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

Performance for Surface Firmness and Stability

In addition to the visual inspection and calculation of the surface deficiency score, the firmness and stability of the surfaces were measured at each of the nine locations using the Rotational Penetrometer (RP).  Research with the RP shows repeatability and reproducibility consistent to that of the test procedure for ASTM F1951‒99 which utilizes a wheelchair work method.  Similar to the F1951‒99 lab test, smaller values would indicate less work force necessary to move across the surface, while higher values would indicate greater work force to move across the surface.  Prior to taking readings of the playground surfaces, baselines were established on cement or asphalt. The baseline for firmness ranged from .14 to .16 inches and the baseline for stability ranged from .16 to .18 inches. The baseline measurements affirmed the RP was operable and calibrated. Using the RP at each location, five readings were taken and then averaged to result in one measurement for said location.  Thus, in a playground identified with all nine locations, a total of 45 readings were collected, five at each location.

Table 5 shows the measurement mean for firmness and stability by surface type.  Interestingly, all four of the surface types have a mean less than .50 inches for firmness.  The second reading, for stability, begins to illustrate the difference among surface types.  The mean for stability remains under .50 inches for the three types of unitary surfaces, while the loose fill, EWF, has a mean for stability of .78 inches.

Table 5
Firmness and Stability by Surface Type

(N) = Number of locations visually inspected.

The stability measurement, the second measurement in the series using the RP, showed a wide range of results among the different surface types.  The stability measurement had a minimal range of .04 to .06 inches for the unitary surfaces, while the loose fill EWF had a difference of .44 inches.  Also of note was that the standard deviation for stability with the EWF was the highest at .13, double that of any other surface type.  The high standard deviation for EWF raises questions whether the material characteristic for stability and its high variability can serve as a preliminary indicator that surface types with greater variance will require additional maintenance over time.  Interestingly, the two surfaces that are most characteristically different from one another, PIP and EWF, do not have statistically different values for firmness in this study sample.  As noted in Table 5, their mean for firmness is essentially the same. 

Over the course of the study, members of the study advisory committee suggested that the sum of the firmness and stability measurements should be considered as a starting point to develop a pass/fail value for the field test with the RP.  Table 6 shows the mean score for the measurements of firmness and stability when added together along with the range of high and low measurements.  The TIL has the lowest Mean = .58 inches when the average measurements of firmness and stability are added together.  As one might predict, EWF has the highest Mean = 1.12 inches for the sum of firmness and stability.