Only for mineral deposits - limescale, urinal scale, rust and hard-water scaling. For grease and hair, caustic products are better and safer.

Acids dissolve carbonate and mineral scale, which alkalis cannot. In hard-water areas and in urinal and sanitary pipework this is a real and recurring problem that nothing else addresses.

Sulphuric acid products also attack organic material by dehydration, but that is a brutal way to solve a problem caustics solve cleanly.

For fat, oil, grease, soap and hair, choose caustic. For solid obstructions and roots, choose mechanical clearance.

If the deposit type is unknown, it is usually organic - mineral scale is characteristic of specific installations and water conditions rather than a general blockage cause.

Given the hazard profile, the default should be to avoid acids unless the case for them is specific.

They burn on contact, release heat and fumes when diluted or when they meet organic matter, and react violently with alkalis and hypochlorite.

Concentrated acids cause immediate and severe tissue damage. Eye exposure risks permanent loss of sight, and splash-back from a drain is the characteristic mechanism of injury.

Adding water to concentrated acid releases a great deal of heat very rapidly and can boil and spit the mixture. The rule is always to add acid to water, never the reverse.

Contact with organic material generates heat and often visible fuming, and in a confined drain this can force material back out of the opening.

Mixing with bleach or hypochlorite produces chlorine gas; mixing with caustic products produces a violent neutralisation reaction.

Fumes are corrosive to the airway and to surrounding fittings, so ventilation is required and the area should be cleared of other people.

Full chemical protective equipment - face shield over splash goggles, acid-resistant gloves and apron, covered skin, and eyewash immediately available.

This is not a product for ordinary cleaning PPE. A face shield alone is insufficient because it does not seal around the eyes; goggles alone leave the face exposed. Both are used together.

Gloves must be rated for the specific acid, with cuffs over the sleeve so nothing runs inside.

An apron or chemical suit protects the body, and footwear must not be absorbent.

Emergency eyewash and a means of copious flushing must be available before the container is opened, not fetched afterwards.

Ventilation is required. Working on a drain in a small, unventilated room with an acid product is a recognised cause of respiratory injury.

Anyone using these products should have read the safety data sheet and be trained; in many jurisdictions the supply is restricted to professionals for this reason.

Metals, cement and concrete, natural stone, chrome fittings and many finishes - and some acids attack particular plastics.

Metal waste pipe, metal traps and any metal components in the system are attacked directly. Cast iron, steel, copper and chrome are all vulnerable to varying degrees.

Cement-based pipe, concrete channels and mortar joints are dissolved by acids, which matters in older drainage systems and in gullies.

Natural stone, terrazzo and many tile grouts are damaged by splashes on the floor around the drain, and that damage is permanent.

Visible chrome wastes and finishes mark almost immediately.

Plastic tolerance varies by acid and concentration, and heat generated in use compounds the risk.

Establish what the drainage system is made of before use. In an unknown or mixed system, acid is a poor choice.

No - never dose a drain that has had caustic, bleach or any other product in it. The reaction can be violent.

This is the most dangerous sequence in drain cleaning, and it usually happens by accident: a product is tried, does not work, and something else is poured in after it.

Acid meeting caustic neutralises exothermically and can boil and eject the contents of the trap. Acid meeting hypochlorite produces chlorine gas.

Because the previous product may be invisible in standing water, anyone attending a problem drain must ask what has already been used.

Where the history is unknown, the safe route is copious flushing with water by someone equipped for splash exposure, or mechanical clearance.

In commercial premises, recording what has been dosed into which drain is a simple control that prevents this.

In many jurisdictions, yes - supply of concentrated acids is regulated, and several products are restricted to professional or trade purchasers.

Regulations covering the supply of concentrated acids to members of the public exist in a number of countries, driven by both safety and security concerns. They may require licensing, reporting of suspicious transactions, or restrict sale entirely.

Concentration thresholds and the substances covered differ by jurisdiction, so a product freely available in one market may be controlled in another.

Workplace chemical regulations add further requirements: risk assessment, safety data sheets, training, storage and exposure controls.

Discharge is regulated separately, since acid entering a sewer affects pH and may breach a trade effluent consent.

Establish the local position on supply, use and discharge before specifying these products for a site.

Regular preventive descaling with milder acid maintainers, water management, and removing the source of the scale rather than repeatedly dissolving it.

Urinal scale is largely uric salts and mineral deposits that build progressively. Once established it is hard; caught early it responds to much milder chemistry.

Scheduled dosing with a mild acidic maintainer prevents the hard deposit forming, which avoids ever needing a concentrated acid.

Enzyme and bacterial urinal products work on the organic component and are widely used in washroom maintenance programmes.

Water management matters. Waterless and low-flush urinals have different scaling behaviour and require the manufacturer's own maintenance regime - using a general acid product in them frequently damages the trap cartridge.

Where scale has already blocked a waste, mechanical removal of the pipe section is sometimes cheaper and safer than repeated chemical attack.