MEDC BG User Manual
Page 5
© Cooper MEDC 2013
06/13
T
The safety function of the Call Point is to raise the alarm when the Glass is Broken
Under No fault (Normal) Operating conditions the BG Break Glass Unit will raise the
alarm upon operating the switch via breaking the glass.
Under fault conditions the failure mode of the Break Glass is a failure to raise the alarm.
For the failure rate associated with this failure mode please refer to the table below.
Assessment of Functional Safety
The BG Call Point is intended for use in a safety system conforming to the requirements
of IEC61508.
Sira Test & certification Ltd has conducted a Failure Modes Effect and Diagnostic
Analysis (FMEDA) of the BG Break Glass unit against the requirements of IEC61508-2
using a proof test interval of 8760hrs.
The Call Point is classed as a Type A device.
BGI BREAKGLASS UNIT
Safety Function of BG Break Glass Unit:
‘To raise the alarm upon breaking the glass’
Architectural constraints:
Type A
HFT=0
SFF= 97%
Proof Test Interval
=8760Hrs
MTTR = 8 Hrs
SIL3
Random hardware failures:
!
DD
= 0
!
DU
= 5.72E-07
!
SD
= 0
!
SU
= 2.04E-05
Probability of failure on demand:
PFD
AVG
=2.51E-03
(Low Demand
Mode)
SIL2
Probability of Dangerous failure on
safety function:
PFH = 5.72E-07
(High Demand
Mode)
SIL2
Hardware safety integrity
compliance
[1]
Route 1
H
Systematic safety integrity
compliance
Route 1
S
Systematic Capability
SC2
Overall SIL-capability achieved
SIL 2 (Low Demand)
SIL 2 (High Demand)
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