SOLAS Plumbing cheat sheet

Hierarchy of control, most to least effective: eliminate, substitute, engineering controls, administrative controls, PPE. PPE is the last line of defence and never a substitute for removing the hazard.

COSHH requires a current safety data sheet and a documented risk assessment before any hazardous substance (flux, solvent cement, descaler, lead solder, two-pack sealant) is used or stored on site.

Confined-space entry (tanks, pits, sewers, plant rooms with restricted egress) requires a permit, atmospheric testing for oxygen (19.5-23.5% v/v), flammable and toxic gas, a rescue plan and a top-man.

Manual handling assessment uses the guideline figures: load close to the body, avoid twisting, keep lifts below shoulder height, and treat loads over 25 kg as requiring a team lift or mechanical aid.

Working at height hierarchy: avoid work at height, prevent falls using a suitable platform, then mitigate the distance and consequences of a fall. Ladders are for low-risk, short-duration work only.

Hot work (soldering, brazing, grinding) requires a hot-work permit, a fire watch during and for at least 60 minutes after work, and removal of combustibles within the immediate area.

Electrical safety on site: 110 V centre-tapped-to-earth reduced low voltage for portable tools, RCD protection at 30 mA, and PAT testing records available for inspection.

Legionella risk from aerosols means showers, cooling towers, spa pools and stagnant pipework are assessed under the site's water safety plan; report any positive result immediately.

Pressure at a depth: p = rho x g x h. Water at 1 m depth gives about 9.81 kPa, so roughly 10 m head equals 1 bar (100 kPa).

Flow rate through an orifice or terminal fitting: Q = v x A. Doubling the pipe diameter quadruples the cross-sectional area and so quadruples flow at the same velocity.

Bernoulli's equation: p1 + 0.5 rho v1^2 + rho g h1 = p2 + 0.5 rho v2^2 + rho g h2, plus friction losses. Higher velocity means lower static pressure at that point.

Darcy-Weisbach head loss: hf = f (L/D)(v^2/2g). Friction loss rises with length and with the square of velocity, so oversized flow in undersized pipe is the common fault.

Thermal expansion of water: about 4% volume increase from 10 to 100 degrees C; sealed systems need an expansion vessel or a relief valve to accommodate it.

Specific heat capacity of water is 4.18 kJ/kg.K. Heating 1 kg of water by 1 K takes 4.18 kJ, so energy = mass x 4.18 x temperature rise.

Sensible heat and latent heat: raising water from 0 to 100 degrees C takes 419 kJ/kg, and changing 100 degree water to steam at the same temperature takes a further 2257 kJ/kg.

Water hammer is caused by sudden velocity change; mitigation is slow-closing valves, correctly sized pipe, air vessels or surge arrestors, and adequate pipe clipping.

Copper tube is graded by wall thickness: R250 (light), R220 (medium), R200 (heavy). Table X (R250) suits surface-run domestic work; buried or high-pressure work needs heavier grades.

Copper to copper joints are made with lead-free solder and a flux matched to the filler; a nitrogen purge prevents internal oxide scale on medical and high-purity work.

Plastic pipe pressure ratings fall with temperature. A pipe rated PN10 at 20 degrees C is derated at 60-70 degrees C, so check the manufacturer's pressure-temperature table before use on hot water.

PEX and PEX-Al-PEX are joined with press or compression fittings specific to the system; mixing barrier and non-barrier pipe in a heating circuit causes oxygen ingress and corrosion.

Push-fit plastic systems rely on an O-ring seal and a grab ring; the pipe must be cut square, deburred, marked to insertion depth and secured with the correct insert for the pipe type.

Galvanised steel must not follow copper in the direction of flow, because copper ions accelerate galvanic corrosion of the zinc; use a dielectric union at any transition.

Dissimilar metals need isolation: brass and copper are close on the galvanic series and acceptable, but steel with copper or stainless with carbon steel needs a dielectric coupling.

Pipe support spacing depends on material and temperature: plastic pipe needs more clips than copper because its stiffness falls and expansion is greater; follow the manufacturer's spacing table.

Category 5 fluid risk (faecal, animal or human waste) requires an air gap (type AA or AB); reduced-pressure zone valves (type BA) are the minimum for category 4.

Cold water storage cistern sizing: allow at least 100-200 litres per dwelling and 45 litres per occupant per day as a working figure; the cistern must hold a minimum 24-hour supply where the mains can be interrupted.

