This article is about Fixed Ladders, Stairs, and Railings Design Technical Requirements in petrochemical plants.
| 1. | Purpose |
| 2. | Scope |
| 3. | Related Documents |
| 4. | Philosophy |
| 5. | General |
| 6. | Ladders |
| 7. | Stairs |
| 8. | Railings and Opening Guards |
| Table 1 | Permissible Range of Rise/Tread Run Ratio |
| Figure 1 | Pitch Range for Fixed Ladders, Stairs, and Inclines |
| Figure 2 | Application for Fixed Ladders |
1. What is purpose of this article? This engineering standard establishes the minimum requirements for the design of fixed ladders, stairs, railings, and opening guards necessary for people to move safely between operating areas of different heights within the plant. The requirements listed herein are drawn primarily from OSHA 29 CFR Part 1910 and are for industrial type applications such as access and maintenance platforms. Requirements of certain building codes may have different constraints than those listed herein and may govern in building type applications.
2. Fixed Ladders, Stairs, and Railings Design Technical Requirements
3. Related Articles, International Codes and Standards
309710D Standard Ladders and Safety Gate
309711D Standard Stairs
309712D Standard Railing
309725D Standard Ladders and Safety Gate (Metric)
309726D Standard Stairs (Metric)
309727D Standard Railing (Metric)
309753D Standard LNG Heat Exchanger Ladder and Railing Details
3CS04002 Compressor Buildings and Structures
Field-Erected, Flat-Bottom, LOX and LIN Storage Tanks
Fabrication of Miscellaneous Metals
American National Standards Institute (ANSI)
ANSI A14.3 Safety Requirements for Fixed Ladders
American Society of Safety Engineers (ASSE)
ASSE A1264.1 Safety Requirements for Workplace Floor and Wall Openings, Stairs, and Railing Systems
U. S. Department of Labor – Occupational Safety and Health Administration (OSHA)
Occupational Safety and Health Standards for General Industry (29 CFR Part 1910) Part 1910.21 Definitions
Part 1910.22 General Requirements
Part 1910.23 Guarding Floor and Wall Openings and Holes
Part 1910.24 Fixed Industrial Stairs
Part 1910.27 Fixed Ladders
4. PHILOSOPHY
- The requirements of OSHA and ANSI are incorporated into or exceeded in this standard. State and local codes shall have preference when they exceed the requirements of this standard.
- Each Company requirements might exceed ANSI and OSHA requirements in some areas (e.g., ladder cage length, safety-gate configurations and clearance distance behind ladder). Supplier interpretations of OSHA standards vary significantly and might lead to unsafe designs often unacceptable to OSHA inspectors. It is imperative that the supplier conforms completely to the specific details of design as shown on the Civil/Structural Standard Design Drawings to ensure uniformity throughout each plant.
5. GENERAL
- Fixed stairways and ladders shall be provided so that employees have a safe means of access between levels.
- Company engineering documents 3CS04002 and 4WEQ-1516 outline some of the specific applications for fixed stairs and ladders. However, when the selection of a stair or ladder is left to the designer’s discretion, the designer shall consider the requirements of this standard and current plant operating practices.
- Fixed stairs shall be provided for access from one structure level to another where operations necessitate regular travel between levels, and for access to operating platforms at any equipment that requires routine attention during operations. Fixed stairs shall also be provided in the following instances: where access to various elevations is required daily (or at each shift) for such routine activities as gauging, inspection, or regular maintenance; where such work may expose employees to acids, caustics, gases, or other harmful substances; or where the carrying of tools or equipment by hand is normally required.
- Spiral stairways will not be permitted, except for special limited usage and secondary access situations where it is not practical to provide a conventional stairway. Winding stairways may be installed on tanks and similar round structures when the diameter of the structure is not less than 5 feet.
- The fixed stairs described in this standard do not apply to a stairway that will be used solely for fire exit purposes. The designer shall consult the governing building code (local, state, or national) for specific design requirements.
- This standard does not apply to stairs used in construction or to articulated stairs where the angle of pitch changes with the rise and fall of the base support.
