Understanding the Use and Working of Foam Monitors in Firefighting

When a petrol tank, a solvent store or a tanker spill catches fire, water alone often cannot put it out. The burning liquid floats on the water and keeps burning, and the water may even spread it. What firefighters need is a blanket of foam over the liquid’s surface, delivered from a safe distance. That is the job of a foam monitor.

What a foam monitor is

A monitor is a large nozzle on a swivel mounting that throws a powerful stream of water or foam solution a long way, far further than a hand-held hose. Monitors are fixed at refineries, tank farms, chemical plants and jetties, mounted on fire tenders, or set up on wheeled trolleys. They can be aimed by hand with a lever or wheel, by remote control, or automatically in some fixed systems. This lets a crew fight a big fire without standing in the heat.

How it works

1. Proportioning. Foam concentrate is mixed with water in the right ratio, usually upstream of the monitor by an inductor or proportioning system, or through a pick-up tube at the monitor itself. Getting the ratio right matters; too little concentrate gives weak foam.
2. Pressure. The monitor is driven by the water pressure from the fire pump or fire tender. It does not have its own pump.
3. Aeration. As the solution passes through the nozzle, air is drawn in and mixed, so the foam expands into bubbles.
4. Delivery. The stream is aimed so that the foam lands gently and spreads across the burning surface, for example by bouncing it off a tank wall, rather than plunging into the liquid.

The foam blanket smothers the fire by keeping air away from the fuel, stops flammable vapour rising from the surface, and cools the fuel with the water it contains.

Where foam monitors are used

• Oil and gas installations: refineries, petroleum depots, tank farms and pipeline stations.
• Chemical plants and solvent stores.
• Airports and hangars, where aviation fuel spills are the main fire risk.
• Ports, ships and offshore platforms.
• Fire services, on tenders and trolleys, for large industrial and tanker fires.

In India’s oil and gas sector, fire protection, including foam systems, follows standards set by the Oil Industry Safety Directorate (OISD). Some OISD standards, such as OISD-STD-116, are mandatory because they are written into statutes like the Petroleum Rules, 2002.

Best practices

• Use the right foam. Different fuels need different foam concentrates. Ordinary foams can break down on alcohols and other water-mixing solvents such as ethanol, which need alcohol-resistant foam. Check what you store against what is in your foam tank.
• Keep enough concentrate. A big tank fire uses a lot of foam. Keep the stock your design requires, check its expiry and quality, and know where more can come from.
• Maintain and test. Check swivels, locks, nozzles, valves and proportioners regularly, and do test runs that confirm the foam is being made at the correct ratio.
• Place them well. Fixed monitors should cover the high-risk areas and be reachable without walking into the fire. Keep access roads clear for tenders and trolleys.
• Train the crew. Operators must know how to set up, aim, adjust and shut down the monitor, how to read the wind and how to avoid foam blowback. They must wear suitable PPE and keep a safe distance.
• Do not break the blanket. Once a foam blanket is in place, avoid hitting it with straight water streams, which can break it and let the fire flare up again.

For everyone else

Foam monitors are tools for trained fire crews. If you see a fuel or chemical fire, do not go near it or try to fight it. Move away, upwind, warn others and call 101 or 112. Tell them what is burning if you know.

Foam monitor working principle, types and upkeep

The outline above covers the basics. Here is what happens between the pump house and the burning tank, the main kinds of monitor, how they are used on ships, and what to check so the monitor works on the day it is needed.

Working principle, step by step

1. Water arrives under pressure. The fire pump, a hydrant main or a tender pushes water into the monitor’s flanged inlet. Monitors are rated at a set nozzle pressure; one maker’s flow tables, for example, are based on 6.89 bar (100 psi).
2. Concentrate is proportioned. Foam concentrate is mixed into the water at a fixed ratio, typically 1%, 3% or 6% by volume, as marked on the drum. The mixing is done either upstream, by a bladder tank, a balanced-pressure foam pump or an in-line inductor, or at the monitor itself by a self-inducing nozzle.
3. Induction pulls the concentrate in. An inductor or eductor uses the venturi effect: water speeding through a narrow throat creates suction that draws concentrate from an unpressurised drum or tank. A self-inducing nozzle works the same way through its own pick-up hose. Back-pressure and a changed hose length upset the ratio, which is why makers say not to shorten or lengthen the pick-up hose.
4. Aspiration turns solution into foam. An air-aspirating nozzle draws air into the foam solution so it expands into bubbles. On ship helidecks, IMO rules require air-aspirating nozzles on any foam monitor of up to 1,000 litres a minute.
5. Throw lays the blanket. The operator sets the pattern from straight jet to fog and the elevation. Maximum reach usually comes at about 32 to 38 degrees. One maker’s chart for a 3,785 litres-a-minute (1,000 US gpm) monitor shows a straight water jet reaching roughly 65 metres in still air. Foam solution, a self-inducing nozzle, a fog pattern and wind all cut that distance, so plan coverage with margin.

Fixed, portable, oscillating and remote-controlled monitors

• Fixed: bolted to a riser at a tank farm, loading rack or jetty and aimed by a tiller or handwheel. Many are part of a deluge or flow-control system, so water reaches them when the valve opens.
• Portable or trailer-mounted: on a trolley, skid or trailer and fed from hydrants or a tender, for risks that move around, such as a tanker spill on a road or at a depot gate.
• Oscillating: a small water turbine, run by a little of the monitor’s own flow, sweeps the stream from side to side over a set arc, adjustable from 15 degrees up to a full circle. It keeps working in places too hot or dangerous for anyone to stand.
• Remote-controlled: electric drives and a joystick let the operator aim the stream and change the pattern from a safe distance or a control room.

Foam monitors on ships and helidecks

Oil and chemical tankers carry a deck foam system, and monitors also protect barges and jetties where cargo is transferred. For a ship’s helideck, the IMO Fire Safety Systems Code (chapter 17, in force from 1 January 2020) asks for at least two fixed foam monitors or deck-integrated foam nozzles, plus at least two foam hose reels. Each monitor must supply at least half the required foam rate and never less than 500 litres a minute. The far edge of the deck must lie within 75% of the monitor’s still-air throw, and there must be enough concentrate to run everything for at least 5 minutes. The same rules want oscillating monitors pre-set to a spray pattern with a quick switch to manual control.

Maintenance checklist

• Every month: check the foam concentrate level and that every valve is in its correct open or shut position.
• Every quarter: open and clean the foam strainers of any sludge or gel.
• Moving parts: grease the swivel joints and gears at the greasing points, and check the monitor turns through its full arc and locks firmly.
• Oscillating monitors: use the test valve to check the sweep and the stops without discharging foam.
• Every year: send a concentrate sample to the maker or a qualified laboratory, and test the proportioning ratio at the nozzle with a refractometer or conductivity meter. A 3% system should read between 3.0% and 3.9%.
• Records: follow the standard your site works to, such as the OISD standards for oil and gas or the maker’s manual, and log every check. While a monitor is out of service, arrange a fire watch for that area.