H-I-J-K-L

بدضعیفمتوسطخوبعالی (بدون رتبه)
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H

Halogen:
The collective term used to describe the five non-metallic elements…

* Astatine
* Bromine
* Chlorine
* Fluorine
* Iodine

Halogenated Hydrocarbons
A group of chemicals, including some refrigerant gases. Many arise as unwanted by-products such as from the manufacture of pesticides and the incineration of polychlorinated biphenyl (PCB). Some are exceptionally hazardous.

Hyperbaric
A term to be treated with care because it has a multitude of meanings. The standard dictionary definition simply means a pressure greater than normal. In tunnelling it means that the atmospheric environment of the tunnel is elevated to a pressure that allows personnel to work comfortably inside the tunnel, but is high enough to prevent the ingress of water etc. In medicine it means an ultra-high pressure, typically pressurised oxygen chambers that people sit inside for medical treatment.

I

I.B.V:
Inlet butterfly valve. These are fitted on the inlet of most types of compressor and the valve opens and closes to throttle the air flow. However, the term IBV is usually associated with turbo compressors.

I.G.V’s:
See Guide Vanes (inlet).

Inlet Pressure:
This is usually measured at the inlet to the compressor and will not include any losses due to the efficiency of the air intake filter unless otherwise stated.

Inter-cooling:
A multi-stage compressor will have separate coolers between each stage of compression. These inter-coolers attempt to reduce the temperature of the compressed air as low as possible prior to the next stage of compression. This increases efficiency, and also unfortunately the cost of the compressor.

K

Kg
The constant for gaseous explosions. This is measured in bar metres/sec. It is defined as the rate of change, that is pressure/time, multiplied by the volume of the container to the power of 0.333. Also true for Kst. See zone.

Kst
The constant for dust explosions. The ‘st’ stands for STAUB which is German for dust. This is measured in bar metres/sec. Unlike the classification for gases, the explosion classes are in reverse order with ST 0 having no possibility of explosion, and ST 3 being explosive. See zone.

Kyoto Protocol
Signatories to the United Nations Framework Convention on Climate Change met at Kyoto, Japan in 1997. The resulting treaty was later termed the Koyoto Protocol. The US proposed a scheme to rank greenhouse gases according to their level of destructiveness.

i.e. CO2 = 1. Methane = 11, each called the Global Warming Potential. The treaty committed the industrialised countries to reduce emissions of six gases by an average of 5.2% by the year 2012. The treaty also allowed countries to bank or borrow credits in respect of carbon emissions.

L

L/sec ANR:
Volume flow rate measured in litres per second related back to ANR conditions.

Leq – Equivalent noise level:
This is the sound level, averaged over an 8 hour day – that would be equivalent to the effects of a varying sound level that a person would be exposed to, over an 8 hour period.

Lower Explosive Limit (LEL):
Also called the Lower Flammable Limit. Flammable gas or vapour will only burn in air over a limited range of concentrations. If the mixture is too ‘lean’ to burn it is below the lower explosive limit. Also see Upper Explosive Limit.

Lower Flammable (LEL):
See above.

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