Most brush cutter injuries to bystanders aren’t caused by the blade itself — they’re caused by whatever the blade or line throws before anyone realises what’s happening. A stone, a bit of wire fencing, a shard of glass hidden in long grass: all of it becomes a projectile the moment it meets a spinning cutting attachment, and it travels a lot further than most people expect.
Why 15 metres is the standard
Every reputable manufacturer — Stihl, Husqvarna, Makita and others — states a minimum bystander exclusion zone of 15 m around a running brush cutter in their operator manuals. This isn’t a legal minimum invented by a safety committee; it’s based on measured throw distance during testing with metal blades at full rated speed.
The 15 m zone applies to:
- Other people, including anyone just walking past or curious about the noise
- Pets and livestock
- Parked cars, sheds, greenhouses and windows
- Yourself, once you’ve stopped and are walking back through cut material
The distance shrinks the risk but does not eliminate it entirely — a hard stone strike can still occur just outside 15 m in rare cases, which is why direction of cut and attachment choice matter as much as raw distance.
What actually gets thrown, and how fast
The cutting attachment is the variable that matters most. A nylon line head throws lighter debris at lower velocity than a metal blade, but it still moves fast enough to cause eye injuries and skin lacerations at close range.
| Attachment | Typical tip speed | Realistic throw hazard | Exclusion zone |
|---|---|---|---|
| Nylon line (bump-feed head) | ~80-100 m/s | Small stones, grit, cut plant debris | 15 m |
| 2 or 3-tooth metal blade | ~70-90 m/s | Stones, wire, glass, metal fragments | 15 m |
| Multi-tooth (8-tooth+) blade | ~70-90 m/s | Larger stone fragments, sharper edges | 15 m |
| Saw blade / brush blade attachment | ~60-80 m/s | Wood splinters, bark, larger fragments | 15 m (20 m recommended near solid obstacles) |
Safety note: A stone thrown by a metal blade at these speeds can crack a car windscreen or punch a hole in single-glazed glass from well within normal garden distances. Treat any window, car or greenhouse within the work area as a hard boundary, not a suggestion.
Wire is a particular hazard because it doesn’t behave like a stone — it can whip back toward the operator as well as forward, and it’s the main reason for wearing full-face visor protection rather than just safety glasses.
Checking the area before you start
Do this every time, not just on unfamiliar ground. It takes two minutes and it’s the single most effective thing you can do to prevent a thrown-object injury.
- Walk the entire area you’re about to cut, at walking pace, looking down.
- Remove or flag anything solid: stones, glass, cans, wire offcuts, tent pegs, sprinkler heads.
- Note anything you can’t remove — a rockery edge, a manhole cover, buried fence wire — and plan your cutting direction to throw away from it, not toward it.
- Check for anything living in the grass: hedgehogs, ground-nesting birds, a cat that likes to sit in long grass. Give these areas a wide check even if you plan to strim close.
- Identify every window, parked vehicle, greenhouse and outbuilding within 20 m and confirm your cutting line won’t send debris toward them.
- Confirm the 15 m zone around your work area is actually clear of people and pets before starting the engine, not just when you first look up.
Pets, children and pedestrians
Pets and small children are the highest-risk group because they don’t understand the danger and won’t reliably stay where you leave them.
- Dogs and cats should be indoors or securely confined well outside the 15 m zone — not just tied up, since a startled animal on a lead can still be within throw range.
- Children need active supervision by a second adult, not just “stay over there.” A child’s attention span for staying put is measured in seconds.
- On a property with a public footpath, driveway or shared access, treat every approach as a potential bystander entry point. Stop cutting before someone reaches the 15 m line, not after.
- Livestock and grazing animals should be moved to a separate paddock or field before you start, since fencing alone won’t stop a startled animal moving toward the noise.
Safety note: If a person or animal enters your exclusion zone while the engine is running, release the throttle fully and wait for the cutting attachment to stop completely before doing anything else — waving, shouting or turning around with a still-spinning blade is how bystander injuries actually happen.
Working with a partner
A second person is genuinely useful on any job near a road, footpath, or blind corner — somewhere you can’t maintain a clear line of sight over the whole work area yourself.
- Agree hand signals before starting, since normal speech is useless over engine noise at working distance.
- The spotter’s job is to watch the areas you can’t — behind you, round hedges, over walls — and to intercept anyone approaching before they reach the 15 m line.
- The spotter should stay outside the exclusion zone themselves, at the edge where they can still see you and any approach routes.
- Never rely on a spotter as a substitute for stopping the engine when someone does get close. Their job is early warning, not last-second intervention.
Windows, cars and structures
Glass and paintwork don’t need to be hit hard to be damaged — a single stone at blade speed is enough to crack a pane or chip a windscreen. When cutting near any of these:
- Work parallel to the window or vehicle rather than facing toward it where possible, so any thrown debris travels along the wall line rather than directly at the glass.
- For greenhouses and cold frames, increase your working distance beyond the standard 15 m if you’re using a metal blade, since the panes are usually thinner than house windows.
- Move cars, if you can, rather than trusting distance alone — a chipped windscreen or paint strike is expensive and entirely avoidable.
- Close ground-floor windows and doors on the side facing your work area.
Quick checklist
Run through this before every session, not just the first one on a new job:
- Area walked and cleared of stones, wire, glass and debris
- 15 m exclusion zone confirmed clear of people, pets and livestock
- Windows, cars and greenhouses within 20 m identified and cutting direction planned around them
- Children and pets confined well outside the zone, not just “told to stay back”
- Spotter briefed and hand signals agreed, if working near a road or public path
- Full-face visor and correct PPE on before the engine starts, every time
When to stop and rethink
If the site genuinely can’t give you 15 m of clearance — a narrow side passage, a shared driveway, a garden backing directly onto a busy footpath — don’t try to compensate with a lower attachment speed or a “quick pass.” Switch to a line head at reduced throttle for the tightest sections, work in short bursts with full stops between passes, or hand-clear the area with shears instead. No job is worth a stone through next door’s window or, worse, an injury to someone who had no idea you were even out there.