Cistern installation rules: a screened warning pipe, a lid, an insect screen, a raised base, insulation, and a minimum 150 mm air gap between the float-operated valve outlet and the spillover level.

The water bylaws/regulations require a minimum 15 mm service pipe for a single dwelling and a maximum length of 30 m for a 15 mm pipe from the communication pipe to the stop valve without a pressure check.

Static pressure in a building is set by the height of the highest outlet above the supply; a break tank and booster set are needed when the mains cannot deliver the required pressure and flow.

Balanced cold and hot supplies to a mixer tap or shower prevent pressure fluctuation and temperature swing; unbalanced supplies cause the blended temperature to drift.

Pipe sizing uses the loading-unit method: each outlet has a loading unit, the total is converted to a design flow, and the pipe is sized so velocity stays below about 1.5 m/s in cold and 1.0 m/s in hot services.

Water meters and stop valves must be accessible, and the internal stop valve must be fitted immediately after the rising main enters the building, with a drain cock on the lowest point.

WC flush volumes: 6/4 litre dual flush is the common maximum for new installations; reduced flush must not exceed two-thirds of the full flush.

Trap seal depth must be 75 mm for WC pans and 38-75 mm for other appliances; a seal below 38 mm risks sewer gas ingress and above 75 mm risks self-siphoning.

A branch discharging into a stack must be within 450 mm of the trap outlet (or the trap must be ventilated) to avoid induced siphonage on the appliance.

Washbasin and sink taps are fitted with an air gap or a check valve on any flexible hose connection; a hand-held shower on a flexible hose is a category 5 risk and needs backflow protection.

Bath and shower mixers must limit hot water delivery to 48 degrees C at the outlet for domestic baths and 41 degrees C for showers in healthcare and vulnerable settings.

Accessible WC compartments require a minimum 800 mm clear transfer space beside the pan, grab rails, and a 480 mm high seat in an accessible/ambulant cubicle.

Unvented hot water cylinders and combination boilers must have a temperature and pressure relief valve piped to a safe discharge point, not to a gully inside the building.

Sanitary appliance waste pipes must fall at 18-90 mm per metre for 32-50 mm pipe and 22 mm per metre for a 110 mm branch to maintain self-cleansing velocity.

Self-cleansing velocity in drains is about 0.7 m/s at design flow; below this solids settle, above about 3 m/s scour of the pipe wall occurs.

Soil and waste stack sizing: a 100 mm stack serves up to about 20 WC pans on a domestic system; a 75 mm stack serves up to 6; a 50 mm stack serves up to 2.

Stack ventilation: a vent pipe must rise at least 900 mm above the highest branch and terminate at least 900 mm above any opening window or 3 m horizontally from it.

A stub stack is permitted where the stack carries no more than 6 WC pans and the lowest branch is within 6 m of the drain invert; otherwise a full vent is needed.

Drain gradients in the regulations: 1 in 40 to 1 in 80 for 100 mm pipe, 1 in 40 to 1 in 110 for 150 mm pipe; flatter than 1 in 110 causes solids deposition.

Inspection chambers are required at every change of direction, at junctions of drains, and at intervals of no more than 45 m on a straight run.

A gully trap must be fitted with a sealed grating and its seal must be at least 75 mm deep; rainwater and surface water must not discharge into the foul drain.

Air admittance valves admit air to balance pressure but do not vent foul air; they must be fitted above the flood level of the highest appliance and be accessible for maintenance.

Boiler sizing uses the heat loss of the building, not the radiator count; a room-by-room heat loss calculation is the basis for radiator sizing and flow temperature choice.

Radiator output falls as the mean water temperature falls: a radiator rated at 75/65/20 degrees C (delta T 50) delivers about 75% of that output at 55/45/20 (delta T 30).

Weather compensation lowers the flow temperature as the outside temperature rises, improving condensing boiler efficiency and reducing cycling; the boiler must condense below about 55 degrees C return.

A heat pump needs a low flow temperature (35-45 degrees C) and a well-insulated building; the seasonal performance factor depends on the temperature lift, so oversized emitters matter.

Unvented cylinders need a 3 bar pressure reducing valve, a 6 bar expansion relief valve, a 7 bar temperature and pressure relief valve, and an expansion vessel sized to the cylinder volume.

