Protrusions, projections and entanglement

What counts as a protrusion

A protrusion, or projection, is anything that sticks out from a play surface far enough to catch clothing or to injure a child who strikes it. The CPSC Public Playground Safety Handbook and ASTM F1487 treat it as two separate hazards with one test¹².

The impact hazard is blunt: a child falls or runs into a projection and it concentrates the force into a small area. The entanglement hazard is worse, because it does not depend on the size of the projection at all. A stub the size of a thumbnail is enough to catch a drawstring, a scarf, a necklace or a backpack strap. If the child's body is already in motion, downward off a slide or a pole, the clothing holds and the neck takes the load.

That second mechanism is why the rules look disproportionate to anyone seeing them for the first time. Two threads of a bolt is a fail. A hook with a gap you can barely see is a fail.

The projection test and the gauges

ASTM F1487 specifies a set of protrusion gauges, flat plates with holes of defined sizes². A certified inspector carries them, and the test is simple to describe:

1. Place the gauge over the projection so the projection enters the hole.
2. If the projection passes fully through the hole and still stands proud of the outer face of the gauge, it fails.
3. Apply the gauge in the direction a child would travel, not just perpendicular to the surface.

That last step is the one people miss. A bolt head on a vertical post is tested differently depending on whether a child slides past it, falls onto it or walks into it. On slides and poles the test is applied along the line of travel, because that is the direction that turns a projection into a hook.

S-hooks, open hooks and suspended hardware

Anything that hangs is inspected twice: once for wear and once for the gap. An S-hook is considered closed when the space between the tip and the body of the hook is no greater than 0.04 inch, commonly checked by trying to slide a dime into it¹. Open hooks, hooks with no closing action at all, do not belong on public equipment anywhere a child can reach them.

Two habits cause most failures here. The first is closing an S-hook with slip joint pliers, which crushes the hook out of round and leaves a gap on one face. Use the crimping tool the manufacturer supplies. The second is reusing an S-hook that has already been opened and closed a few times, which work hardens the steel and puts a crack at the bend.

Chain wear belongs in the same inspection. Links wear from the inside at the hanger and at the seat, the two ends that articulate every cycle. A chain that looks fine from six feet away can be half its original section at the top link. Hardware and fasteners sets out replacement intervals, and swing safety covers the specific loads on a swing chain.

Clothing is half the hazard

You cannot design out every projection, and you cannot stop children climbing. What you can change is what a child is wearing when they do.

The drawstring problem is well documented enough that the CPSC pursued it as a product issue: cords at the hood and neck of children's upper outerwear are treated as a substantial product hazard in the US, and mainstream children's clothing sold there no longer carries them. Imported, handmade and secondhand garments still do, and so do adult size hoodies worn by older children.

Bike helmets are the other one worth repeating to parents. The handbook says plainly that helmets should be removed before playing on equipment¹. The strap that makes a helmet safe on a bike is the same strap that holds a child against a climber.

For supervision routines that actually catch this before a child is at the top of a structure, see supervision.

Sharp points, edges, crush and shear

The same inspection pass picks up three related families of hazard.

Sharp points and edges. No accessible edge should be capable of cutting skin, and no point should be capable of puncturing it. In practice this means exposed bolt threads, cut chain link fence, split plastic on slides and panels, delaminated plywood, corroded steel at the ground line, and the raw edge where a vandalized part was torn away. Plastic is the surprise here: polyethylene that has gone chalky and brittle from ten or more years of UV cracks into edges that are genuinely sharp.

Crush and shear points. Any place two moving parts, or a moving part and a fixed part, come close enough to trap a finger or a hand. Seesaw pivots, gate hinges, spring rider joints and the moving deck of a spinner all qualify. The standard approach is to enclose the pivot or to keep the clearance large enough that a limb passes through without contact. See seesaws and rockers and spinners and orbiters for how those specific mechanisms are meant to be guarded.

Pinch points in hardware. Spring clips, quick links and turnbuckles left in a partly open state on nets and ropes. These often appear after a repair rather than at installation, which is why post repair inspection matters as much as the original handover.

A field test with what you have

A full gauge set is the right tool, and the entrapment and hazard checklist is built around one. For a backyard set or a first pass, two proxies get you most of the way.

• A dime. Try to insert it into every S-hook gap and every connector. If it enters, the hook is open.
• A cotton bandana or a length of cord. Drag it, under light tension, along every surface a child descends: the slide chute from hood to exit, the pole from grab point to ground, the upper deck edges, the overhead ladder end supports. Anything that catches the cloth will catch a hood cord.

The cloth drag test is the single most useful ten minutes you can spend on an older structure. It finds worn plastic lips, backed out screws and bent brackets that a visual check walks straight past.

Record findings with a photo, a location and a measurement, then match the fix to the cause. Backed out hardware means re-torque and thread lock, not a longer bolt. Missing caps mean a bag of the right caps. Split plastic means a replacement panel, because filler and tape do not survive a season outdoors. Vandalism and repairs covers the cases where the damage was deliberate.

What to do next

Fold the dime check and the cloth drag into the routine pass described in daily and weekly checks, because both take minutes and both catch hazards that develop between annual audits. If you are specifying new equipment, ask suppliers how bolt ends are finished as a purchasing question, since domed nuts and captive caps cost almost nothing at build time and a great deal to retrofit. And if you are choosing materials for a site with heavy sun or salt air, materials, steel, wood and plastic explains which ones turn into sharp edges first.