Is grass safe under a swing set?

No. Grass over soil offers almost no impact attenuation, and the thin layer that does cushion wears away under the swing within weeks, leaving compacted dirt. The CPSC handbook treats earth surfaces such as soil and grass as unacceptable under equipment. Grass is fine as the surrounding lawn, outside the use zone, and nowhere else.

Can I use regular bark mulch from the garden center?

Not as safety surfacing. Landscape bark and dyed chips have no controlled particle size, no ASTM F2075 testing and no ASTM F1292 impact report. They stay chunky instead of knitting into a firm mat, which hurts both impact performance and wheelchair access. Buy engineered wood fiber sold for playgrounds, with both documents attached.

What is wrong with CCA-treated wood chips?

CCA is chromated copper arsenate, a preservative used in older pressure-treated lumber. Ground into chips it puts arsenic-bearing wood into a material children handle and sit in. The CPSC handbook is explicit that CCA-treated wood should not be used as playground surfacing. If you are recycling old decking or landscape timbers into chips, do not.

Is gravel acceptable under playground equipment?

Only pea gravel, and only within its limits. The CPSC figures rate 9 inches of pea gravel to a 5 foot fall height and no higher. Larger crushed or angular stone does not displace on impact, it does not pass the accessibility test, and it is a choking and throwing hazard with young children. Do not use driveway gravel or crusher run.

Can I put rubber tiles straight on the ground?

No. Rubber tiles and poured systems are rated as an assembly that includes the base beneath them. Laid on soil, they settle unevenly, open gaps at the seams, trap water and lose the rating the manufacturer tested. They need a compacted aggregate or concrete base built to the manufacturer's specification, with drainage designed in.

What not to use as playground surfacing

The common thread

Every material on this page fails for one of three reasons, and it is worth naming them before the list, because they also work as a test for anything not on it.

It does not attenuate impact. A playground surface exists to reduce head injury in a fall from the highest designated play surface. That performance is measured by drop test under ASTM F1292². A material with no F1292 report at your fall height is not a safety surface, whatever it looks like. How surfacing works explains what the test is actually measuring.
It does not stay firm and stable. The 2010 ADA Standards require accessible routes into and through a play area, and the Access Board's guidance points at a surface that is firm, stable and slip resistant⁴. Loose stone, rutted dirt and chunky bark all fail that.
It brings its own hazard. Contaminants, sharps, wire, choking-size pieces, or a surface that gets hot enough to burn.

The list, and what to use instead

Material	Why it fails	Use instead
Grass and packed dirt	Negligible impact attenuation, compacts hard, ruts and puddles	Engineered wood fiber or a unitary system
Landscape or bark mulch	No sizing control, no F2075 or F1292 data, will not knit	Engineered wood fiber sold for playgrounds
CCA-treated wood chips	Arsenic-bearing preservative in a material children handle	Untreated virgin wood fiber
Gravel coarser than pea size	Does not displace on impact, fails accessibility, throwable	Pea gravel within its 5 ft limit, or wood fiber
Tire shred with exposed wire	Steel wire causes cuts and punctures	Clean shredded rubber processed to remove wire
Carpet or mats over hard ground	Cushions nothing, curls at the edges, holds water	A tested unitary system on a designed base
Asphalt and concrete	No attenuation at any fall height	Any rated surface, over the full use zone
Sand over a hard base	The base sets the result once the sand thins	Full-depth sand over a drained base, or a different material
Rubber on an unprepared base	Settles, opens seams, voids the tested assembly	The manufacturer's specified base build-up
Recycled material of unknown origin	No provenance, no contaminant testing, no rating	A product with current test documentation

Ten surfacing choices that fail, with the standard replacement for each. The right-hand column assumes the fall height and use zone have already been established.

Grass, dirt and the surfaces that are already there

Earth surfaces are the most common failure on private and community playgrounds, because nobody decides to use them. They are simply what is left when nothing was installed. The CPSC handbook treats soil and grass as unacceptable under and around equipment¹.

