by Wayne Maynard
Slips, trips and falls in outdoor environments can be caused by rain, sleet, ice and snow and particulate soil that cause surfaces to become slippery or produce poor traction.
While we cannot control environmental conditions that increase slipperiness of outdoor walkway surfaces, we can certainly reduce the likelihood of falls through improved design of exterior sidewalks, curbs, parking areas, improved lighting and improved maintenance to increase awareness and eliminate hazards.
Reducing Trip Hazards
A trip occurs when the foot strikes a near-ground obstacle that abruptly arrests the movement of the foot when the body's center of gravity is in motion. This causes the center of gravity to rapidly move out of the area of the body's support base (the planted foot), resulting in a fall.
A trip most often results in the person falling forward, while a slip most often results in the person falling backward.
Most state, local and federal codes and standards describe changes in level of 1/4 inch or higher in the course of travel as a trip hazard. These obstacles should be eliminated through facility design or maintenance, if at all possible. However, if elimination is not possible, other options include:
- For changes in level of 1/4 inch to 1/2 inch (6 mm to 13 mm), bevel the edge with a slope no greater than 1:2. The slope is the angle of incline, usually given as a ratio of the rise (or vertical height) to the run (or horizontal length). The larger the run, the more gentle the incline angle.
- For level changes greater than 1/2 inch (13 mm), install a ramp with a maximum slope of 1:12.
- A third, but less desirable option, is to make the hazard noticeable through appropriate detectable warnings.
Preventing Slips and Falls
A business owner may not be responsible for injuries resulting from a fall on a public sidewalk located outside his or her property.
However, some courts may impose liability for injuries on a sidewalk used exclusively by customers coming to and from the business. (Consult with your legal counsel if you have questions on liability.)
A parking lot owner, however, can be responsible for maintaining the parking lot in a manner such that it is reasonably safe for people using it. This includes:
- Filling and patching cracks and holes.
- Repairing and eliminating raised areas due to tree roots, settling, cold weather (frost heaves) and ordinary wear-and-tear.
- Reducing surface water by directing roof drainage away from sidewalks and parking areas.
- Clearing sidewalks/parking areas of snow/ice before employees and guests arrive.
- Centering and securing parking stoppers.
- Painting or staining parking stoppers near entrances "safety yellow" to improve visibility.
Curb Ramps and Handicap Ramps - State, local and national codes specify guidelines/requirements for curb ramps and handicap ramp design. For example, ramp slopes of 1:15 minimum to 1:12 maximum with "slip-resistant" surfaces often are cited.
There are no specific guidelines as to what "slip-resistant" means, but some codes specify grooving or other alterations of the curb ramp to improve slip resistance.
Check with your state and local codes for requirements on ramp slip-resistance guidelines. Handicap ramps and curbs should be colored "safety yellow." (See the section on Color, Contrast and Visible Warnings.)
Entrances - For outdoor walkways at entrances exposed to the elements, consider installing a canopy to reduce snow, ice and water from being tracked into the building.
Color, Contrast and Visible Warnings - Recent U.S. Access Board Research recommends "safety yellow" as the preferred color for persons having very low vision. Yellow or yellow-orange warning surfaces are preferred over black warning surfaces. "Safety yellow," therefore, is a color standardized for use as a warning in the pedestrian/highway environment.
Lighting - Inadequate lighting also may lead to accidents involving falls in parking lots, trips over curbing, falls on a step or stairs from a parking lot to a store and trips and falls due to holes, cracks and uneven surfaces.
Recommended outdoor lighting levels for general parking, ramps and corners, pedestrian areas and entrances are given in LP 628, Lighting for Safety and Performance.
Once physical hazards such as uneven pavement, poor lighting and unmarked ramps are remedied, then attention can be turned to the weather-related conditions of walking surfaces.
Slips and falls from snow, rain and ice are common in northern climates. Falls can be caused by inadvertent accumulation of ice and snow due to misapplication of deicing measures. Misapplication can be caused by selecting less-efficient de-icing chemical(s) and friction additives (sand), and inadequately managing application schedules.
Effective ice removal often occurs during the day with full sun. But full sun will melt adjacent snow or ice, placing water on the de-iced walking surface. This will dilute the solution and tend to refreeze at night. With dropping temperatures, ice can re-form with falls occurring first thing in the morning.
The initial step in de-icing is choosing a de-icing agent. When selecting ice-melting chemicals, here are some things to remember:
- Rock salt (sodium chloride) is the least expensive but is somewhat corrosive and can damage concrete, interior surfaces and vegetation. It may need a wetting agent when used at low temperatures.
- Calcium chloride and magnesium chloride are more effective than rock salt, and most effective at lower temperatures. Magnesium chloride is somewhat less corrosive than calcium chloride, which is about as corrosive as rock salt.
- Calcium magnesium acetate is the most environmentally friendly but is more expensive and is least effective at lower temperatures.
Sidebar: Tips For Managing Slips and Falls
The Iowa Transportation Center at Iowa State University offers these guidelines for managing slips and falls from snow, ice and water:
- Plow, shovel and use de-icing, salting or ice melting chemicals to remove ice and snow.
- Pre-apply de-icing chemicals before a storm, followed by snow/ice removal during and after the storm. Use plenty of de-icing materials, as using "barely enough" will leave patches of ice.
- Check the surface regularly. For parking areas, this can be time-consuming, but it is well-worth the effort.
- Aim for evaporation. If the water can drain (e.g., drains aren't blocked) and there is full sun or even reasonable wind, the water (even ice) will evaporate. A dry pavement is a clear indication there is no ice.
- Use a friction additive. Sand is the most popular because it's cheap. Use a lot of it. Make certain that anyone walking on the surface has a lot of traction. You can clean up the mess once the bad weather is over.
- Check and treat surfaces every morning, especially around snow piles where melting may have created new problem areas. Reevaluate during the day and re-treat as needed.
- Remember that a clean-looking surface is only "safe" if it is dry. A wet surface can contain ice and also can turn to ice in the shade or overnight.
- Hold facility managers, custodians, grounds maintenance staff and contracted snow removal personnel responsible for snow and ice removal.
- Train those responsible in procedures for safely maintaining walkway surfaces, including the location of equipment and supplies.
Source: Technology News, August 1995, Iowa Transportation Center, Iowa State University.
U.S. Access Board: Americans with Disabilities Act (ADA) Accessibility Guidelines for Buildings and Facilities. July 2004.
U.S. Access Board: Technical Bulletin: Ground and Floor Surfaces.
ASTM F1637, Standard Practice for Safe Walking Surfaces, ASTM International, West Conshohoken, Pa.
ANSI/ASSE A1264.2 -2006, Provision of Slip-Resistance of Walking/Working Surfaces.
Maynard, W.S., Chang, W.R., and Curry, D.G., Industrial Flooring, Health and Safety International. 2004.
American National Standards Institute (ANSI) Z535.1 - 2002, Safety Color Code.
International Organization for Standardization (ISO) 3864-2004, Safety Colours and Safety Signs.
(Author's Note: The illustrations, instructions and principles contained in the material are general in scope and, to the best of our knowledge, current at the time of publication. No attempt has been made to interpret any referenced codes, standards or regulations. Please refer to the appropriate code-, standard- or regulation-making authority for interpretation or clarification.)
Wayne Maynard is product director of ergonomics and tribology at the Liberty Mutual Research Institute for Safety in Boston.