Glossary

air terminals – lightning rods, strike termination devices
Conductor rods offering an air connector for lightning to strike. Positive streamers emit themselves from system of copper or aluminum lightning rods strategically sited on a structure so they can intercept lightning strikes before they hit the building they are protecting.
average ground flash density
The number of strikes for a given area of land
BSCP
British Standard Code of Practice.
BS & EN
British and European Union Standards.
blue jets
Blue tinted flashes of high altitude lightning occurring above a thunderstorm.
bonding conductors – downleads, down conductors
Metal conductors connecting parts of a lightning protection system together and to the ground. Bonding conductors not only have to have low resistance, but also low self-inductance (resistance created by passing electric currents and magnetic fields)
bosun’s chair – boatswain’s chair
An apparatus with a rigid seat used to suspend a person from rope(s) to carryout work or for transportation.
connecting leader
See positive streamer
cone of protection
An area of increased safety from lightning provided by the highest point of a lightning protection system on a structure.
coulomb
1 coulomb is the amount of electric charge transported in one second by a steady current of one ampere.
1C = 1A x 1s
1 Coulomb is also the amount of charge stored by 1 farad of capacitance to a potential difference of one volt.
1C = 1A x 1v
cumulonimbus
Latin for “column rain”, Cumulonimbus is the type of cloud involved in thunderstorms, lightning and other intense weather. They are tall, dense and the result of atmospheric instability.
dart leader
A charged path of ionized air already created and used by primary lightning strike.
downleads
See bonding conductors
down conductors
See bonding conductors
faraday cage
A safe enclosure formed by conductive material designed to redistribute the electrical energy so canceling its effects to the interior of the cage and protecting its contents.
flashovers
The act of lightning jumping from one conductive path to another.
heat lightning
Lightning that is so far away its thunder is not heard or associated with the lightning flash. Over 10 miles the sound of thunder is faint and takes over 45 seconds to reach you. This type of lightning occurs in the heat of summer when the sky overhead is clear, hence why it is call “heat lightning”
high altitude lightning
Lightning that occurs above a thunderstorm cloud.

hydrometeor
Condensation or precipitation of moisture within the Earth’s atmosphere. It is any particle removed from the Earth’s surface by wind into the air.

intra-cloud
The most common form of lightning. It travels internally across storm clouds with differently charged regions. The light created from this type of lightning is commonly referred to as sheet lightning and can be seen from many miles as it flickers internally across the cloud making it glow from inside.

inter-cloud
Rarer than intra-cloud lightning, this form of lightning travels across open air between clouds containing differently charged regions. This form of lightning is dangerous to aircraft trying to avoid thunder storms.
ionisation – ionization
When air gases are turned into plasma, the fourth state of matter. A high negative electrical field accelerates ions present in gas and causes them to collide with other gas molecules. These collisions cause negative electrons to be knocked off the gas molecules creating more positive ions in chain reaction as the positive ions are attracted towards the negatively charge field.
LEMP
Lightning ElectroMagnetic Pulse
lightning leader
See stepped leader.
lightning protection system – LPS
A lightning protection system is a network of conductors and circuits designed to offer protection from lightning strikes to buildings and structures. A lightning protection system offers the electrical charge from a strike a safe path of least resistance to ground.
LPS
see Lightning Protection System
plasma
Broken down or ionised air where electrons are striped from atoms in molecules of air. Plasma is the fourth state of matter, as in solid, liquid, gas and plasma. Plasma is considered a good conductor of electricity when compared to normal air.
positive leader
See positive streamer
positive streamer – connecting leader, positive leader
Positive discharge that normally reaches up from the ground to join a negative step leader originating from a storm cloud
red sprites
Red tinted flashes of high altitude lightning above a thunderstorm.
scaffolding
A temporary structure providing access and elevated platforms on which work can be carried out. The platforms can be used to hold workers and the materials used in the construction, repair and demolition of tall buildings or structures. Normally modular in design for easier construction and transportation using metal pipes or tubes and wooden planks for walkways and platforms. Some countries continue to use wooden or bamboo shafts in the construction of scaffolding.
st. elmo’s fire
A blue greenish glow that occurs above objects with a strong electrical charge during a storm. It is created by the positive charge in the earth’s surface causing tiny streamers to reach up to the negative field of a storm cloud.
The glow appears during thunder storms on tall objects like a ships masts and was thought to be protection given to ships by St Elmo, the patron saint of sailors. In reality St Elmo indicates the possibility of an imminent lightning strike, however, the name probably exists due to only surviving ships being able to spread their beliefs as to what it was.
stepped leader – lightning leader
Paths of negatively charged air with less electrical resistance due it being ionized.
updrafts
Rapidly rising warm air