A Back Pressure
is a pressure that can cause water to Backflow
into the water supply when a user's waste water system is at a higher pressure than the public system.
A Backflow /Back Siphonage
is a reverse flow condition
created by a difference in water pressures that causes water to flow back into the distribution pipes of a drinking water supply
Backflow is a reverse flow in water pipes.
: A background (radiation)
is Natural radiation caused by sun exposure
, cosmic rays from space, and radioactive elements
found in the earth's crust.
A Background concentrations:
is In this context, EPA
uses background concentrations to mean the contributions to outdoor Air Toxics
concentrations resulting from natural sources, persistence in the environment
of past years' emissions
transport from distant sources.
A Background count rate
is the counting rate obtained on a given instrument with a background counting sample
reference background counting samples are:
is the normal extinction of various species as a result of changes
in local Environmental conditions
. Compare mass depletion, mass extinction.