Hazardous Area Operation
Hazardous Area
– General
Thermo Fisher Scientific
Prima PRO & Sentinel PRO Mass Spectrometers User Guide
A-5
categorises the gases that may be present in hazardous
areas.
Table A
–2.
Gas classification
Typical Gas*
Europe
North America
Propane / methane
Group II A
Class 1, Group D
Ethylene
Group II B
Class 1, Group C
Hydrogen
Group II C
Class 1, Group B
Acetylene
Group II C
Class 1, Group A
*Refer to the appropriate standard for a full listing of the gases in each group.
Most methods of protection rely on removing the source of ignition or
separating it from the flammable gas. Hot surfaces represent a
potential source of ignition and surface temperatures are classified as
in
Table A
–3.
Surface temperature classification
Maximum Surface Temperature
T Class
450°C
T1
300°C
T2
200°C
T3
135°C
T4
100°C
T5
85°C
T6
The T class for electrical apparatus represents the maximum surface
temperature that can occur in normal operation or, if appropriate, a
fault condition, and is normally determined as part of the
certification process. A given hazardous area will have a
specification for the T class for apparatus allowed to be used in that
area.
There are a number of methods of protection used to protect against
ignition of flammable gases by sparks. Only those relevant to the
Prima PRO Ex and Sentinel PRO Ex are considered here.
This method allows a safe area electrical apparatus to be used in a
hazardous area by placing that apparatus in an enclosure pressurised
with clean air or an inert gas. The positive pressure in the enclosure
ensures that any flammable gas external to the enclosure cannot enter
the enclosure and be ignited by sparks, hot surfaces, etc. Depending
on the area classification, it may be necessary to interlock the
enclosure power to the enclosure pressure, i.e. if the pressure falls,
the power will be switched off.
Gas
Classification
Methods of
Protection
Purge /
Pressurisation
