User's Manual

■ Wind speed to be less than 10 metres / second (19.5 kn.).
As well as temperature, there are other environmental conditions that should also be
taken into account when planning a thermographic building survey. External inspec-
tions, for example, may be influenced by radiation emissions and reflections from
adjacent buildings or a cold clear sky, and even more significantly the heating effect
that the sun may have on surface.
Additionally, where background temperatures differ from air temperatures either inter-
nally or externally by more than 5 K, then background temperatures should be mea-
sured on all effected surfaces to allow surface temperature to be measured with suf-
ficient accuracy.
27.4.8.6 Survey and analysis
The following provides some operational guidance to the thermographic operator.
The survey must collect sufficient thermographic information to demonstrate that all
surfaces have been inspected in order that all thermal anomalies are reported and
evaluated.
Initially, environmental data must be collected, as with any thermographic survey in-
cluding:
■ Internal temperature in the region of the anomaly.
■ External temperature in the region of the anomaly.
■ Emissivity of the surface.
■ Background temperature.
■ Distance from the surface.
By interpolation, determine the threshold temperature to be used.
■ For internal surveys the threshold surface temperature (T
sia
) is T
sia
= f
si
(T
si
– T
so
)
+ T
so
. The thermographer will be looking for evidence of surface temperature below
this threshold.
■ For external surveys the threshold temperature (T
soa
) is T
soa
= f
so
(T
so
– T
si
) + T
si
.
The thermographer will be looking for evidence of surface temperature above this
threshold.
Images of anomalies must be captured in such a way that they are suitable for analysis:
■ The image is square to any features of the wall or roof.
■ The viewing angle is nearly perpendicular to the surface being imaged. Interfering
sources of infrared radiation such as lights, heat emitters, electric conductors, re-
flective elements are minimised.
The method of analysis will depend somewhat on analysis software used, but the key
stages are as follows:
Publ. No. T559597 Rev. a554 – ENGLISH (EN) – September 27, 2011 125
27 – Introduction to building thermography