- Fixed ladders may be used as the primary or secondary access to operating platforms provided the other requirements of this standard are met. Generally, ladders are used as the primary access to platforms on equipment such as cold boxes and column cans. Ladders shall be used only in a vertical position (90 degrees from the horizontal), and their use in any other position will require review and approval by Engineering Safety.
- Fixed ramps or inclines are generally not used for access to operating platforms. However, their use may be permitted in unique situations. See Figure 1.
- The designer shall use the table and figures listed below as a guide in preparing the design drawings.
- Table 1, Permissible Range of Rise/Tread Run Ratio
- Figure 1, Pitch Range for Fixed Ladders, Stairs, and Inclines
- Figure 2, Application for Fixed Ladders
- Materials for fabrication of ladders, stairs, and railings are specified in 4ACS-640131.
6. LADDERS
6.1 Ladders, cages, safety gates, safety-closure extensions, and related equipment for most applications shall conform to the requirements as shown on 309710D, 309725D, and this standard. Ladders and railing details for LNG Heat Exchanger applications are shown on 309753D.
6.2 Ladder Technical Definitions
- Fixed ladder is a ladder permanently attached to a structure, building, or equipment, having two side rails joined at regular intervals by circular rungs on which a person steps while ascending or descending.
- Cage is an enclosure that is fastened to the ladder to encircle the climbing space of the ladder for the safety of the person climbing the ladder.
- Safety gate is a swinging self-closing device designed to eliminate or reduce the possibility of accidental falls through the ladder opening.
- Grab bars are individual handholds placed adjacent to, or as an extension above, the ladder to provide support beyond the limits of the ladder.
- Ladder safety device is any device, other than a safety gate, cage or well, designed to eliminate or reduce the possibility of accidental falls and which incorporate such features as life belts, friction brakes, and sliding attachments. Company standards do not currently implement the use of these devices.
- Well is a permanent complete enclosure encasing a ladder. Proper clearances for a well must give the person who climbs the ladder the same protection as a cage.
- Step-through ladder is one from which entrance or exit is made by stepping through the ladder to reach the landing or platform.
- Side-step ladder is one from which entrance or exit is made by stepping sideways from the ladder to reach the landing or platform.
6.3 Ladder Design Requirements in Plant
- All ladders, appurtenances, and fastenings shall be designed and constructed to meet the following load requirements, which form the design baseline of 309710D and 309725D.
- The minimum design live load shall be a single concentrated load of 200 pounds. Additional, concentrated live-load units of 200 pounds shall be considered based on the use anticipated.
- The live loads imposed by persons occupying the ladder shall be considered to be concentrated at points that will cause the maximum stress in the structural member being considered.
- The weight of the ladder, attached appurtenances, and the live load shall be considered in the design of rails and fastenings.
- Ladder support brackets (carrier support angles) indicated on 309710D and 310725D are not designed to support the entire weight of the ladder, cage, and live load without the additional support that is provided from the attachment of the ladder base. When ladder support must be exclusively from the ladder support brackets, stronger connection material might be required. Ladder support brackets for the LNG Heat Exchangers shown on 309753D are designed to allow vertical movement and have their weight support from the base of the ladder.
- Side-step ladders shall be used, wherever feasible and economical, to allow persons to step to the side rather than stepping backwards when descending from an operating platform.
- Angle-type side rails are prohibited.
- Ladders shall normally be 90 degrees from the horizontal according to Figure 1. Their use in any other position will require review and approval by Engineering Safety.
- All rungs shall have a minimum diameter of 3/4 inch. The distance between rung centers shall be 12 inches and shall be uniform throughout the length of the ladder. The odd dimensions will vary from 4 to 15 inches and shall be used for the first step from the bottom of the ladder. The bottom of the ladder shall be even with the finish grade or platform level.
- The minimum dimension between the ladder rung centerline and the face of the wall, the face of the insulation, the face of the fireproofing, or any other obstruction shall be 7 inches.
- Ladders formed by individual metal rungs that are imbedded in concrete and serve as access to pits and to other areas under floors shall have a minimum diameter of one inch and a minimum clear length of 16 inches and be so designed that the foot cannot slide off the end of the rung.
