The single most common defect we find on existing playgrounds in Vietnam is not broken equipment. It is safety surfacing that was chosen by budget rather than by the height of the equipment standing on it. A slide does not become safe because the brochure says so. It becomes safe when the surface underneath it is specified to absorb a fall from that specific height.
This article explains how that calculation works, why the wrong surface fails an inspection, and what an owner should ask for before signing off a bill of quantities.
What free height of fall actually means
Free height of fall is the vertical distance between the highest part of the equipment a child can stand on, and the surface below. It is not the total height of the structure. On a combination unit, the platform a child stands on may be 1.5 m above the ground while the roof above it reaches 2.6 m. The figure that drives the surfacing specification is 1.5 m.
The international reference for this is the EN 1176 and EN 1177 family of standards, which most Vietnamese specifications either adopt directly or mirror. EN 1177 defines the test for impact attenuation, measured as Head Injury Criterion. A surface passes at a given critical fall height when the measured HIC value stays below 1000 for a drop from that height.
The rule that matters: the critical fall height of the installed surface must be equal to or greater than the free height of fall of the equipment above it. If equipment allows a 2.0 m fall, a surface rated for 1.5 m is a defect, not a saving.
Typical surface options and what they achieve
The figures below are typical performance bands for materials as supplied in Vietnam. Actual values must come from the specific product test certificate, not from a general table.
| Surface | Usual thickness | Notes |
|---|---|---|
| Rubber safety tile | 25 mm to 100 mm+ | Thickness scales with the fall height. Thin decorative tiles are not safety surfacing. |
| EPDM wet pour | Base layer plus wear layer | Seamless, good for complex shapes. Performance sits in the base layer, not the coloured top. |
| Artificial grass with shockpad | Pad thickness governs | Grass alone provides almost no attenuation. The pad underneath does the work. |
| Loose fill such as sand or bark | 300 mm compacted depth typical | Cheapest to install, highest maintenance. Depth reduces with use and must be topped up. |
| Concrete, tile, compacted earth | Not applicable | Never acceptable under equipment with any fall height. |
Why the coloured top layer misleads buyers
On a wet pour installation the visible surface is a thin coloured wear layer, often 10 mm to 15 mm. Underneath sits a thicker black base made from recycled rubber, and that base is what absorbs the impact. Two installations can look identical on handover day while one has half the base thickness of the other.
This is the most frequent place where a project quietly loses its safety margin. Ask for the base layer thickness in writing, and ask for a core sample or a thickness measurement at handover rather than accepting a visual inspection.
The fall zone is as important as the surface
Impact-absorbing surfacing has to extend far enough around the equipment to catch a child who does not land directly below. For most static equipment the fall zone extends at least 1.5 m in every direction from the equipment. For swings and other moving items it is calculated from the length of travel and is considerably larger.
A common and expensive mistake is to install the correct surface but not enough of it. When the fall zone is undersized the installation fails inspection even though the material specification was right, and correcting it means lifting and re-laying the perimeter.
Vietnamese conditions change the calculation
Two local factors are routinely overlooked.
Drainage. Monsoon rainfall does not soak away through a sealed rubber surface if the sub-base beneath it has no route out. Water then sits between the base and the sub-base, the bond fails, and the surface lifts within one or two seasons. Drainage design belongs in the surfacing specification, not in a separate civil works scope that nobody coordinates.
Ultraviolet exposure and heat. Direct sun at surface temperatures well above ambient degrades cheap binder quickly. A wet pour laid with an under-specified binder becomes brittle, then crumbles at the edges, then fails as a safety surface while still looking mostly intact from a distance.
What to ask for before you sign
- The free height of fall for every item of equipment in the layout, listed individually.
- The critical fall height of the proposed surface, with the test certificate for that product.
- The base layer thickness, stated separately from the total thickness.
- A fall zone drawing showing the surfaced area around each item.
- The drainage detail beneath the surfacing.
- A commitment to thickness verification at handover.
None of these requests adds cost to a properly specified project. They only add cost to one that was going to be under-specified, which is exactly the point of asking.
How Heritage Horizon handles this
Because we design, supply and install under one contract, the fall height calculation, the surface selection and the installed result are the responsibility of a single party. There is no gap between the consultant who drew the layout and the contractor who laid the surface, which is where this particular defect usually appears.
Every handover includes the fall height schedule, the surface test certificate and a measured thickness record, so the owner can defend the installation at any inspection.