Solar thermal and heat pump cylinders need a larger coil or a plate heat exchanger to transfer heat at low flow temperatures; a standard indirect coil is often inadequate.

Legionella control in hot water: store at 60 degrees C or above, distribute at 50 degrees C or above, and deliver at the outlet within 1 minute at 55 degrees C (healthcare) or 50 degrees C (other premises).

Underfloor heating manifolds need a mixing valve or a separate low-temperature circuit, a flow meter per loop, and actuators controlled by room thermostats or zone valves.

Backflow protection is selected by fluid category: category 1 wholesome water, 2 slight health hazard, 3 moderate, 4 significant, 5 severe. The protection device must match the highest category downstream.

Air gap (type AA/AB) is the only protection for category 5. Type BA (reduced pressure zone) suits category 4. Type CA (double check valve) suits category 3. Type EA/EB (single check) suits category 2.

Legionella bacteria multiply between 20 and 45 degrees C, with the highest growth around 37 degrees C; above 60 degrees C they die within minutes, and below 20 degrees C they are dormant.

A water safety plan or legionella risk assessment is required for every premises with a water system; it must be reviewed at least every 2 years or when the system changes.

Sentinel outlets are the nearest and furthest from the supply, plus any low-use outlet; they are the first to be sampled and the first to be flushed during a control programme.

Water softeners use ion exchange to swap calcium and magnesium for sodium; they reduce scale but raise sodium content, so softened water must not be used for drinking or infant formula unless a hard-water tap is provided.

Chemical dosing for closed heating systems uses inhibitor at the manufacturer's concentration, typically checked by a test kit for pH (8-10), inhibitor level, and chloride; a corrosion coupon or test kit confirms the result.

TMV (thermostatic mixing valve) type 3 is used for vulnerable persons and must be fitted with a means of temperature verification and a failsafe to shut off hot water on cold failure.

Pressure testing of pipework: test at 1.5 times the design pressure or the manufacturer's figure, hold for at least 1 hour for plastic and 30 minutes for metal, with a visible gauge and a recorded result.

Flushing and chlorination of new mains and storage: chlorinate to 50 mg/l free chlorine for 1 hour contact, then flush until the residual falls below the wholesome water limit.

Commissioning a heating system: fill, vent, cold-flush, dose with inhibitor, set the bypass, balance the radiators to a 10-11 degrees C differential, and record the boiler combustion readings.

Handover documentation must include the benchmark/commissioning checklist, as-installed drawings, O&M manuals, guarantee certificates, and the user instructions for controls.

Gas work handover requires the benchmark log, a warning notice where a defect is found, and a gas safety record for rented property; only a Gas Safe registered engineer may work on gas.

Electrical work on boilers and controls must comply with Part P; minor works and new circuits need certification, and the boiler must be on a fused spur with a 3 A fuse.

Pipe insulation thickness is set by the pipe diameter and location; a 15 mm domestic hot pipe needs at least 9 mm in a heated space and 13-25 mm in unheated or cold spaces to avoid condensation and freezing.

Labelling of pipework is required for isolation valves, drain cocks, and pipes carrying water for non-potable uses; the label must state the fluid and the hazard.

A combi boiler losing pressure repeatedly usually has a failed expansion vessel, a leaking pressure relief valve, or a system leak; isolate the boiler to distinguish a vessel fault from a system leak.

No hot water from a combi with heating working points to a stuck diverter valve, a faulty flow sensor, or a blocked plate heat exchanger; check the flow switch signal before replacing parts.

Radiators cold at the top indicate air, cold at the bottom indicate sludge; a cold radiator at the top with a hot flow pipe suggests a balancing or pump problem.

A WC that runs continuously usually has a worn inlet valve washer, a mis-set float, or a faulty fill valve; a WC that leaks at the base has a failed pan connector or a cracked pan.

A trap that gurgles or empties indicates induced siphonage or a blocked vent; check the branch distance to the stack and the vent terminal before altering the trap.

A water meter turning with all outlets closed indicates a leak on the supply; isolate sections in turn to localise it, and check the ball valve in the cistern first.

Frost damage: a frozen pipe must be thawed from the outlet end towards the supply with warm air or a hot pack, never with an open flame, and the pipe must be checked for splits before restoring pressure.

A boiler lockout with a fault code should be read against the manufacturer's fault table before resetting; repeated resets without diagnosis can flood the combustion chamber with unburnt gas.