Frequently Asked Questions on the Development of a Field Test Method for Measuring the Firmness and Stability of Surface Systems

Prepared by the National Center on Accessibility
June 2010

In 2005, a task group within the American Society of Testing and Materials (ASTM) F08.63 Subcommittee on Playground Surfaces began working on the development of a test method to objectively measure firmness and stability of surfaces systems as related to accessible routes on playgrounds. This test method can be used  by playground owners, facility managers and others  as a method for measuring firmness and stability of surfaces. The following FAQ’s have been prepared by the National Center on Accessibility to provide background  information to playground owners, recreation practitioners, and others  about the field test method for measuring surface firmness and stability.

1.       What is the “rotational penetrometer”?

Illustration of rotational penetrometer.The rotational penetrometer is a portable field test designed to measure surface firmness and stability. The rotational penetrometer consist of two identical, symmetrical surface reference plates, a frame, and a penetrator assembly incorporating a wheel or caster assembly and a means of applying a load to the penetrator. The two surface reference plates contact the surface and distribute the weight of the operator. The penetrator rotates about a vertical axis relative to the surface reference plates allowing for measurement of firmness and stability of the surface. Two types of measurements are taken with the device. The first measures the initial penetration into the surface, the firmness reading. From that point, the wheel or caster is moved back and forth four times and device gives the second measure of displacement into the surface for stability.

2.    Why a test method for surface “firmness” and “stability”?

Accessibility standards such as the Americans with Disabilities Act Accessibility Guidelines (ADAAG, 1991, revised 1994), the Uniform Federal Accessibility Standards (1984) and the Architectural Barriers Act Accessibility Standards (ABAAS, update effective 2006) include a technical provision that requires the surface of accessible routes, clear spaces, and turning spaces serving people with disabilities be “firm and stable.” This language dates back to the 1960s and A117.1 Accessible and Usable Buildings and Facilities, the first nationally recognized technical provisions addressing accessibility in public spaces, developed by the American National Standards Institute (ANSI). A definitive performance measure provides information about the level of surface “firmness and stability.”

3. What other tests have been used to measure surface “firmness and stability”?

A laboratory test using the “wheelchair work method” was developed in 1999 to measure playground surfaces. This is standard is known as ASTM F1951-99 Standard Specification for Determination of Accessibility of Surface Systems Under and Around Playground Equipment, the first attempt to provide more objective criteria for measuring “firmness and stability” of surface materials. ASTM F1951-99 measures the work required to traverse a surface during a straight propulsion in wheelchair and during a 90 degree turn.

ASTM F1951-99 laboratory test method.
ASTM F1951 straight propulsion test. ASTM F1951-99 turning test.
Straight propulsion test. 90 degree turn test.

4. How would surface “firmness and stability” be determined if a complaint is filed under the ADA or the ABA?

Without a referenced test method, “what” constitutes “firm and stable,” will continue to be determined by the courts, individual investigators from federal offices of civil rights, and through private rights of action where settlement agreements have negotiated corrective actions to make surfaces on accessible routes more usable for people with disabilities. Through subjective inspection, summary judgment or settlement, woodchip (City of Green Bay Parks and Recreation Department, 1993; San Francisco Unified School District, 1995; Mt Diablo Unified School District, 1998-2007;), pea gravel (U.S. Department of Interior National Park Service Office of Civil Rights, 1999), sand (City of Weston, 2008) and other outdoor surface materials have been found to be not firm or stable for use on the accessible route. No quantifiable data on the firmness and stability characteristics of these surfaces exists. Without a field test method to objectively determine the firmness and stability of various surface materials, the accessibility of every surface material will be left to the courts to decide.