- Cages shall be provided on all ladders when the vertical distance between grade and the platform level is 12 feet or greater. The maximum vertical distance between grade and platform level shall not exceed 30 feet.
- Cages shall be provided on all elevated ladders when the distance between platform levels is 4 feet or greater. The maximum vertical distance between platform levels shall not exceed 30 feet.
- Vertical cage bars shall be continuous between the bottom hoop and top handrail when the distance from the centerline of the ladder to the edge of the platform is 3 feet or less, and/or the distance from the centerline of the rung to the edge of the platform is 4 feet.
- Two vertical cage bars, adjacent to the safety gate, shall be interrupted when access is required to an intermediate platform on a side-step ladder. Hoops shall be placed to provide 7 feet 3 inches headroom.
- Landing platforms shall be provided for each 30 feet of ladder height, or fraction thereof. Each ladder section shall be offset from adjacent sections. All landing platforms shall be equipped with standard railings and toeplates arranged to give safe access to the ladder. Platforms shall not be less than 48 inches in width from the ladder rung centerline and not less than 36 inches on each side of the ladder centerline. When a ladder cage is provided with cage bars extending to the top of the handrail, the minimum distance may be decreased to 18 inches on each side of the ladder centerline.
- Step-through ladders shall be provided with a safety-closure extension at each landing platform that will limit the step-across distance from the centerline of the rung to the nearest edge of the safety-closure extension to exactly three inches.
- Side-step ladders shall be provided with a safety-closure extension at each landing platform that will limit the step-across distance measured from the centerline of the ladder to the nearest edge of the safety-closure extension to exactly 15 inches.
- When a ladder terminates at the top of a cold box or similar structure that is equipped with standard railings, toeplate, safety gate and safety-closure extension, the enclosed area may become the intended landing platform.
- Isolated concrete pads for ladders that start at grade shall be at least 24 inches in width and 6 inches in length. The pad is intended to provide ladder support, not a landing area. Finished grade shall be within 1 inch of the top of concrete and level in the area surrounding the concrete pad.
7. STAIRS
7.1 Stairs shall conform to the requirements as shown on 309711D and 309726D and this standard.
7.2 Stairs Technical Definitions
- Stairs are a series of steps leading from one level or floor to another or leading to walking/working surfaces, landings, or platforms. A series of steps and landings having three or more risers constitute stairs or the stairway.
- Stair platform is an extended step or landing breaking a continuous run of stairs.
- Rise is the vertical distance from the top of a tread to the top of the next higher tread.
- Riser is an upright member of a step situated at the back of a lower tread and near the leading edge of the next higher tread.
- Open riser is the air space between treads of stairways without upright members.
- Nosing is that portion of tread projecting beyond the face of the riser immediately below.
- Tread is the horizontal member of a step.
- Tread depth is the horizontal distance from the front to the back of a tread including nosing.
- Tread run is the horizontal distance from the leading edge of a tread to the leading edge of an adjacent tread.
7.3 Stairs Technical Design Requirements in Plant
- All stairs and treads shall be designed and constructed to carry a load five times the normal live load anticipated, but never of less strength than is necessary to safely carry a moving concentrated load of 1000 pounds.
- The minimum width of every stairway shall be:
- 30 inches for the normal platform access/operation-type of stairway.
- 36 inches for the access/maintenance-type of stairway.
- Fixed stairs shall be installed at angles to the horizontal of between 33 and 41 degrees. See Figure 1. Any uniform combination of rise/tread dimensions may be used that will result in a stairway at an angle to the horizontal within this range. However, the rise/tread run ratios specified in Table 1 are preferred. It is highly recommended that the same angle be employed for all stairways within a facility.
- Stairs having a tread depth of less than 9 1/2 inches shall have open risers.
- No variation is permitted in the width of treads or height of risers in any flight of stairs, including any foundation structure used as one or more treads of the stairs.
