User guide

Application Guide | Gas detection in refrigeration systems
© Danfoss | DCS (MWA) | 2018.05 DKRCI.PA.S00.A1.02 | 520H12772 9
Requirements for gas detection
according to EN 378:2016 and
ISO 5149:2014
With a few exceptions gas detection is required
by EN 378:2016 and ISO 5149:2014 for all
installations where the concentration in a room
may exceed the practical limit for that space.
In the case of flammable and toxic refrigerants
this means virtually all commercial and industrial
systems In the case of A1 refrigerants it is possible
to have small systems, which do not require gas
detection. However, in most of the larger plants
it is likely that the practical limit will be exceeded
in the event of a major leak, and therefore gas
detection is required.
Guidance can be found in EN 378:2016 part
3 or ISO 5149:2014 part 3. The requirements
of the two standards are very similar, and are
summarised in fig. 5.
If it can be shown by calculation that the
concentration of refrigerant in a room can never
reach the practical limit; then there is no need for
fixed gas detection, except according to EN 378 if
the system is below ground with a charge above
m
2
(approx. 1 kg of propane). ISO 5149 does not
have this exception. m
2
is a constant equal to
26m
3
x LFL. For propane it is 26 m
3
x 0,038 kg/m
3
= 0,988 kg, or, if your LFL is measured in gram, it is
26 m
3
x 38g/m
3
=988 g. As such m
2
does not have
any units, since the units depend solely on which
unit you chose for LFL.
Most hydrocarbons have similar value of LFL, and
m
2
is therefore typically around 1kg.
However, if the concentration can reach the
practical limit, even for A1 refrigerants, then fixed
detection must be installed - again with a few
minor exceptions.
The practical limits for various refrigerants are
given in Annex II, which are extracted from EN
378-2016 part 1. In these tables the practical
limit of ammonia is based upon its toxicity. The
practical limits of the hydrocarbons are based
upon their flammability and are set at 20% of
their lower flammable limit. The practical limits
for all the A1 refrigerants are set at their Acute
Toxicity Exposure Limit (ATEL).
If the total refrigerant charge in a room, divided
by the net room volume, is greater than the
“practical limit” (see Annex II), it is reasonable to
conclude that fixed gas detection system should
be installed.
Both EN378:2016 and ISO 5149:2014 require that
an indicating device is provided to show whether
the relief valve has discharged on systems with
300 kg refrigerants or more. A possibility is to
place a gas detector in the discharge line.
Fig. 5: Requirements for gas detection according to EN 378:2016 part 3 and ISO 5149:2014 part 3
Y
N
N
Y
Y
Y
N
Y
Y
N
Charge >
50 kg
Gas detector
required
Ammonia
Start
Gas detection
required
high/low level
N
Gas detector
used to start fan or
close valves
Charge >
100% practical
limit
N
Y
Gas detector
required
N
Using EN 378
and charge >m
2
and A3 or B3
Below ground
in machinery room
or open air
Y
No requirements
N
Charge limits
for ventilated
enclosure
Charge limits
using alternative risk
management