Freeze-Thaw: Refreezing & Slip Hazards

It's +6 °C at lunch and you're walking easy. By the time you leave 5 hours later, those wet areas turn into a sheet of black ice and are a high risk of someone falling.

The hazard

In March the days warm up and the nights drop below zero. Snow and ice melt, the water runs across walkways and decks, then refreezes into thin, clear ice you can't see. A fall on a hard slab does real damage, and the surface that was fine at noon is the one that catches you at dusk.

What to do

• Somebody owns the surfaces, all shift. Work areas, the routes to them, and scaffold platforms in use have to be kept clear of snow, ice, and anything else slippery, and sanded regularly. Assign who's checking and re-treating as conditions change, and close a route that can't be made safe yet.
• Re-check in the afternoon and at end of day. The temperature drop is predictable; the ice that follows it should be too.
• Keep sand or grit at the gangboxes and entrances, and get it on ramps, stairs, and the high-traffic paths before they glaze.
• Clear the water before it becomes ice. Squeegee or shovel off pooling and ridges — that's the cheapest fix available.
• Winter boots with deep tread. Traction devices where the site assessment says they help — and off before you go on a ladder, onto smooth indoor flooring, or into a vehicle.
• Short and slow steps, hands free.

Watch out for

• Black ice — a clear film on concrete, steel plate, and anywhere shaded that never sees sun.
• Meltwater dripping off scaffold, roofs, and forms that freezes in the same spot every single night.
• Sand and grit running low. Say something before it's empty, not after.
• The route you walked safely this morning being a different route by four o'clock.

Talk it over

• Where on this site refreezes first once the sun drops, and who's checking it?
• Who restocks the sand and the cleats, and do we have enough to get through the week?