- The maximum vertical distance between the finished grade and the finished upper level may not exceed 14 feet, and the vertical distance between all other landings shall not exceed 12 feet, unless an intermediate platform is provided to limit the vertical distances to these values. Stairway platforms, where required, shall be no less than the width of the stairway and a minimum of 30 inches in length measured in the direction of travel. Platforms shall be provided wherever a door or gate opens onto a stairway. The swing of the door or gate shall not reduce the effective width of the platform to less than 22 inches.
- The minimum headroom clearance shall be 7 feet 3 inches when measured vertically above landings or the leading edge of the stairway treads.
- Grating treads shall be used exclusively for all interior and exterior stairs, except where the following are used:
- Checkered plate treads shall be used only where it is mandatory to match existing conditions.
- Concrete-filled, metal pan treads shall be used only for interior stairs where the open space beneath or under the stairs would create a hazard of falling objects striking people, equipment, or machinery below.
- Each tread, intermediate landing, and the top landing of a stairway shall be constructed with nosing and the nosing shall be of slip-resistant finish.
8. RAILINGS AND OPENING GUARDS
8.1 Railings shall conform to the requirements as shown on 309712D and 309727D and this standard.
8.2 Definitions
- What is Standard railing?
- It is a vertical barrier erected along exposed sides of floor openings, wall openings, ramps, platforms, and catwalks to prevent people from falling.
- What is Stair railing
- It is a vertical barrier erected along exposed sides of stairways to prevent falls.
- What is Handrail?
- It is a single pipe supported on brackets from a wall or partition (as on a stairway or ramp) to furnish people with a handhold in case of tripping. The handrail shall be one and one-half inches in nominal diameter (two inches outside diameter). The ends of the handrail shall be turned in to the supporting wall or otherwise arranged so it does not constitute a projection hazard. All handrails shall be provided with the clearance of not less than three inches between the handrail and any other object. The height of handrails shall be 34 inches from the upper surface of the handrail to the surface of the tread in line with the face of the riser or surface of the ramp.
- What is Toeplate?
- It is a vertical barrier at floor level erected along exposed edges of areas such as floor openings, wall openings, platforms, and ramps to prevent tools and other materials from falling on people or machinery below.
- What is Platform?
- It is a surface elevated above the surrounding floor or ground for walking or working.
- What is Floor opening?
- It is an opening in any horizontal surface such as a floor, platform, or ramp, 12 inches or more in its least dimension, through which a person might fall. Examples include stair and ladder openings, pits, hatchways, and large manholes.
- What is Floor hole?
- It is an opening in any horizontal surface such as a floor, platform, or ramp, less than 12 inches but more than 1 inch in its least dimension, through which materials, but not people, might fall. Examples include belt holes and pipe openings.
- What is Wall opening?
- It is an opening in any wall or partition that has a height of at least 30 inches and a width of at least 18 inches through which a person might fall.
- What is Wall hole?
- It is an opening in any wall or partition of unrestricted width that has a height of less than 30 inches but more than 1 inch through which a person, or materials and tools, might fall.
8.3 Guarding Floor Openings and Floor Holes
- Every stairway floor opening shall be guarded by a standard railing and toeplate on all exposed sides, except at the top or bottom entrance to a stairway.
- Every ladder-way floor opening shall be guarded by a standard railing with toeplates on all exposed sides (except at the entrance to an opening) with the passage through the railing guarded with a swinging, spring-actuated, self-closing gate. Gates shall conform to details shown on 309710D and 309725D.
- Every hatchway and chute floor opening shall be guarded by either:
- A hinged, floor-opening cover and permanently attached standard railing with toeplate so only one side is exposed. When the opening is not in use, the cover shall be closed or the exposed side shall be guarded by a removable standard railing.
- A removable standard railing with toeplate on not more than two sides of the opening and permanent railing with toeplates on all other exposed sides. The removable railings shall be kept in place when the opening is not in use.
- Every pit, trapdoor, and manhole floor opening shall be guarded by a slip-resistant cover or standard manhole cover which need not be hinged in place but shall be securely held in place so that it is flush with the floor surface. When the cover is not in place, the manhole opening shall be protected along the exposed perimeter by removable standard railings.
