Foam performance depends on holding the concentrate-to-water ratio across the range of flows the system may see.

Too lean and the blanket is thin and breaks down under heat.

Too rich and the system exhausts its concentrate before the fire is out.

Bladder tanks, in-line inductors and balanced pressure proportioners are different answers to the same problem.

They differ in accuracy, cost and how wide a flow range they hold the ratio across.

Proportioning accuracy is verified during commissioning and periodically thereafter.

Water pressure squeezes a flexible bladder containing the concentrate, pushing it into the water stream.

It needs no separate pump or power supply for the concentrate.

That simplicity and reliability is why bladder tanks are widely used.

The bladder itself is the wearing component and is replaced periodically.

Tank refilling after a discharge is a specific procedure rather than simply topping up.

The tank is a pressure vessel and falls under pressure equipment rules.

Fuels containing polar solvents, which destroy an ordinary foam blanket by drawing water out of it.

Alcohols, ketones and esters all behave this way.

A system charged with the wrong concentrate produces foam that collapses on contact.

Fuel blends containing ethanol are a common and easily overlooked case.

Alcohol-resistant concentrates form a polymer membrane that protects the blanket.

Establishing what fuel is actually present is the first step in specifying a foam system.

Foam is fragile, and plunging it into a burning liquid breaks the blanket and mixes fuel into it.

Discharge onto the fuel surface is gentle wherever possible.

Foam chambers, pourers and monitors are designed to deliver foam onto rather than into the fuel.

Aspirating devices introduce air to expand the solution into finished foam.

Non-aspirating discharge produces a wetter, less stable blanket that suits some applications.

The device is selected with the concentrate rather than independently of it.

They are being restricted in many markets on environmental persistence grounds, and the position differs markedly between jurisdictions.

Transition to fluorine-free alternatives is underway in a number of regions.

It is not a simple substitution: performance characteristics differ.

Compatibility with existing proportioning and discharge equipment has to be checked.

Systems generally require cleaning before changeover, and disposal of the old concentrate is itself regulated.

The current local position should be established rather than assuming continuity from past practice.

They have shelf lives and are tested periodically for degradation.

Testing checks properties such as expansion, drainage and sediment.

Concentrate stored at high temperature degrades faster.

Sediment can block proportioning equipment as well as indicating degradation.

Testing is a scheduled task rather than a commissioning one.

Sampling procedures and acceptance criteria come from the concentrate manufacturer and the local standard.

Flammable liquid storage tanks, bunds, loading racks, aircraft hangars and some process areas.

Storage tank protection uses foam chambers or pourers delivering onto the liquid surface.

Bund protection covers spillage around tanks rather than inside them.

Loading and unloading areas are protected because that is where spills occur.

Aircraft hangars use foam-water deluge over very large areas.

Each application has its own design basis, and the standard in force locally governs the requirements.