In thermodynamics, the Helmholtz free energy is a thermodynamic potential that measures the useful work obtainable from a closed thermodynamic system at a constant temperature and volume.

A person who steers the vessel while underway.

Workstation from which the ship can be steered by a helmsman, preferably conceived for working in seated position.

HEPA (high-efficiency particulate air) filter, also known as high-efficiency particulate absorbing filter and high-efficiency particulate arrestance filter, is an efficiency standard of air filter.

Underwater dry stern seal replacement system developed by the Subsea Solutions Alliance.

The hertz (Hz) is the derived unit of frequency in the International System of Units (SI) and is defined as one cycle per second.

Heterogeneous is distinctly nonuniform consisting of dissimilar elements or parts; not homogeneous.

A heuristic technique is any approach to problem solving or self-discovery that employs a practical method that is not guaranteed to be optimal, perfect, or rational, but is nevertheless sufficient for reaching an immediate, short-term goal or approximation.

The HiBuoy is a new mono-buoy concept developed by Hitec Marine AS for mooring and loading of tankers.

Hierarchy of hazard control is a system used in industry to minimize or eliminate exposure to hazards. The hazard controls in the hierarchy are, in order of decreasing effectiveness: Elimination, Substitution, Engineering controls, Administrative controls, Personal protective equipment.

“Don’t wait, activate” they are the instructions given to clients of Marioff new machinery space flooding total fire protection system, HI-FOG MT4. There is no need to evacuate personnel, seal the space or shut off the ventilation.

The water-mist fire-fighting system developed by Finnish company Marioff. The HI-FOG system is based on the removal of harmful smoke and gases produced by a fire, and uses specially-developed sprinkler and spray heads.

A foam compound, which expands during curing to fill voids.

BITFLOWER has been designed to transport molten bitumen, hot pitch, and related products of transportation temperatures up to 250°C. The double-skin hull surrounds two cargo holds with a cargo tank block installed in each of them.

Heat content of the fuel with the heat of vaporization included. The water vapor is assumed to be in a liquid state.

High-level radioactive waste management concerns how radioactive materials created during production of nuclear power and nuclear weapons are dealt with.

High-level waste (HLW) is a type of nuclear waste created by the reprocessing of spent nuclear fuel.

High temperature hydrogen attack, also called hot hydrogen attack or methane reaction, is a problem which concerns steels operating at elevated temperatures (typically above 400 °C) in hydrogen-rich atmospheres.

A device to prevent the passage of flame, consisting of a mechanical valve which adjusts the flow opening in accordance with the pressure at the inlet of the valve in such a way that the efflux velocity cannot be less than 30 m/s.

Varieties of high-viscosity mineral oils that can be found naturally, in oil-sand for example, or can be extracted from the heavy residues from oil refineries.