical drop more than 12 m: banister height at least 1.10 m
However, the Building Law contains partially differing requirements.
As a matter of principle, the following is applicable: if a stairway is also used by children, a child-proof banister design must be made sure, for example for residential buildings or in public buildings.
Children like to climb and are particularly skilful in doing so. Therefore, banister designs with horizontal bracing elements, such as a knee rail, are not particularly child-proof. Banisters with vertical filler elements spaced apart at most 12 cm are safer.
The stairway handrail must be considered as well. It has a supporting stabilisation function in the event of an insecure walk, offers guidance for handicapped people, and should be installed at a height of between 0.80 to 1.15 m. The profile should allow for safely gripping around the handrail, which is why edged flat material is not suitable.
Slip resistance, illumination, and identification
Stairway treads should be characterised by the same slip resistance as the adjacent areas. The slip resistance of the tread surface and the tread edge should be as identical as possible. If anti-slip tread edge auxiliary systems are being used, they should not protrude over the top in order to avoid stumbling. Moreover, the width of the tread edge systems should be selected depending on the stairway inclination.
Likewise, sufficient illumination is important. It is the basic prerequisite for anticipatorily orienting regarding geometry, state, and course of the stairway, as well as for perceiving possible dangerous spots.
Pursuant to the technical rules for workplaces (ASR) A3.4, a light intensity of 100 lx is the minimum requirement inside buildings for traffic routes including stairways (see also table 1). However, there are no separate specifications regarding the illumination of outdoor traffic routes including stairways in the ARS A3.4.
The specified figures are minimum values. If specified by the risk assessment, specifically required higher light intensities must be defined. This is particularly recommendable for stairways along outdoor traffic routes.
The visibility of stairway treads can be increased by colour coding. At least the first and the last tread of a stairway run should be colour-coded. Furthermore, equalizing steps in the course of traffic routes must be identified using a warning sign.
Stairways along escape and rescue routes
Admissible stairway shapes
As a matter of principle, only stairways with straight runs are deemed escape and rescue routes. Coiled and spiral staircases are only admissible along the secondary escape route in reasoned individual cases. This is applicable if the results of the hazard assessment give reason to expect that they will be used safely in the event of a hazard.
Required stairway widths
In ASR A2.3, widths for routes designed for the movement of people within the company are specified. These widths must not be fallen below on stairways either so that the stairways do not turn into "bottlenecks" along the escape and rescue routes.
The usable run width of stairways leading to permanent workstations and of stairways required pursuant to Building Law should be 1.0 m at least.* It should be possible to transport a person lying on a stretcher regarding the width and course of the stairway and the entire staircase.
* Supplemental sheet 1 (Jan. 1997) for DIN 18065 technically introduced the definition of a minimum width of 1.0 m for stairways required pursuant to Building Law as a technical building specification via the building ordinances of the federal states.