Glossary

Identification codes for steel drums: 1A1 non-removable (tight) head, 1A2 removable (open) head. An opening over 3 inches makes a drum removable-head by definition.

A dished head whose depth is one quarter of the diameter; standard on many pressure vessels.

Propane vessels are filled to at most 80% of water capacity to leave expansion vapor space.

Petroleum industry density scale; higher API = lighter fluid. Diesel ~36°, heating oil ~32°.

The American Petroleum Institute's Manual of Petroleum Measurement Standards — the chapter set covering vocabulary, tank calibration, manual gauging, temperature correction and quantity calculation.

A pressure vessel built to the ASME Boiler and Pressure Vessel Code — residential propane tanks are ASME vessels.

A tank sited above grade. Not covered by the UST programme, but potentially within the SPCC rule where oil is stored in bulk.

42 US gallons for petroleum — 158.987294928 litres exactly. Not a drum, which is 55 US gallons.

Filled to the absolute geometric top — usually above safe working capacity.

British thermal unit, the energy to heat one pound of water 1°F. Propane carries ~91,500 BTU/gal; heating oil ~138,500.

A cylinder with hemispherical heads — the maximum-volume head shape.

Corrosion control for buried steel using sacrificial anodes or an impressed current, keeping the tank shell electrically protected.

The region of a circle cut off by a chord — the wetted cross-section of a partly filled horizontal cylinder.

The large spherical radius of a dished head's center section — equal to D on standard F&D heads.

Commercial measurement of fuel changing ownership — requires certified meters, not geometric charts.

The reference point a measurement starts from; tank charts use the inside tank bottom.

The fraction of a container's capacity actually occupied, as distinct from its nominal or geometric capacity.

A graduated rod lowered to the tank bottom; the wet line shows liquid depth.

A fixed tube through which a tank is sticked or sampled, keeping the stick path vertical.

Any concave tank end — ellipsoidal, torispherical or hemispherical — that adds volume beyond the cylinder.

A low pocket molded into a tank or tote bottom so it drains completely.

A pipe extending a delivery down to within about a foot of the tank bottom, reducing splash, static and vapour loss during filling.

The fraction of an hour a burner or appliance actually fires. Consumption is the firing rate times the duty cycle, and the duty cycle is what changes most between mild and cold weather.

See 80% rule — the maximum propane fill leaving vapor expansion space.

The capped pipe through which a tank receives delivery; on buried tanks, also the sticking access.

Rainwater fitting that discards the first dirty roof runoff before water enters storage.

A buoyant arm or disc driving a dial — reads level mechanically, typically ±5%.

Vertical distance kept between liquid surface and tank top, especially in open tanks.

The extra depth in a containment structure above the volume of the largest container, reserved for rainfall.

How much volume one inch of depth represents; constant for vertical-walled tanks, varying for round ones.

Gallons per minute, the standard flow-rate unit for fill and drain times.

Observed volume corrected to a 60 °F reference temperature using a volume correction factor.

Height of liquid above a point; 1 ft of water ≈ 0.433 psi. Why overhead tanks make pressure.

The amount by which a day's mean temperature falls below a base, conventionally 65 °F, with negatives set to zero. The standard proxy for space-heating demand.

Unpumpable liquid remaining below the outlet.

Intermediate Bulk Container — caged plastic tote, commonly 275 or 330 gallons.

4.54609 litres exactly, by UK statute. About 1.2 US gallons.

Liquid depth measured up from the tank bottom — what a dip stick reads. The opposite of outage.

The 1959 agreement fixing the yard at exactly 0.9144 m, from which the inch follows as exactly 25.4 mm. Every inch-to-metric volume factor descends from it.

Leak detection in the space between a tank's inner and outer walls, or between a tank and a secondary barrier.

Daily recorded measurements of inputs, withdrawals and remaining stock, reconciled monthly against delivery receipts, to detect a release.

The international standard series for calibrating vertical cylindrical tanks, Part 1 covering the manual strapping method.

Degree days per gallon of fuel burned. Computed from the degree days accumulated between two tank readings divided by the gallons used, it is the number fuel dealers use to schedule automatic deliveries.

The curved transition between a tank shell and a dished head.

The small transition radius between a dished head's crown and the tank shell — 0.06D on standard ASME F&D heads.

One cubic decimetre exactly, per the BIPM SI Brochure. A unit accepted for use with the SI rather than an SI unit itself.

Litres per capita per day — the water-planning unit; IS 1172's norm is 135 lpcd.

A release-detection method in which the tank is left undisturbed for a set period and stick readings at each end are compared against a published threshold. Permitted as the sole method only for smaller tanks.