- Every floor hole into which a person might accidentally walk/step into shall be guarded by either:
- A standard railing with toeplates on all exposed sides.
- A slip-resistant cover which is securely held in place so that it is flush with the floor surface and leaves no opening more than 2 inches wide.
- Every floor hole through which tools or materials could fall, but into which people cannot accidentally walk/step because of fixed obstructions such as equipment and piping, shall be guarded by either:
- A slip-resistant cover, which is securely held in place and is flush with the floor surface, that leaves no opening more than 1 inch wide.
- A toeplate on all exposed sides of the opening.
8.4 Guarding Wall Openings and Holes
- Every wall opening from which there is a drop of more than 4 feet shall be guarded by a standard railing. The railing may be removable but shall be hinged or mounted such that it is conveniently replaceable when access to the wall opening is necessary on a routine basis. Where there is exposure from below to falling materials, a toeplate shall also be provided.
- Every window wall opening at a stairway landing level, floor, or platform (SLFP) shall be guarded by slats, grillwork, or standard railing if there is a drop of more than 4 feet and the bottom of the opening is less than 3 feet above the SLFP. When the bottom of the opening is below the SLFP, a toeplate shall also be provided.
- Every wall hole shall be guarded with either a toeplate across the bottom of the opening or an enclosing screen of solid construction with grillwork or slat work if its lower edge is either:
- On the near side, 4 inches or less above the floor level.
- On the far side, 5 feet or more above ground, floor, platform, or stairs.
8.5 Guarding Open-Sided Floors and Platforms
- Every open-sided floor or platform that is 4 feet or more above the adjacent floor, platform, or ground level shall be guarded by a standard railing on all open sides, except where there is an entrance to a ramp, stairway, or fixed ladder. The railing shall be provided with a toeplate.
- Regardless of height, open-sided floors, platforms, or walkways above or adjacent to dangerous equipment, open tanks, and similar hazards shall be guarded with standard railings and toeplates. Where routine access is required, removable railing shall be provided.
- Dock faces at loading docks are excluded from these requirements.
8.6 Stairway Railings and Guards
- Every flight of stairs having four or more risers or rising more than 30 inches, whichever is less, shall be provided with stair railings.
- Stairways that have both sides enclosed and a width of less than 44 inches shall have at least one handrail, preferably located on the right descending side.
- Stairways that have one open side and a width of less than 44 inches shall be provided with a stair rail on the open side.
- Stairways that have both sides open and a width of less than 44 inches shall be provided with one stair rail on each side.
- Stairways 44 inches wide or more, but less than 88 inches, shall be provided with a handrail on each enclosed side and one stair railing on each open side.
- Stairways 88 inches or more in width shall be provided with one handrail on each enclosed side, one stair railing on each open side, and one intermediate-stair railing located approximately midway of the width.
8.7 Railing and Guards Design Requirements
- All handrails and railings shall be designed and constructed to meet the following load requirements, which form the design baseline of 309712D and 309727D.
- Anchoring of posts and members for railings shall be of such construction that the completed structure will be capable of withstanding a load of at least 200 pounds applied in any direction except upward. Load on rails shall be applied at the mid-point without exceeding maximum allowable deflection discussed in ASSE A1264.1.
- Wall opening screens shall be of solid construction, of grill work having openings of not more than 4 inches in any direction, or of slat work having openings not more than 2 inches in width and unrestricted length and shall be capable of withstanding a load of at least 200 pounds applied horizontally at any point on the near side of the screen.
- Coverings located on a floor such as floor opening covers, manhole covers, and their supports shall be designed to take a live load at least as great as that for which the adjacent floor is designed.
- Angle railings shall be used exclusively where railings are required, including all stairs, platforms, guardrails, and catwalks. Pipe railing shall be used only where it is necessary to match existing conditions.
- All handrails and railings shall be provided with a clearance of not less than three inches between the handrail or railing and any other object.
Figure 1 – Pitch Range for Fixed Ladders, Stairs, and Inclines
Table 1 – Permissible Range of Rise/Tread Run Ratio
Figure 2 – Application for Fixed Ladders
