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Reprinted from:  http://www.landscapeonline.com/research/article/7249 

Natural Surfaces: Organic vs. Inorganic
By Dr. Arthur H. Mittelstaedt, Jr., Ed.D



Whatever material is chosen for under or around play equipment, it should conform to ASTM F1292 testing specifications. Image courtesy of Playworld Systems.

The use of natural surfacing materials or artificial surfacing under or around play equipment is a debate that continues to resurface. This article presents information published by the Consumer Product Safety Commission in the Handbook for Public Playground Safety, and opinions of the author based upon experience and education.

A review of the alternatives follows. It is necessary to fully understand the varied surfacings that have been used and are in use today. The “fall impact attenuating characteristics” have been left out as they depend upon laboratory testing in accordance with ASTM F-1292. The advantages and disadvantages have been edited and modified from the original CPSC list.

Organic Loose Material

(wood chips, bark mulch, etc.)

Installation/Maintenance

  • Should not be installed over existing hard surfaces (e.g., asphalt, concrete).
  • Requires a method of containment (e.g., retaining barrier, excavated pit at 6’ or more from equipment).
  • Requires drainage treatment underneath the surfacing material.
  • Requires periodic renewal or replacement and continuous maintenance (e.g., leveling, grading, sifting, raking) depending upon wear to maintain appropriate depth and remove foreign matter).

Advantages

  • Low initial cost.
  • Ease of installation.
  • Fair drainage.
  • Less abrasive than sand.
  • Less attractive to cats and dogs (compared to sand).
  • Attractive appearance.
  • Readily available.

Disadvantages

  • Conditions that may reduce cushioning:
  • Rain, high humidity, freezing temperatures.
  • Normal use and abuse, plus dirt and other foreign matter.
  • Decomposes, is pulverized and compacts requiring replenishment.
  • Depth may be reduced by displacement during play or by wind.
  • Can be blown or thrown into children’s eyes.
  • Subject to microbial growth when wet.
  • Conceals animal excrement and trash (e.g., broken glass, nails, pencils and other sharp objects).
  • Spreads easily outside of containment area.
  • Can be flammable.
  • Subject to theft.

Inorganic Loose Material

(sand and gravel)

Installation/Maintenance

  • Should not be installed over existing hard surfaces.
  • Method of containment needed (e.g., retaining barrier, excavated pit with perimeter 6’ or more from equipment.
  • Drainage required underneath surface material.
  • Requires periodic renewal or replacement and continuous maintenance (e.g., leveling, grading, sifting, raking) to maintain appropriate depth and remove foreign matter.
  • Compacted sand should periodically be turned over, loosened, and cleaned.
  • Gravel may require periodic break up and removal of hard pan or silt.

Advantages

  • Low initial cost.
  • Ease of installation.
  • Does not pulverize.
  • Not ideal for microbial growth.
  • Non-flammable.
  • Materials are readily available.
  • Not susceptible to vandalism except by contamination.
  • Gravel is less attractive to animals than sand.

Disadvantages

  • Conditions that reduce cushioning:
  • Rain, high humidity, freezing temperatures.
  • Normal use, dirt and other foreign matter.
  • Depth may be reduced during play and may be blown by wind.
  • May be blown or thrown into children’s eyes.
  • May be swallowed.
  • Conceals animal excrement, trash and dangerous objects (e.g., broken glass, nails, pencils).

Sand:

  • Spreads easily outside of containment area.
  • Small particles bind together and become less cushioning when wet; when thoroughly wet, sand becomes a rigid material; can be tracked out of play area on shoes; abrasive to floor surfaces when tracked indoors; abrasive to plastic materials.
  • Adheres to clothing.
  • Susceptible to fouling by animals.

Gravel:

  • Difficult to walk on.
  • If displaced onto nearby hard surface pathways can present a slipping hazard.
  • Hard pan may form under heavily traveled areas.



Photo courtesy of Grubble, LLC., Tierra Verde Industrial.

Inorganic Base Fill

(Synthetic) (shredded tires)

Installation/Maintenance

  • Should not be installed over existing hard surfaces.
  • Method of containment needed (e.g., retaining barrier, excavated pit at 6’ or more from equipment).
  • Drainage required underneath material.
  • Requires continuous maintenance (e.g., leveling, grading, sifting, raking) to maintain appropriate depth and remove foreign matter.

Advantages

  • Ease of installation.
  • Shock absorbing capability.
  • Not abrasive.
  • Less likely to compact than other loose-fill materials.
  • Not ideal for microbial growth.
  • Does not deteriorate over time.

Disadvantages

  • Flammable.
  • Unless treated, may cause staining of clothing.
  • May contain steel wires if generated from steel belted tires.
  • Depth may be reduced by play activities and requires replenishment.
  • May be swallowed.

Although the consumer Product Safety Commission classified some types of surface materials as organic loose material and inorganic loose material, other examples of natural materials presently used under playground equipment might be:

  • Softwood Bark—mini nuggets of bark
  • Hardwood Bark—shredded, unshredded bark
  • Cocoa Shell Mulch—shredded shells
  • Crushed Stone or Dust—1/16” mesh or crushed limestone rock
  • Dirt—natural or with sod or grass turf
  • Peat moss—natural material
  • Sawdust—residue from sawed wood
  • Corn cobs—ground cobs
  • Rubber granules or chips
  • Loam and root fiber
  • Stone grits
  • Marble chips and dust
  • Crushed stone dust
  • Fine crushed shells or coral
  • Cork and bark substances
  • Peanut shells and coffee bean shells
  • Sponge shredded coconut husks
  • Bluestone screenings
  • Brick screenings
  • Tan bark chips

The fall absorbing or impact attenuating characteristics of the organic and inorganic categories of materials have not been included, as the author’s opinion is that whatever material that is chosen by a purchaser for use should be on the basis of whether it is to be under or around play equipment or apparatus within the 6’ zone of safety, and thus subject to falls. If so, all materials should conform to ASTM F1292 laboratory testing specification for samples. Materials will vary, particularly loose fill organic and inorganic materials, depending upon the source. In the construction industry, materials are all subject to such ASTM standards thus providing a uniform safe product regardless of where mined, processed, manufactured or shipped to the point of use. The industry automatically includes such tests, be it sand or any other material used in construction. Thus, materials to protect children from injuries must be subject to the same tests throughout the country wherever the source may be.

There is no comparative analysis of these materials provided in any of the guidelines or standards. It is urged of owners and operators of playgrounds to re-evaluate their surfaces via testing, conducted on their surface (or a sample thereof) by a certified testing lab. It is the responsibility of the owner/operator to use materials that have been tested and certified to comply with the ASTM Standard F-1292 laboratory for impact attenuation. Now is the time for owner/operators to rethink and replan and more importantly, to budget for this change. However, the discussion or debate over toxicity and flammability of the surface material is heating up as well.