Catching kids when they fall: guidelines to choosing a playground surface.

The importance of proper resilient surfacing in playground safety has become widely recognized in recent years. Indeed, since the US Consumer Product Safety Commission (CPSC) has estimated that up to 60% of playground injuries may be caused by falls to the surface, and since injuries from falls to the surface tend to be among the most serious playground injuries, it can be argued that providing a shockabsorbing surface under playground equipment may be the single most important action that can be taken to improve a playground's safety. While the decision to provide resilient playground surfacing is fairly straight-forward, the choice of which surface to use is much more complex. There are literally dozens of playground surfaces available to the playground administrator today. Furthermore, in addition to shock absorbency, many other factors--such as accessibility, maintenance and cost--must be considered. This article will survey the most commonly used playground surfaces and their performance in the key areas of shock absorbency, accessibility, cost, and maintenance.

Types of Resilient Surfacing

Resilient playground surfaces commonly used in the United States include inorganic loose fill materials (sand and gravel) organic loose fill materials, wood mulch, bark mulch and wood chips, wood fiber, rubber mats, and troweled-in-place rubber surfacing. All of these categories will be discussed in this article.

Other, less frequently used surfaces include rubber particles or shredded rubber; closed cell foam overlaid with rubber sheeting; and rubber foam or mats topped with artificial turf or indoor/ outdoor carpet. These systems, however, will not be discussed in this article.

Shock Absorbency

Shock absorbency is the most critical consideration in choosing a playground surface. Surfacing that does not offer adequate shock absorbency should not be used under playground equipment no matter what other advantages it may offer.

In order to provide a means of assessing s hock absorbency, the American Society for Testing and Materials (ASTM) has specified a test procedure to measure the deceleration imparted to an instrumented headform when it strikes a sample of surfacing material. ASTM and the CPSC recommend that the peak deceleration at impact not exceed 200 times the acceleration due to gravity (200 Gmax) and that HIC (Head Injury Criteria) be less than 1000, a measure of deceleration over the time which the headform decelerates to a halt. According to the CPSC, if these two measures are met, a life-threatening head injury would not be expected to occur.

The critical height of a material, a term used by the CPSC and others, is the maximum height at which the peak deceleration is less than 200 Gmax and HIC is less than 1000. The CPSC recommends that resilient surfacing around a piece of playground equipment have a critical height equal to or greater than that of the highest accessible part of the equipment.

This recommendation rules out the use of asphalt and concrete, which exceed 200 Gmax at a critical height of only two inches. Soil, hard-packed dirt, grass, and turf are also not recommended because their shock absorbency may be poor due to wear, moisture absorption, and packing.

Suppliers of the most common loose fill materials rarely provide shock absorbency test data, since these materials are most commonly used for construction or landscaping purposes, not playground surfacing. Therefore the CPSC tested several widely used materials for shock absorbency and published the results in The Handbook for Public Playground Safety (see Fig 1).

FIGURE 1. CRITICAL HEIGHTS (IN FEET) OF COMMON LOOSE MATERIALS

                              Uncompressed Depth   Compressed Depth

Material                     6 inch   9 inch   12 inch   9 inch

Wood Mulch                      7       10        11       10

Double Shredded Bark Mulch      6       10        11        7

Uniform Wood Chips              6        7       >12        6

Fine Sand                       5        5         9        5

Coarse Sand                     5        5         6        4

Fine Gravel                     6        7        10        6

Medium Gravel                   5        5         6        5

Source: The Handbook For Public Playground Safety, US Consumer Product Safety Commission

A depth of six to 12 inches of most of these materials provides critical heights of five to 10 feet. This range covers the highest accessible part of most playground equipment sold in the US today. Loose fill materials lose some shock absorbency under compression, which is likely to occur on most playgrounds from user foot traffic.

While the critical height information is extremely useful, some questions about the shock absorbency of loose fill materials remain unanswered. The published CPSC tests were conducted at ambient temperatures, and thus provide no information about performance at high and low temperatures. Additionally, users of loose fill materials must ensure that the materials that they use are similar in composition to those tested by the CPSC to be certain of equivalent shock absorbency. Finally, some other possible loose fill materials like bark nuggets, shredded rubber and ground rubber have not been tested.

