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Chainsaw dynamics & arborist PPE

Reactive forces and how to stay ahead of them, starting and brake rules, felling hinge basics, and the PPE standards your gear should actually meet.

Reactive forces

The saw pushes back on you every time it cuts. Which direction depends on which part of the chain is in the wood.

Force	What causes it	What the saw does	How you stay ahead
Kickback	The upper quadrant of the bar nose — the kickback zone — contacts wood or the chain pinches there	Bar snaps up and back toward your face and shoulder in a fraction of a second	Know where the nose is at all times, keep the tip out of the cut, use reduced-kickback chain, thumb wrapped, elbow locked, body out of the bar plane
Pushback	Cutting with the top of the bar (pulling chain) and the wood pinches	Saw is driven straight back toward the operator	Anticipate pinching, use wedges, keep a firm two-hand grip and stable stance
Pull-in	Cutting with the bottom of the bar and the chain grabs, or the spikes are not set	Saw is pulled forward, away from you, into the wood	Set the bumper spikes, start the cut at full throttle, expect the pull

Never cut with the nose of the bar unless you have been trained in bore cutting — and then only with the correct quadrant.

Drop-starting — dropping or swinging the saw to start it with one hand — is prohibited. It is a common source of severe leg and hand injuries and violates accepted safe practice.
Ground start: saw on firm level ground, chain brake engaged, one hand on the front handle, one foot through or on the rear handle, then pull.
Leg-lock start: rear handle clamped firmly between your thighs or knees, brake engaged, front handle held down, then pull. Use when there is no clear ground.
Start the saw at least 10 ft (3 m) from the fuelling point, never where fuel was spilled.
Aloft: the saw must be started with the brake on and secured to the climbing system or a dedicated saw lanyard before use, and the brake reapplied every time it leaves the cut.

Test the brake at the start of every shift: run the saw at idle on the ground, engage the brake, then briefly throttle — the chain must not move.
Confirm the inertia function by engaging the hand guard forward and checking it latches crisply.
A brake that drags, does not latch, or lets the chain creep takes the saw out of service — tag it.
Engage the brake before every step, every hand-off and every move aloft, not just between trees.

Assess lean, crown weight, defects, wind and escape routes before cutting. Choose the fall direction the tree will accept.
Cut a face notch (open face, conventional or Humboldt) to roughly 20–25% of the trunk diameter, with both cuts meeting exactly — a bypassed face cut destroys hinge control.
Leave hinge (holding) wood of even thickness across the stump, usually around 10% of diameter, and never cut through it. The hinge steers the tree.
Leave a back strap or use wedges and a pull line to control the release on leaning or heavy-crowned trees.
Clear two escape routes at roughly 45° back from the fall line, and use them — most struck-by injuries happen within a few feet of the stump.
Never fell with anyone inside two tree lengths, and never fell toward a conductor, structure or road you have not controlled.

Chainsaw chaps and trousers are tested to ASTM F1897 in the US; ASTM F3325 covers arborist-specific chainsaw-protective clothing for climbers.
European gear is marked to EN 381 / EN ISO 11393 with a class (class 1 = 20 m/s chain speed, class 2 = 24 m/s).
OSHA requires leg protection for ground chainsaw operation in logging work; employer policy and ANSI Z133 drive arborist practice aloft.
The pad works by pulling fibre into the sprocket to stall the chain — any cut, oil saturation or crushed padding retires the garment.
Coverage matters: chaps must wrap the full front of the leg and reach the boot top.

Helmets: ANSI/ISEA Z89.1 Class E (electrical, tested to 20 kV) and non-conductive for any work near conductors; climbing helmets are usually also certified to EN 12492 for retention and side impact.
A four-point chin strap keeps the helmet on during a fall, a swing or a struck-by event — a hard hat that leaves your head protects nothing.
Eye protection: ANSI Z87.1 rated glasses, goggles or a mesh screen. Mesh sheds sawdust but not fine debris — glasses under mesh for chipping work.
Hearing protection: earmuffs or plugs whenever a saw, chipper or blower runs; ANSI Z133 requires hearing protection in noise-exposed work.
Replace any helmet that has taken an impact or shows cracking, chalking or UV damage, and follow the manufacturer's service life.
High-visibility clothing for roadside work, snug sleeves, no loose drawstrings near the chain, and gloves appropriate to the task.

PPE is the last line, not the plan. Positioning, cut sequence and a real briefing prevent the injury PPE only reduces.

Follow your saw manufacturer's manual and your employer's safe work procedures — they override any general summary.
Never cut above shoulder height, one-handed, or with a saw you cannot control with both hands and a secure stance.
Aloft, always two attachment points when a running saw is in your hands, and trace your rope before every cut.