Phoenix Journal · Ductwork
Fats, oils and grease sit behind roughly three quarters of the UK's sewer blockages - and a web of long-standing law makes their control your responsibility. Here is what the rules actually require of a commercial kitchen.
The last pan is scraped, the fryers are cooling, and somewhere below the floor the day's work is still moving - a slow, warm tide of fat, oil and grease sliding toward a public sewer that was never built to swallow it.
It looks like nothing while it is warm. By the time it reaches the cold brick of the sewer it has set hard, gathering everything that passes into a grey mass that narrows the pipe week by week. Water companies clear roughly 300,000 blockages a year at a cost estimated near £100 million, and the Environment Agency has long put fats, oils and grease at the heart of around three quarters of them. When one of those blockages traces back to your kitchen, the rules stop being abstract very quickly. This is a plain guide to what the law actually asks of a commercial kitchen in England and Wales, and why the quiet discipline of grease management is cheaper than the alternative.
The legal spine
There is no single "FOG Act" to point at. Instead a handful of long-standing statutes overlap, and together they leave a food business with clear duties. Understanding which rule bites when is the difference between a compliant kitchen and one that is quietly exposed.
The blunt end of the law is Section 111 of the Water Industry Act 1991. It makes it a criminal offence to discharge into a public sewer anything that could injure the sewer, interfere with the free flow of its contents, or prejudice its treatment - and congealed grease does all three. You do not need to have set out to cause harm; the discharge itself is enough. A prosecution under Section 111 can reach a fine of up to £50,000 in the Magistrates’ Court, and an unlimited fine in the Crown Court. Just as bruising in practice, the sewerage undertaker can recover the cost of clearing what you caused. When a single notorious fatberg took nine weeks and around £220,000 to remove, it is easy to see why water companies now trace blockages back to source and recharge the businesses responsible.
Above that sits Section 118 of the same Act. If your kitchen discharges trade effluent to the sewer - and a commercial kitchen does - the sewerage company can require consent and set conditions on it: the volume, the temperature, the acidity, and the concentration of oil and grease it will accept. Many consents specify a Total Oil & Grease limit and expect you to provide inspection and sampling facilities so the figure can be checked. Separately, the waste that never reaches the drain is caught by the Environmental Protection Act 1990. Used cooking oil and the contents of your grease trap are classed as controlled waste, which means a registered waste carrier must collect them and you must keep the waste transfer notes for at least two years. The strands pull in the same direction:
From statute to practice
Regulation tends to describe an outcome rather than a shopping list, and that is deliberate - it leaves room for the right solution in a cramped basement kitchen and a purpose-built unit alike. The through-line is simple: keep grease out of the sewer, prove that you are doing so, and dispose of what you capture responsibly.
Approved Document H asks that drainage serving a hot-food kitchen be fitted with a grease separator complying with BS EN 1825, or another equally effective means of grease removal. That standard matters because it is where sizing lives. BS EN 1825-1 covers the design and construction of the separator; BS EN 1825-2 covers how you select the nominal size, either from the type of operation and the meals served or from the grease-producing equipment installed. Get the size wrong and the unit either overflows in service or lulls you into thinking you are protected when you are not. Whichever route you take - a passive separator, a dosed biological system, or an automatic grease recovery unit - the maintenance rhythm is the part people underestimate. The guidance is to empty a trap before it reaches roughly a quarter full of grease, which for a busy kitchen can mean monthly or more often. A device that is never serviced is not grease management; it is a blockage with a warranty.
Compliance is as much about evidence as equipment. If a blockage is investigated, or your trade effluent consent is sampled, the questions come fast: when was the trap last emptied, who carried the waste away, and where is the transfer note. A kitchen that can answer in seconds is in a very different position from one that cannot. It is worth holding these habits together as a single routine rather than a scatter of separate chores:
None of this exists in isolation from the extraction system overhead. The same fat that congeals in a drain is deposited across canopy, filters and ductwork, where it becomes a fire risk rather than a flood one - so the disciplines sit side by side. If you are weighing the true price of getting it wrong, our guide to how fats, oils and grease cost you at the drain puts numbers to the problem, and when you are ready to build the solution properly, how to specify a grease management system walks through sizing and selection step by step. Handled together, the drain and the duct keep your kitchen on the right side of both the Environment Agency and your insurer.
Questions
There is no law that names a grease trap specifically, but the effect is close to it. Approved Document H of the Building Regulations requires drainage serving a hot-food kitchen to be fitted with a grease separator complying with BS EN 1825 or another effective means of grease removal. Combined with the offence under Section 111 of the Water Industry Act 1991 of discharging grease that can block a sewer, that leaves most kitchens needing a properly sized and maintained system in practice.
Under Section 111 of the Water Industry Act 1991, discharging FOG that interferes with the free flow of a sewer is a criminal offence carrying a fine of up to 50,000 pounds in the Magistrates' Court and an unlimited fine in the Crown Court. On top of any fine, the water company can recover the cost of clearing the blockage you caused, which for a large fatberg can run into hundreds of thousands of pounds. Poor record-keeping around waste disposal can bring separate action under the Environmental Protection Act 1990.
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