A Longitudinal Study of Playground Surfaces to Evaluate Accessibility - Final Report

Engineered Wood Fiber

There were six sites surfaced entirely with engineered wood fiber (EWF).  In addition, there were five sites surfaced with a combination PIP and EWF, and eight sites surfaced with a combination TIL and EWF.  The EWF ranged in cost from $ .74/sq. ft. to $2.50/sq. ft.  One of the emerging playground surfacing trends is to install a unitary surface, such as PIP or TIL, as the primary accessible route to accessible equipment and fill the remainder of the equipment use zones with a less costly loose fill surface material, EWF or shredded rubber (SHR). While this has been thought to be a cost effective solution to playground surfacing, the loose fill material has caused more maintenance issues when combined with a unitary surface.

The playground sites in the sample with EWF experienced the greatest frequency of high SDS and mean for firmness and stability.  Every playground installed with EWF was observed with undulation across the horizon of the surface area.  The undulating surface material created changes in level, running and cross slopes exceeding the maximum allowable standards resulting in non-compliant accessible routes to play components.  There was no observational difference in the issue of undulating surface between sites installed by maintenance personnel compared to sites installed by contractors.  Review of installation data and discussions with staff indicated the loose fill surface installations did not follow the same procedures noted in the installation instruction by the surface manufacturer or in ASTM F1951‒99 lab reports.  EWF surface installations were mostly infilled, raked and leveled.  A minimum amount of surface compaction was conducted, if any.  This is a serious departure from the installation procedure used on the lab test samples for ASTM F1951‒99, where the surface material is installed in 3‒6 inch layers, watered, raked, compacted and installed with another layer following the same procedure and finally compacted with either a drum roller or mechanical tamper. 

Some EWF marketing literature reports that the surface material will naturally settle and compact over time and with visitor use.  Observations at new installations with heavy visitor use indicate the high traffic may actually create even greater peaks and valleys in the undulating surface.  At the sites where the surface material has had the opportunity to naturally settle, several occurrences were noted where there were changes in level greater than .50 inches at the point of entry to the playground from the sidewalk or at transitions with unitary surfaces. 

Large areas where the loose material had been displaced under heavy use areas with motion such as at swings, slides, sliding poles, climbers, spinners, and teeter totters were observed at all of the sample sites with EWF.  A kick-out area at a swing could be as large as 3 ft. x 8 ft. with a depth of more than 5 inches.  The accessibility standards require the minimum 30 x 48 inch clear floor space for transfer to/from the accessible play components have a level surface with less than a 2.08 percent cross slope in all directions.  The displaced surface material at locations such as the bottom of slides, a swing, or ground level play component rendered the accessible route to the play component non-compliant with the accessibility standards. Maintenance issues at sites began to emerge where the product was filled at the kick-out area rather than the raked level, compacted and then filled and compacted.  Where the kick-out areas had been filled, again it would eventually be displaced.  This time it created higher undulating mounds at the front and back of the kick-out area and greater cross slopes within the required clear floor space. 

At locations where the EWF was paired with a unitary surface, deficiencies were identified at the transition between the two surface materials.  The EWF had settled by 1‒5 inches creating a change in level of excessive running slope up to 16 percent at the transition.  This was most prevalent at sites installed with PIP as the primary access route. At locations where TIL was intended as the primary accessible route and EWF was used as secondary safety surfacing, the EWF particles began contaminating the TIL seams.

To the layman, the terms EWF and woodchips are often, incorrectly, interchanged.  The difference between EWF and wood chips is one where the EWF goes through several additional processes following the output from what would come from a typical landscape chipper.  Unlike woodchips out of the chipping equipment, EWF is then shredded again, stamped/flattened and made pliable to the extent that the particles will weave together to create a traversable, impact attenuating surface.  In addition, there is an ASTM standard specification for EWF, further distancing the material from any product made on site or purchased from a nursery or home improvement store.  The ASTM standard for EWF requires the particles be small enough to pass through a series of three sieves, ¾ inch, 3/8 inch and No. 16 (0.0469 inch).  The sample is considered compliant if there is no more than 1 percent residue is left on any individual sieve.  Large wood particle chips, chunks and shredded twigs were found at all of the EWF sample sites.  The observable quantity of large wood particles raised into question whether a test sample from any of the sites would comply with the ASTM standard specification for EWF and specifically the sieve test.  In addition to the large particles, there were instances where vegetation and mold were found growing in the surface material.

A conference call was conducted with all of the playground owners prior to the release of the first year finding report in 2011.  At this time, acquisition, installation and maintenance of EWF was thoroughly discussed.  Owners cited the ability to buy directly from mills with ASTM-IPEMA lab certificates as a process to purchase the product at lesser cost than buying directly from the manufacturer. They also stated that no installation instructions accompanied the surfaces from the manufacturer or the mill,.  Thus, none of the owners were aware of any need to install the surface materials in layers by watering and compaction. 

Sites visited in 2012 showed a marked improvement in SDS where playground owners participated in the conference call and gained greater information on the compaction requirement for installation and maintenance.  One site utilizing PIP as the primary access route and EWF as the secondary access route was assessed with less than 1 percent slope at the transition between the two surface materials.