Some of these questions may be answered by The National Program for Playground Safety at the University of Northern Iowa, which is being funded by the Centers for Disease Control and Prevention (CDC) of the United States Public Health Service (See Hudson, Thompson and Mack, p.69). This program includes research on the performance of most common types of playground surfaces, according to ASTM 1292, which requires testing at 120 [degrees] F and 30 [degrees] F in addition to testing at ambient temperatures. The results of the this program may provide information about a wider variety of resilient surfaces at varied temperatures. Results of this testing are expected to be available later this year. More information on this testing, and other aspects of the National Program for Playground Safety, may be obtained by calling 800-554-7529.

The most popular commercially available resilient playground surfaces include wood fiber, which consists of elongated hardwood fibers, usually sold with an underlying drainage system; rubber mats made from recycled rubber particles bonded together with an adhesive; rubber mats compression molded using vulcanized virgin or recycled rubber; and troweled-in-place rubber systems made up of rubber particles bound with an adhesive, usually consisting of a recycled rubber base coat and a colored virgin rubber top coat (see Fig 2).

FIGURE 2. CRITICAL TYPICAL HEIGHT RANGES (IN FEET) OF COMMON COMMERCIALLY AVAILABLE PLAYGROUND SURFACING

Material                           Thickness   Critical Height

Wood Fiber                             8"            10'

Bonded Rubber Tile                   1-1/2"           4'
                                     3-9/16"         10'

Vulcanized Rubber Tile               1-3/4"           6'
                                     4-3/4"          12'

Troweled in Place Rubber Surface       2"             5'
                                       5"            11'


Based on ASTM 1292-93 (less than 200 Gmax and 1000 HIC at 30[degrees],
70 [degrees] and 120 [degrees] F) test results.

Source: Survey of surfacing suppliers

Users of these systems must obtain information on shock absorbency from the supplier. Suppliers should be able to provide results from an independent testing laboratory that verifies the critical height of their surfacing material, allowing the user to know for certain the shock absorbency of the playground surface that is being used.

Accessibility

The federal government's regulations and guidelines affect a second aspect of playground surfacing. The Americans with Disabilities Act, which broadly prohibits discrimination on the basis of disability, became effective for public and private providers of recreation, leisure and entertainment in January, 1992. Thus playground operators must now ensure that their playgrounds are accessible to the disabled.

The Access Board, the US federal agency responsible for accessibility design is currently developing guidelines for recreation facilities. Additionally, in December, 1996, ASTM adopted a provisional standard, PS 83, for playground surface accessibility testing. The Access Board is expected to lean heavily on the ASTM standard, which specifies tests for playground surface maneuverability and surface regularity, in developing accessibility guidelines for playground surfacing.

Maneuverability is a measurement of the effort to move a wheelchair across a surface. The standard contains tests of effort for both straight ahead and turning movement, using a force wheel on a rehab wheelchair as the measuring device. In order to pass the test, the force required must be less than that required to propel the chair up a ramp with a one in 14 slope.

Surface regularity addresses surface evenness, which reduces the possibility of crutch tip, walker or caster wheel entrapments and minimizes excess rolling effort required by surface cavities. The standard requires that there be no surface cavities large enough to accommodate a cylindrical probe three inches in diameter and two inches deep.

The revised standard is expected to be published during the first half of 1997, with testing by many playground surfacing suppliers likely to follow shortly thereafter.

In addition to the ASTM provisional standard for accessibility there are several other aspects of playground surfacing accessibility that are of interest.

First, at least a portion of the surface that provides a path to the playground equipment must be accessible. If a disabled user (or a disabled parent or guardian) cannot reach the playground equipment, then the playground is not accessible. Ideally, the entire playground surface should be accessible.

Secondly, common loose fill materials --both organic and inorganic--are considered inaccessible. Experiments by Beneficial Design, Inc., an accessibility testing and consulting firm, have shown that sand and pea gravel require three to six times as much force to move a loaded wheelchair across their surface than a three-quarter-inch level pile carpet with padding, which in itself is often considered inaccessible. Additionally, the City of Green Bay, (WI), agreed to remove wood chips from one of its playgrounds based on an advisory from the Department of the Interior. The advisory was in response to a complaint issued by the family of a disabled individual who was unable to use the playground.

The Department of the Interior (DOI), in its advisory to the City of Green Bay, ruled that both wood fiber and rubber matting may be accessible under certain conditions, however, concerns were expressed about both materials. DOI indicated that while the elongated wood pieces that make up wood fiber may knit together to form an accessible surface, the time period for this to take place, (30 days or more) may require additional installation steps. Other concerns expressed about wood fiber included displacement due to user activity; looseness due to moisture; and settling of the wood fiber which may put equipment transfer points above the required height for users in wheelchairs. Thus proper installation, adequate drainage and regular maintenance and replenishment of displaced material are required to maintain wood fiber as an accessible surface.

