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Stairways, Ramps and Platforms

June 10, 0201

Stairs

The material in this post is extracted from Chapter 10 — Safety in Design — of the book Plant Design and Operations.

An overview of the design requirements for stairs, ramps and platforms are provided in this section; fixed ladders are discussed in the next section. The material here does not provide detailed guidance regarding the measurements and specifications — such information can be obtained from the many of the standards and regulations that cover these items.

Ramps are used in areas where there is high traffic and/or frequent use of wheeled carts that are used to move equipment. Ramps will be used where the elevation change is small and there is sufficient room to allow for a gentle slope.

Stairs should generally be used over ladders in the following situations:

  • When routine movement between two levels is required;
  • For routine tasks such as gauging, inspection and maintenance;
  • Employees could be hand-carrying heavy or bulky tools and/or equipment.
  • There is a potential for exposure to hazardous materials at the elevated location and immediate escape is required.

Regulations and Standards

The design of stairways, ladders and ramps is covered by many regulations and standards, some of which are listed below. These standards provide considerable detail to do with topics such as the spacing between stair treads and the height of hand rails.

  • ANSI A64.1-1968
  • ASTM F 1166 – 95a, Standard Practice for Human Engineering Design for Marine Systems, Equipment and Facilities, 1995.
  • ABS Guidance Notes on the Application of Ergonomics to Marine Systems, January 1998.
  • DOT/FAA/CT-96/1, Human Factors Design Guide for Acquisition of Commercial-Off-The-Shelf Subsystems, Non-Developmental, and Developmental Systems, January 15, 1996.
  • MIL-STD-1472F, Department of Defense Design Criteria Standard, Human Engineering, 23 August 1999.
  • MIL-HDBK-759C, Department of Defense Handbook, Human Factors Engineering Design Guidelines, 31 March 1998.
  • OSHA 1910.24. Walking-Working Surfaces. Fixed Industrial Stairs.

Terminology

Figure 10.1 illustrates some of the terms used in the design of stairs.

Figure 10.1
Stair Terminology

Stair Nomenclature

The following terms are shown in Figure 10.1.

Angle of Ascent / Inclination. The angle of ascent for stairways should be in the range 30 to 50° and the vertical elevation should exceed 24 in. (610 mm.).

Stair rail. The rail on the stair sides used to provide balance when ascending or descending.

Handrail. The rail provided on the open side of an elevated flat walking or working surface to protect workers from falling to a lower surface. It is also called a guardrail.

Riser. The height from one tread to another. They should be spaced equally, and the first or bottom tread should be the same height above the walking surface as the risers are from one another.

Tread. The step on which workers stand. The tread depth should be consistent for a given set of stairs. The top tread should be on the same level as the adjacent walking surface.

Overhead Clearance. A minimum height between each stair tread and any obstruction directly overhead should be specified.

Stair Width. Stairs that are designed for two-way traffic, that are an emergency egress route or that may require stretcher access should be 44 in. (1120 mm) or more in width. One-way stairs that are infrequently used and that do not require stretcher access should be 30 in. (760 mm) or more in width.

Spiral / Winding Stairs

Spiral stairs should not generally be used. Winding stairs can be installed on tanks and similar round structures where the diameter of the structure is not less than about 2.5 meters. The stair should ascend in a clockwise direction to allow the stair rail to be on the right-hand side during descent. A stair rail between the tank and stairs is required if the gap between the tank/tank insulation and stairs is greater than 6 inches (CAL OSHA specifies 8 inches). Intermediate landings are not required.

In areas with significant snow the stairway should be on the sheltered side of the tank.

Landings

If a stair has a vertical rise of 20 ft. or more intermediate landings should be provided every 12 ft. (Occasional use stairways may not require intermediate landings.) The landings should be as wide as the stairs and should have handrails.

Where doors or gates open directly on a stairway, a platform should be provided; the swing of the door should not reduce the effective width to less than 20 inches.

Design Load

Stairways should be built to carry five times the normal anticipated live load, but not less than a 1000 lbs. moving concentrated load. The design load for walkways and platforms should be the maximum probable loads produced by the intended use. The design load should be increased as necessary for any machinery or equipment which may add to the live load.

Stair Rails

Railings are required for floors and stairways that have open sides, and for platforms that have a significant elevation over the deck/grade around them. The following guidance to do with the design of stairs is provided.

  • A single-tier stair rail is used to maintain balance while going up or down stairs, and should be installed on the enclosed side of stairs.
  • A two-tier rail, used to maintain balance and prevent falls from stairs, should be installed on all open sides of stairs.
  • Stairs with three or more steps should be equipped with stair rails.
  • Stairs wider than 88 in. (2240 mm) should be equipped with a single-tier stair rail in the center.
  • Stair rails should be highly visible, often of a different color from the stairs themselves.
  • Toeboards are required if a person could slip under a railing.

Stair Treads

Each tread should be painted to make its leading edge visually distinctive from the color of the rest of the tread or the walking surfaces to which it is connected. When the stair tread and/or deck grating is yellow the leading edge should be painted a bright red. When the stair treads and/or deck grating is galvanized steel or painted a gray color, the leading edge should be painted a bright yellow.

All treads should be slip resistant; steel stairs should have treads made of serrated grating. If floor plate is used then weep holes for drainage should be provided.

Ramps

Ramps are used to minimize tripping hazards and to facilitate use of wheeled equipment such as some fire extinguishers, oxygen/acetylene rigs and hand carts.

Ramps can be used if the angle of inclination is less than 20° (15° preferred) and the change in vertical elevation is less than 24 in. The 24 in. limit may not apply if the ramp is a primary means of access/egress in an emergency and a ramp would more efficiently allow egress. Nevertheless, the 20º angle of inclination limit should still be maintained.

Ramps should have a non-skid surface if the angle of inclination is greater than 10° and should be provided with handrails on the open side of the ramp if the vertical distance from the ramp to the nearest surface is greater than 24 in. (610 mm).

Ramps should have a minimum width of 36 in. (950 mm) and should have landings at the top and the bottom. The landings should be at least as wide as the ramp. There should be adequate space at the landings for people and the equipment that they are carrying or moving to change direction.

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