Functional Safety - MEDC DB4 Manuel Technique

7.0 FUNCTIONAL SAFETY

Introduction
The DB4 Speaker has been designed for use in potentially explosive atmospheres and harsh environmental
conditions. The glass reinforced polyester enclosures are suitable for use offshore or onshore, where light weight
combined with corrosion resistance is required.
The DB4 Speaker can be configured with or without an Exe Chamber on the rear.
The FMEDA has considered the worst case scenario which includes the Exe Chamber on the rear.
The safety function of the Sounder is to provide an audible warning when required.
Under No fault (Normal) Operating conditions the DB4 Speaker will provide an audible warning when required.
Under fault conditions the failure mode of the Speaker is a failure to provide an audible warning sound. For the
failure rate associated with this failure mode please refer to the table below.
Assessment of Functional Safety
The DB4 Speaker 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 DB4
Speaker unit against the requirements of IEC61508-2 using a proof test interval of 8760hrs.
The DB4 Speaker is classed as a Type A device.
Architectural constraints:
Random hardware failures:
Probability of failure on demand:
Probability of Dangerous failure on safety function:
Hardware safety integrity compliance
Systematic safety integrity compliance
Systematic Capability
Overall SIL-capability achieved
© Cooper MEDC 2011
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Proven in Use Summary Table
DB4 SPEAKER
Safety Function of the DB4 Speaker:
To provide an audible warning sound when required'
Type A
HFT=0
SFF = 85.00%
!
!
PFD
(Low Demand Mode)
PFH = 4.70E-07
(High Demand Mode)
Proof Test Interval
=8760Hrs
MTTR = 8 Hrs
= 0
DD
= 4.70E-07
DU
=2.06E-03
AVG
Route 1
Route 1
SC2
SIL 2 (Low Demand)
SIL 2 (High Demand)
SIL2
!
= 0
SD
!
= 2.86E-06
SU
SIL2
SIL2
H
S
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