5. Why use the “rotational penetrometer” to conduct field tests on playground surfaces?
Rotational penetrometer in use for field test.A field test is needed to verify the firmness and stability of the surface over time and under various conditions of use.  A surface that is not maintained over time can degrade in performance. A surface installed and tested in the laboratory setting may have different characteristics than when it is installed in the field, which can produce different firmness and stability results. For example, a surface material may be tested at an indoor laboratory with a sample originating from a plant in California, but then installed at a site with material distributed by an Ohio plant. In another example, the surface material may have very good laboratory results based on the manufacturer installation instructions, but on site the installation of the surface material deviates from the manufacturer instructions. A field test for firmness and stability on site enables a manufacturer or playground owner to measure the surface material and judge whether additional material, compaction or maintenance may be required to achieve optimum access for people with mobility impairments.
6. Are the results of the rotational penetrometer “repeatable and reliable”?
A recent interlaboratory test using six different rotational penetrometers and operators was conducted on seven different surface types at the ASTM meetings in Atlanta in November of 2009. The results showed strong repeatability and reproducibility on the range of surfaces that were tested. The repeatability and reproducibility results were two to three times better than the results of the ASTM F1951-99 testing that was done using one set of ASTM F1951-99 equipment in 2008.   
7.   How was the “rotational penetrometer” developed?
In Phase I of the U.S. Access Board’s “Measurement of Surface Characteristics for Accessibility” project, dozens of devices designed to measure the firmness and stability were researched and evaluated. This included a broad range of items, including foods, human skin, golf course greens, and battle fields where tanks could potentially sink. Nothing was found that could measure surfaces ranging from level concrete to soft sand specifically for firmness and stability related to the load of a human being trying to ambulate or roll over a surface. Design specifications were established for the needed technology and over several years of research and development with many concepts, prototypes and refinements, the rotational penetrometer was created to meet all of the needed design criteria.
The development of the Rotational Penetrometer began in 1993 at Beneficial Designs with funding from a Federal National Institutes of Health (NIH) grant, the NIH NICHD NCMRR Phase I Grant # 1 R43 HD30979-01 Small Business Innovation Research (SBIR), titled: Measurement of Surface Characteristics for Accessibility.  Phase II was completed in July of 2000. During Phase II, the U.S. Access Board funded Beneficial Designs to conduct research with human subjects to look at the correlation of the results of human subject testing with the Rotational Penetrometer and the results obtained from using the ASTM F 1951 Wheelchair Work Measurement Method. The results of this work are summarized in the report Accessible Exterior Surfaces and is available on the U.S. Access Board website.
8. What is included in the surface provisions within the ADA/ABA Accessibility Guidelines for Play Areas?
Section 1008.2.6.1 requires that ground surfaces used on accessible routes, clear spaces, and turning spaces comply with ASTM F1951-99. Ground surfaces must also be inspected and maintained regularly and frequently to ensure continued compliance with this specification. ASTM F1951-99 is a test performed in a laboratory. It is not easily portable to perform the test method on an “installed” surface in the field. 
9. What are the advantages of using the rotational penetrometer over the ASTM F1951 laboratory test procedure?
The portability of the rotational penetrometer permits manufacturers, maintenance staff, owner/operators, and consumers the ability to evaluate the firmness and stability of any surfaces or surface systems in an installed interior or exterior setting. An individual can easily be trained and use the device in any location. It can be carried and moved by one person so that multiple areas can be tested at one site or many sites. The cost of the rotational penetrometer is a fraction of the cost of the laboratory equipment used to conduct the ASTM F1951-99 test procedure, thereby making it more readily available to facility owners.
10. But only one company makes the rotational penetrometer, does the proposed test method give the manufacturer an unfair market advantage?
The design of the rotational penetrometer was developed by Beneficial Designs, Inc., with funding from the National Institute of Child Health and Human Development (NICHD) at the National Institutes of Health (NIH) through Small Business Innovation Research Phase I Grant #1 R43 HD 30969-01 and Phase II Grant #2 R44 HD 30969-02. The device has not been patented. Non-patent of the device will allow for any company to manufacture the device and promote technological advancements in the design, such as possibly making it smaller, lighter and even more portable.
11. Does the operator for the rotational penetrometer need special training or certification?
No. The rotational penetrometer is a simple, easy to use instrument. The operator should be trained per the manufacturer’s recommendations.
12. How will the “rotational penetrometer” be used? 
 As a field test, the rotational penetrometer will provide the playground owner with objective measurements of “firmness and stability” of any given surface over time. The necessity and frequency of field testing will be dependent on a variety of factors such as surface material characteristics, visitor use, weather, etc. The information gained from using this field test will help to determine the level and complexity of maintenance. Where an operator is not satisfied with the readings, plans to improve the “firmness and stability” of the surface may commence.  
13. Is there “pass” or “fail” criteria?

Currently, the proposed test method put forth by the ASTM task group does not include performance criteria for any type of surface or surface system. Performance criteria can be established by organizations referencing the test method for specific types of surfaces or surface systems and the environment they are installed.
14. If a surface meets the ASTM F1951-99 Specification, is it approved under the ADA/ABA?

No. There is no approval process under the ADA and never has been. Information test results for ASTM F1951-99 regarding specific surfaces could assist a playground owner looking to purchase a surface for a play area required to be accessible.* After purchase and installation, the playground owner is required to ensure that the surface is maintained and inspected frequently to continue to meet the specifications. 

*The ADA does not cover play areas located in private residential or religious entities.   

15. Could the same type of surface material get different measurements using the rotational penetrometer? 

A baseline measurement should always be taken on a concrete or asphalt surface. This measurement should always be consistent +/- .02 inches based on the latest calibration of the device. The measurements taken on various surfaces are dependent on the type of surface material that is being tested. If the surface is a highly variable material, there will be a greater standard deviation based on the characteristics of the surface material.

For more information contact Jennifer Skulski at the National Center on Accessibility.