DOI advised that rubber matting materials are accessible almost immediately after installation. Regular inspection to ensure the integrity of the surface and adequate drainage were recommended.

Based on the Green Bay decision, the most common commercially available playground surfaces -- wood fiber, rubber matting and troweled-in-place rubber surfacing -- may be accessible under certain conditions. Other commercially available materials (e.g. closed cell form or mats topped with rubber sheeting or carpet) may also be accessible.

When evaluating commercially available accessible playground surfaces, users should request the results of testing according to the ASTM standard; installation required to achieve accessibility; and maintenance required to provide continued access.

Initial Cost

The initial cost of resilient playground surfacing depends not only on the cost of the surfacing material itself but also upon site preparation and installation costs.

For example, natural loose fill materials--both organic and inorganic--require a base of drainage stone covered with a porous sheet material to provide adequate drainage, and a containment barrier to hold the loose resilient material in place.

In this case, the cost of materials and labor for site preparation and containment usually exceeds the cost of the resilient material. While organic loose fill materials are usually more costly than inorganic loose fill, when site preparation and containment costs, which are roughly the same for both types of material, are added, the difference in total installed cost can be minor.

Wood fiber systems also require drainage and containment. In many cases this is accomplished with proprietary materials provided by the supplier as part of the system. Additionally, some suppliers provide synthetic mats or pads for high-wear areas. Finally, the cost of the wood fiber material itself is usually higher than common organic or inorganic loose fill materials.

For all of these reasons, wood fiber systems tend to be more expensive than common loose fill resilient surfaces.

Site preparation and installation are also important factors in the cost of rubber resilient surfacing materials. If the existing playground surface is asphalt or concrete, site preparation costs are usually minimal, limited to cleaning the surface (the surface should also have good integrity and be adequately sloped for drainage). Rubber tile or troweled-in-place rubber can then be installed directly over the hard surface. Rubber surfacing is often used in these instances to avoid the costs and difficulty of excavating asphalt or concrete and providing adequate drainage.

If a hard base is not available, a substrate of concrete, asphalt or compacted stone must be installed for rubber surfaces. Rubber tiles are then glued or mechanically fastened to the substrate or to adjacent tile. In the case of troweled-in-place rubber systems, a base coat of recycled rubber and binder is installed directly onto the substrate. After the base coat cures, a virgin rubber wear layer is installed over the base coat. Troweled-in-place systems are almost always installed by specialized contractors with training and experience with this type of system.

Material and installation costs for rubber playground surfacing exceed those of wood fiber or common loose fill materials, as do site preparation costs, unless the existing surface is concrete or asphalt. Troweled-in-place rubber surfaces are usually more expensive than rubber tile because of the materials used in the wear coat and the high, specialized labor content.

The relative initial costs of the most common resilient playground surfaces are shown in Fig. 3.

[Figure 3 ILLUSTRATION OMITTED]

Maintenance

Maintenance of playground surfacing --including inspection and renewal--is critical to the performance of the surface. A surface that is not properly maintained can rapidly be worn or kicked away, negating its shock-absorbing properties. Broken glass, trash or animal excrement in or on the surface can present additional hazards (see Fig. 4).

FIGURE 4: SURFACING INSPECTION, MAINTENANCE AND REPLACEMENT PROCEDURES

Check for:

Inspection

[] broken glass, trash, animal excretion, rocks and other dangerous materials

[] adequate surface thickness to maintain required shock absorbency

[] hard, compacted surface; frozen surface; damp compacted surface; standing water; exposed hard surface like footings

[] trip hazards (exposed footings, raised tile edges, rocks, loose fill, retaining walls not clearly visible)

Routine Maintenance

[] rake, level loose fill or wood fiber materials to proper depth to maintain required shock absorbency and to maintain wheelchair to equipment transfer distances for accessible surfaces

Renewal/Replacement

[] replace compacted or deteriorated fill materials

[] top off loose fill materials to maintain required depth

[] replace or repair damaged rubber surfaces

The proper frequency of inspection and maintenance is critical. Although it will likely prove to be the most costly aspect of playground surfacing, inspection must occur often enough to maintain a safe and effective surface. Frequency of maintenance and inspection is also greatly influenced by playground use levels, environment (e.g. vandalism, contamination), and type of material. See Fig. 5 for frequency of inspection, raking and leveling, and renewal for common types of playground surfaces as recommended by playground safety consultants and playground administrators.