Bacterial and fungal growth at the fuel–water interface, producing the sludge that blocks filters and lines. It lives on the water, not the fuel.

Gross standard volume with sediment and water deducted — the quantity a barrel of oil is actually traded as.

The US standard for oil-burning equipment installation, including indoor tank placement.

The Liquefied Petroleum Gas Code — source of propane tank clearance distances.

The US legal-metrology reference for weights and measures; its Appendix C tabulates the customary unit chains and fixes the gallon at 231 cubic inches.

The marketing size of a tank (e.g. 55-gal drum), often different from brim-full geometric volume.

The gallons per hour an oil burner's nozzle delivers at rated pressure, stamped on the nozzle. It gives the rate while firing, not consumption.

A cross-section with two flat parallel sides joined by semicircular ends; the shape of standard 275/330 oil tanks.

The flat-sided, semicircular-ended cross-section of standard 275 and 330 heating-oil tanks — 27 inches wide so the tank passes through a 30-inch basement door.

The volume actually gauged in the tank, at whatever temperature it happened to be. The starting point, not the traded quantity.

The distance from a fixed reference point at the top of the tank down to the liquid surface. Used where the tank bottom cannot be reached reliably.

The hazard tier a packaging is approved for, recorded in the UN marking. Group I is the most severe.

The vertical pipe from grade down to a buried tank's opening. Its height must be subtracted from a stick measurement to get liquid depth.

Fraction of rainfall that actually leaves a roof as collectable water; ~0.8 for sloped roofs.

A dike, bund, vault or sump sized to hold the contents of the largest single container plus freeboard for precipitation, so a leak is confined until it can be cleaned up.

The non-product fraction of a gauged parcel, deducted from gross standard volume to reach net standard volume.

Measuring liquid depth (marine usage); same operation as sticking a tank.

Spill Prevention, Control, and Countermeasure — the US rule requiring plans and secondary containment at facilities storing oil above threshold quantities.

Density relative to water; multiplying water weight by SG gives liquid weight.

Industry name for a calibrated depth-to-volume table — what this site calls a tank chart.

A tank's capacity table produced by physical measurement rather than computed geometry, with corrections for plate thickness, shell expansion and tilt.

An underground bulk storage tank filled from intermittent mains, paired with an overhead tank.

A condition — an unexplained water presence, a sudden loss of product, erratic dispensing — that obliges the owner of a regulated tank to report to the implementing agency, normally within 24 hours.

A test capable of detecting a 0.1 gallon-per-hour leak from any part of a tank that routinely holds product, accounting for thermal effects, vapour pockets and the water table.

Deviation of a tank from level, deliberate on many buried installations so product drains to one end. It shifts every depth reading and is corrected for explicitly in calibration standards.

The empty weight of a container; gross minus tare is the liquid weight.

A dished tank end made of a spherical dish and a toroidal knuckle; the common ASME F&D head.

The listing standard for steel underground tanks for flammable and combustible liquids.

The listing standard for steel tanks for oil-burner fuel — the construction standard behind the familiar 275 and 330 gallon aboveground tanks.

The empty space between the liquid surface and the top of the tank.

The moulded or stamped code on a drum or IBC recording its design type, packing group, rated capacity, maximum gross mass and date of manufacture. Authoritative where a trade label is not.

231 cubic inches exactly, by definition in NIST Handbook 44 — the anchor for every US customary volume conversion.

A tank with 10 % or more of its volume below grade. Federally regulated, with a definitional exclusion for heating oil consumed on the premises where stored.

See ullage; in pressure vessels, the gas-filled region above the liquid.

How fast a propane vessel can boil liquid into gas. It depends on the wetted surface inside the tank and the outside temperature, so a small tank at a low level in deep cold can fail to meet demand while still holding liquid.

Device on oil tank vents that whistles during filling and stops near full — the driver's audible gauge.

The multiplier that converts an observed volume to a standard-temperature volume, tabulated in ASTM D1250 / ISO 91 and applied under API MPMS Ch. 11.1.

The layer of water that collects beneath the product, because water is denser than fuel. It corrodes the shell from inside and hosts microbial growth at the interface.

The total volume of a vessel measured in water gallons — how propane tanks are sized.

Measuring the depth of the water bottom, normally with water-finding paste on the gauge stick, so it can be deducted from the total gauged volume.

A paste applied to the bottom of a gauge stick that changes colour on contact with water, marking the water line sharply against the oil above it.

The boundary between wet and dry on a withdrawn gauge stick — the actual measurement.

Usable volume between practical full and the outlet — less than geometric capacity.