Functional Safety - MEDC DB3 Technical Manual

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7.0 FUNCTIONAL SAFETY

Introduction
The DB3 sounder 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 DB3 sounder 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 a pre-determined audible warning sound when required if the
correct voltage is applied to the unit. The DC version of the sounder is designed to operate on a supply
voltage between 12 and 48vDC; the AC versions of the sounder are designed to operate on a supply voltage
tolerance of +/- 10%.
Under No fault (Normal) Operating conditions the DB3 sounder will provide an audible warning sound when
required by the system.
Under fault conditions the failure mode of the sounder 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
This sounder 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
DC version of DB3 sounder against the requirements of IEC 61508-2 using a Proof Test Interval of 8760hrs.
The DC version of the sounder was considered to be the worst case. The results are shown below and are
based on Route 1
The sounder is classed as a Type B 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 2013
Title:
H
Safety Function of DB3 Sounder:
'To provide a pre-described audible warning sound when required'
DB3 TECHNICAL MANUAL
DB3 SOUNDER
Type B Proof Test
HFT=0 Interval
SFF = =8760Hrs
74.00% MTTR = 8 Hrs
λ
= 3.25E-06
DD
λ
= 2.15E-06
DU
PFD =9.44E-03
AVG
(Low Demand Mode)
PFH = 2.15E-06
(High Demand Mode)
SC 2 (Ref to 56A24816B)
SIL 1 (Low Demand)
SIL 1 (High Demand)
PROCEDURE/
DOCUMENT NO.
DD036-0
SIL 1
[4]
[4]
λ
= 2.20E-08
SD
λ
= 2.81E-06
SU
SIL 2
SIL 1
Route 1
H
Route 1
S
8
-03