FIGURE 5. TYPICAL MAINTENANCE FREQUENCIES

               Inorganic Loose      Organic Loose Fill   Wood
               Fill (Sand/Gravel)   (Mulch/Wood/Chips)   Fiber

Inspection     Daily - Weekly       Daily - Weekly       Daily -
                                                         Weekly

Rake & Level   Daily - Weekly       Daily - Weekly       Weekly -
                                                         as
                                                         required

Replace        Not required         Mulch - Yearly       Usually
               (unless              Hardwood -           not
               compacted            Usually              required
                                    not required

Top Off        1 - 3 years          1 - 3 years          3 years
                                                         (more
                                                         frequently
                                                         in high
                                                         use
                                                         playground)

               Rubber Matting       Troweled-in-
                                    Place Rubber

Inspection     Weekly               Weekly

Rake & Level   Not required         Not required

Replace        Replace damaged      Repair as required
               tiles as required

Top Off        Not required         Not required

Note: This table shows typical maintenance frequencies. Users should determine frequencies for their own playground based on use levels and operating environment.

Figs. 6 and 7 show estimated surfacing maintenance costs for two park districts in mid-size cities in the Midwest and east, one with an organic loose fill surface and the other with rubber tile surfacing.

FIGURE 6. NATURAL ORGANIC SURFACING MAINTENANCE COSTS MIDWESTERN PARK DISTRICT PLAYGROUND

Description: Play equipment includes one composite structure, an adult to-fro swing set, a toddler swing set, and three spring animals. Surface is wood chips, 12 in. deep, 5,000 sq. ft. area.

Inspection: Time Required x Frequency x Cost/Hr. = Annual Cost

Inspection 22 minutes 3 times/week Transit 30 minutes

52 minutes

.87 hours x 156/year x $14.50/hour = $1,968

(Note: Additional time may be required to remove debris found in loose fill.)

Rake and Level: Time Required x Frequency x Cost/Hr. = Annual Cost

22 minutes Weekly .37 hours x 52/year x $14.50 = $279

Top Off: Time required x Frequency x Cost/Hr. = Annual Cost

2.5 x 1 year x $14.50 = $36

Material Quantity x Cost/Cu.Yd. = Annual Cost

55 cu. yds. x $12/cu.yd. = $660

Total Annual Cost = $2,948

FIGURE 7. RUBBER SURFACING MAINTENANCE COSTS EASTERN PARK DISTRICT PLAYGROUND

Description: Play equipment includes a small composite structure, an adult to-fro swing set, a toddler swing set, a whirl, and two see-saws. Surface is rubber tile, 2 1/4" and 3 1/4" thick, 2,600 sq. ft. area.

Inspection: Time Required x Frequency x Cost/Hr. = Annual Cost

Inspection 15 minutes 1/wk.

Transit 30 minutes

Total 45 minutes

.75 hours x 52/yr. x $16/hr. = $624

(Note: Additional time may be required to remove debris found on rubber surface.)

Replace or Repair Rubber Surface

None required to date. First site installed in 1993, balance in 1994 and 1995.

Total Annual Cost = $624

Summary and Conclusions

The preceding discussion has shown that there is no ideal resilient playground surface. Each type of surface has advantages in some performance or cost areas and shortcomings in other areas (see Fig. 8).

FIGURE 8. PERFORMANCE OF RESILIENT PLAYGROUND SURFACES

Inorganic Loose Organic Loose

(Sand, Gravel) (Mulch, wood Chips) Wood

Fiber

+ indicates superior category

0 indicates average in this category

- indicates below average in this category

na not acceptable

Rubber Mats

Troweled-in-Place

Shock Absorbency 0

Accessibility +

Low Initial Cost -

Frequency of + Maintenance/Renewal Required

A facility with high playground use levels, frequent vandalism and littering, and a limited maintenance budget, may find rubber matting the best playground surface. A different facility with lower use levels, and where maintenance personnel are on site daily for trash pick up or other duties, may find low cost organic and inorganic loose fill materials a wise choice.

In all cases some part of the playground or playground complex should be covered with an accessible surface and all playground surfaces should provide adequate shock absorbency for the equipment on the playground. Unfortunately, many playground surfaces in the US do not meet these requirements for safety and accessibility. The challenge for those with an interest in playgrounds and playground safety is to work to make all playground surfaces safer and more accessible to all.