An area which, for the purpose of the installation and use of electrical equipment, is regarded as dangerous. Such hazardous areas are graded into hazardous zones depending upon the probability of the presence of a flammable gas mixture.

Hazardous energy in occupational safety and health is any source of energy (including electrical, mechanical, thermal, chemical, hydraulic, and pneumatic sources of energy) that "can be hazardous to workers", such as from discharge of stored energy.

Chemicals that are dangerous and likely to harm people health.

Hazardous waste is waste that has substantial or potential threats to public health or the environment.

A HCNG dispenser is a type of fuel dispenser at a filling station that is used to pump HCNG into vehicles.

A manifold that joins parallel loops to a common header pipe.

A liquid storage tank which maintains a head or gravity pressure in the system. It acts as an expansion tank and also supplies liquid to make up for system losses.

Water that is held by a dam and routed to penstock pipes that feed water turbines at a lower elevation.

The health and environmental impact of the coal industry includes issues such as land use, waste management, water and air pollution, caused by the coal mining, processing and the use of its products.

Heap leaching is an industrial mining process used to extract precious metals, copper, uranium, and other compounds from ore using a series of chemical reactions that absorb specific minerals and re-separate them after their division from other earth materials.

A statement, usually in the form of a system diagram, of the heat energy available in a system and the way it is distributed.

In thermal physics and thermodynamics, the heat capacity ratio, also known as the adiabatic index, the ratio of specific heats, or Laplace's coefficient, is the ratio of the heat capacity at constant pressure (CP) to heat capacity at constant volume (CV).

A device which can detect a fire, or a considerable change in temperature, as a result of the action of heat on a sensing element.

Heat is energy in transfer to or from a thermodynamic system, by mechanisms other than thermodynamic work or transfer of matter.

In thermodynamics and engineering, a heat engine is a system that converts heat or thermal energy to mechanical energy, which can then be used to do mechanical work.

A heat exchanger is a system used to transfer heat between two or more fluids.

Heat flux or thermal flux, sometimes also referred to as heat flux density, heat-flow density or heat flow rate intensity is a flow of energy per unit of area per unit of time.

A heat flux sensor is a transducer that generates an electrical signal proportional to the total heat rate applied to the surface of the sensor.

When cooling a building the heat gain is the amount of btu's a system must be able to reject elsewhere.

Heat load is a calculation that identifies both the heat gain and the heat loss.