Levels, Squares & Chalk Lines
Layout tools look harmless, but they cause cuts, eye injuries, falls and, when they’re inaccurate, expensive mistakes that make other hazards worse. A wall that isn’t plumb, a stair that isn’t square or a cut that’s off can lead to rework, forced cuts and unsafe structures. Good habits keep the tools accurate and the people using them safe.
- Carpenters
- Masons
- Framers
- All Trades
Common layout tools
- Spirit (bubble) levels in lengths from a few inches to 8 feet, in wood, aluminum or plastic. Torpedo levels are short and fit in a pouch.
- Laser levels project a dot, line or rotating plane for leveling, plumbing and layout across a room or site.
- Squares: speed squares (rafter squares), framing squares, combination squares and T-squares check and mark 90 and 45 degree angles.
- Plumb bobs are weights on a string that show true vertical.
- Chalk lines snap a straight line over a long distance using a chalk-coated string.
- Straightedges and string lines for masonry and long runs. See Tape Measures for measuring.
Hazards
- Cuts and punctures: squares have sharp edges and points, and aluminum levels can have burrs. Chalk line hooks and plumb bob tips are sharp.
- Falls and awkward reach: checking plumb overhead or leveling from a ladder, scaffold or edge. Carrying long levels on a ladder is a common cause of falls. See Ladder Basics.
- Laser eye hazards: a laser beam can injure the eye, and some bright lasers are classed as hazards at close range. See below.
- Dropped tools: a level or plumb bob dropped from height can injure someone below. See Tool Tethering.
- Chalk dust: blue chalk and red chalk are not toxic in small amounts, but dust irritates eyes, and chalk is slippery on smooth floors. Some colored chalk lines are permanent on porous surfaces.
- Trip hazards from strings, line levels and chalk lines stretched across walkways. See Slips, Trips & Falls.
- Inaccurate tools lead to bad work, which can mean unsafe stairs, railings, forms or framing.
Using levels and squares safely
- Check accuracy. Test a spirit level by marking a line, flipping the level end-for-end and checking that the bubble reads the same. Check a square by drawing a line from a straight edge, flipping the square and comparing. Replace or adjust tools that are off. Dropped or bent tools should be tested again.
- Keep tools clean and undamaged. Wipe off mortar, concrete, paint and dirt, which damage vials and edges. Don’t use a level as a pry bar, hammer or straightedge for a utility knife.
- Cut safely along squares. Don’t cut toward your hand, and use a clamp or a hold-down. For marking, use a pencil, not a knife, unless you’re trained and use the safe way. See Utility Knife.
- Carry long levels and squares safely. Carry them at your side, not over your shoulder in tight places, and never climb a ladder carrying one in one hand. Hoist with a rope or pass it up. See Extension Ladders.
- Hold the tool close and don’t reach out past your balance. Move the ladder rather than overreach.
- Secure tools at height. Use lanyards or hang them so they can’t fall, and don’t leave levels on ledges, scaffolds or ladders. See Tool Tethering.
- Store flat or hung, in a protective case or a place where they won’t be bent, stepped on or hit. Keep point protectors on squares and plumb bobs.
Laser levels
- Most construction lasers are low-power products (Class 2 or 3R) that can cause eye damage with direct staring over time. Higher-class lasers (3B and 4) are dangerous and need safety controls. See RF, Microwave & Laser Hazards.
- Never look directly into a laser beam or point it at anyone, including from reflective surfaces. Set the laser above or below eye level where possible.
- Use the laser manufacturer’s instructions, and turn the laser off when not in use. Don’t remove warning labels.
- Use laser detectors and receivers outdoors, since the beam is hard to see in bright light. Don’t use laser glasses made for viewing the beam as safety eyewear unless rated for it. See Laser Safety Eyewear.
- Keep the tripod stable, level and out of walkways, and don’t leave it where vehicles can hit it.
- Follow your company program and site rules, since lasers used for alignment of heavy equipment or in public areas may need more controls.
Chalk lines
- Snap away from your face and eyes, and wear safety glasses. Chalk can fly, and the string can snap back. See Eye & Face Protection.
- Keep the hook secure so it doesn’t pop loose and fly at someone. Use a helper, and warn them before snapping.
- Choose the right chalk color. Blue is easy to clean off, while red is more permanent. Use removable colors on finished surfaces.
- Don’t leave strings across walkways. Mark the line and remove the cord, or keep it high and visible.
- Close the case to keep chalk dry and keep it from spilling. Spilled chalk is slippery.
- Don’t use chalk lines near live wires or in wet areas without checking hazards. See Overhead Power Lines.
Layout checklist
- I tested my level and square for accuracy and replaced any that are off or damaged
- I carry long levels safely and never climb a ladder with one in my hand
- I tether or secure tools used at height
- I never look into or point a laser at anyone, and I use the laser as the maker directs
- I wear safety glasses when snapping chalk lines and keep strings out of walkways
- I store layout tools flat, clean and protected
Standards & references
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