Hydrogen peroxide (CAS 7722-84-1): storage and disposal

Check the cap at the shelf, and do it by eye. Stronger solutions need a vented cap because the liquid keeps giving off oxygen, so a tight replacement lid on a 30% bottle is a fault that can end in a burst container. Keep it cool and out of direct light, in a separate oxidiser space on non-combustible shelving. Strong solutions oxidise organic material and can start fires, so paper, cardboard and wooden shelves are poor neighbours. Dust and metals speed up the breakdown as well. Keep it well away from acetone, acetic acid, acetic anhydride, peroxide forming ethers, activated charcoal, aluminium powder and calcium carbide, which can react dangerously. Dental bleaching stock should be held as a dated stock line, not in a drawer of mixed materials.

As it ages, hydrogen peroxide turns slowly into water and oxygen. That means an old 30% bottle may be weaker than its label says, but gas has been forming all that time. Watch for a bulging or sucked-in bottle, leaks around the cap, gas bubbles rising in the liquid and any stain on a shelf. Hissing on opening is a warning sign, though nobody should open it to find out. A label with an unclear strength matters too, since nobody can then say what it is. Crystals or a dry crust are not normal here and should be recorded. If stock is old, undated or showing any of these signs, do not move or open it, and get a specialist assessment.

Decomposes slowly to oxygen and water, and sealed containers can build pressure.

By specialist collection only. It never goes down the drain or into general waste. It is normally packed in a oxidising laboratory pack with compatible chemicals.

The code changes with the holder. A dental surgery, clinic or hospital uses 18 01 06*, a veterinary practice 18 02 05*, and a school or university lab pack 16 05 06*. Each marks hazardous waste, so a consignment note applies, but the strength and condition of the bottle matter far more to the people packing it. Give the label strength, or say it is unclear, along with bottle size and whether the cap is vented or bulging. It is grouped as an oxidiser, apart from flammable, organic and alkali stock. Specialist collection is the only route, including for a weak solution. Do not send it to a sink or drain or a general waste bin or skip, and never dilute or treat it beforehand.

Usually held as: 3%, 6%, 30%, dental bleaching strengths.

Part-used bottles and full containers are both fine. Tell us the size and how many, and an estimate is enough for a first price.