The mechanism is quick. Turf provides a thin, variable cushion. Under a swing or a slide exit it wears through in weeks, and what remains is compacted soil, which behaves close to a hard surface in a fall. The same spot then holds water, ruts, and freezes solid in winter. Playground injury causes covers where falls to the surface sit in the overall injury picture.

Bark mulch, playchips and free tree chips

Engineered wood fiber and landscape mulch look similar in a photograph and behave nothing alike. EWF is milled to a controlled particle size under ASTM F2075³ and screened for tramp metal and hazardous metals. Bark, dyed chips and ground pallet waste are none of those things.

The practical difference is knitting. Fibrous EWF consolidates into a firm mat that a wheelchair can cross and that still displaces under a heavy impact. Chunky bark never consolidates, so it fails the accessibility test and it rolls underfoot. Engineered wood fiber covers the spec and what to check on delivery.

Free chips from a tree service carry two extra problems: unknown species, including material that may be treated or diseased, and unknown contaminants from whatever else went through the chipper.

CCA-treated wood

Chromated copper arsenate was the standard preservative in pressure-treated lumber for decades. Old decking, landscape timbers and retired playsets built before the residential phase-out may contain it. The CPSC handbook is direct that CCA-treated wood should not be used as playground surfacing.

The temptation is real on demolition projects, where an old timber structure is coming out and a chipper is on site. Do not put that material back into the use zone. Timber rot and repair covers handling old treated lumber, and buying a used playset covers how to date a structure.

Gravel, and where the line sits

Pea gravel is an accepted loose fill within tight limits: the CPSC figures rate 9 inches compressed to a 5 foot fall height and stop there. Anything coarser or more angular is not a playground surface. Crushed stone and crusher run lock together rather than displacing, which is exactly what you want in a base and exactly what you do not want on top.

Pea gravel also brings its own issues at young ages: it is a choking size, it gets thrown, and it fails accessibility comprehensively. Sand and pea gravel covers the narrow cases where it still makes sense.

Tire shred with wire, and unknown recycled material

Shredded rubber is a legitimate playground surface when it is processed for the purpose: wire removed, sized consistently, and sold with an F1292 report. Unprocessed tire shred is a different product. Exposed steel belt wire in a surface children land on and dig in causes cuts and puncture wounds, and it is not something a visual inspection reliably finds once the material is spread.

The broader rule covers any recycled feedstock with no paperwork. If nobody can tell you what the material was before it was shredded, where it was processed, or what it has been tested for, it does not go in a use zone. Rubber mulch covers what a legitimate product looks like and what to ask a supplier.

Correct materials installed incorrectly

Three of the most expensive failures involve the right product and the wrong installation.

Carpet, gym mats or foam over hard ground. Thin resilient layers over concrete or compacted soil do almost nothing at playground fall heights. They also curl, hold water, harbor mold and trip people. Indoor products moved outdoors fail fastest of all. Indoor play surfacing covers where those products do belong.

Sand over a hard base. Sand works by displacing. Once it thins out, and it will thin out first under swings, what governs the impact is whatever is underneath. Sand laid directly on concrete or on a compacted clay pan is rated optimistically and performs badly at the exact spot where it matters.

Unitary rubber over an unprepared base. Poured-in-place systems and tiles are tested as assemblies. The manufacturer's F1292 report covers a specific thickness over a specific base. Install it over soil, over a base that was never compacted, or over ground that does not drain, and the tested assembly no longer exists. Settlement opens seams, water sits under the system, and the surface fails early. Drainage and base layers and installing playground surfacing cover the build-up.

What to use instead, briefly

For most sites the shortlist is short. Engineered wood fiber where budget is tight and maintenance is owned. Shredded rubber where maintenance is the binding constraint. Poured-in-place rubber or tiles where accessibility, durability or a high fall height is driving the decision. Artificial turf over a tested shock pad sits alongside those where appearance matters, and the pad, not the grass blade, is what carries the rating.

Whichever you pick, the depth or thickness comes from the fall height, not from a budget. Start at the depth and fall height chart, confirm the use zone area, and ask for the test documentation before the order rather than after the inspection. Surfacing test methods explains what those reports say and how a field test differs from a laboratory one.