Polyethylene for general cleaning chemistry, polypropylene for a wider chemical range and warmer contents - and check compatibility for anything aggressive.

High-density polyethylene is the commodity material: cheap, tough, and compatible with most detergents, disinfectants and general cleaners.

Polypropylene handles a broader chemical range and higher temperatures, and is stiffer, which suits bottles that take a trigger with a firm action.

Both are attacked by some solvents. Aromatic and chlorinated solvents in particular cause swelling, softening or crazing, and the bottle fails without much warning.

Chemical suppliers publish compatibility data, and it is worth checking before committing to a bottle for anything beyond ordinary cleaning chemistry.

Signs a bottle is failing: it feels soft or tacky, the wall has become cloudy or crazed, it has changed shape, or it has become brittle enough to crack when squeezed.

Yes - it determines which triggers fit, and standardising on one size lets bottles and triggers be replaced independently.

Bottle necks are specified by diameter and thread finish, and the common cleaning sizes are a small set.

A site running several neck sizes ends up discarding serviceable bottles because the spare triggers do not fit, and vice versa.

Triggers fail far more often than bottles, so being able to replace just the head is a genuine saving.

It also matters for the dip tube: a trigger designed for a taller bottle has a longer tube, and fitted to a short bottle it kinks against the base and stops drawing.

When standardising, check what the chemical supplier's own bottles use - matching them means empty product bottles can be reused as spares.

A mid-size bottle for general work - large enough to last a shift, light enough to hold and trigger repeatedly.

Weight is the constraint. A large bottle full of solution is tiring to hold at arm's length while operating a trigger, and hand fatigue leads to poor technique and fewer sprays applied where they are needed.

Small bottles are comfortable but run out mid-task, which sends the operator back to the dilution station.

Most commercial cleaning uses a bottle sized to fit a caddy, which effectively sets the capacity.

For larger areas, a pump-up sprayer holding several litres is the right tool rather than a bigger trigger bottle.

Standardise on one or two sizes so that labels, caddies, storage and dilution station settings all match.

Because a diluted chemical in an unmarked container is both a real safety hazard and, in most jurisdictions, a breach of workplace chemical regulations.

Workplace chemical regimes generally require containers of decanted or diluted product to identify the contents and carry the relevant hazard information.

The practical hazards are direct: unlabelled bottles are used on the wrong surface, mixed with something incompatible, or - occasionally and seriously - drunk.

The simplest control is a label for every outlet on the dilution station, so filling a bottle and labelling it become one action.

Labels must survive the environment. Paper labels in a wet area become unlabelled bottles within a week, so waterproof labels or printed bottles are worth the difference.

Colour coding reinforces labelling but does not replace it, since a colour does not convey hazard information.

Only after thorough cleaning, and never for a chemical incompatible with the residue - and the old label must come off or be replaced.

Residue of one product mixing with another can neutralise it, react, or in the worst case produce hazardous gas. Chlorine and acid residues are the dangerous combination.

Even where the chemistry is safe, contamination degrades performance - detergent residue neutralises quaternary sanitizers, for instance.

The old label is a serious problem. A bottle still labelled as one product but holding another is worse than an unlabelled bottle, because it actively misleads.

Never reuse a food or drink container for chemical, and never use a chemical bottle for anything consumable. This causes poisonings every year.

Where bottles are reused routinely, a documented rinse procedure and a relabelling step should be part of it.

Upright, closed, below eye level, segregated by incompatibility, and out of direct sunlight.

Upright and closed prevents leaks and evaporation and stops the trigger dripping onto the shelf below.

Below eye level matters: reaching down a container of chemical from above head height is how facial and eye exposure happens.

Segregate incompatible products, particularly keeping chlorine-based products away from acids.

Sunlight degrades both the plastic and many actives - chlorine solutions in particular lose strength quickly in a sunlit store.

Do not store diluted solution long-term. Many made-up solutions have a short in-use life, and a bottle left for weeks may be well below strength.

Keep the store locked or restricted where the public, patients, residents or children could otherwise reach it.

Chemical attack on the resin, ultraviolet embrittlement, and being dropped - usually in that order.

Chemical attack shows as softening, swelling, crazing or a bottle that has changed shape. It develops over weeks and the failure is often a split while full.

Ultraviolet exposure embrittles plastic over time, so bottles stored in sunlight crack on impact when a new one would flex.

Drops are the mechanical cause, and a bottle already embrittled by chemical or ultraviolet exposure cracks where a fresh one bounces.

The neck thread is a specific weak point, and a cross-threaded trigger cracks the neck so the bottle leaks under the head.

Inspect bottles when refilling. It takes seconds and it is the moment a failing bottle is visible, before it is carried through a building full of chemical.