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8.0 FUNCTIONAL SAFETY
Introduction
The XB15 Beacon 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 safety function of the Beacon is to provide an intermittent spherical visual warning light when
the correct voltage is applied to the unit. The DC versions of the Beacon are designed to operate on
a supply voltage tolerance of +/- 20%; the AC versions of the beacon are designed to operate on a
supply voltage tolerance of +/- 10%.
The telephone initiate versions of the Beacon are not included in this safety manual.
Under No fault (Normal) Operating conditions the XB15 Beacon will provide a spherical visual
warning light when required by the system.
Under fault conditions the failure mode of the Beacon is a failure to provide a spherical visual
warning light. For the failure rate associated with this failure mode please refer to the table below.
Assessment of Functional Safety – XB15 DC
This Beacon 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 XB15 Xenon Beacon against the requirements of IEC 61508-2 using
a Proof Test Interval of 730hrs.
The results are shown below and are based on Route 1H.
The Beacon is classed as a Type B device.
Safety Function:
'To provide a spherical cycled visual warning light when energized'.
Summary of Clauses
2/7.4.2 and 2/7.4.4
Architectural constraints
Safe Failure Fraction (SFF)
Random hardware
-1
failures: [h
]
Random hardware
-1
failures: [h
]
Diagnostic coverage (DC)
PFD @ PTI = 730Hrs, MTTR = 8 Hrs
Average freq. of dangerous failure (high
-1
demand-PFH)[h
]
Hardware safety integrity compliance
Systematic safety integrity compliance
Systematic Capability
(SC1, SC2, SC3, SC4)
Hardware safety integrity achieved
© MEDC 2016
XB15 Xenon Beacon
Single Mode (1oo1)
HFT=0
62%
0.00E+00
DD
5.85E-06
DU
0.00E+00
SD
9.53E-06
SU
0.00%
2.18E-03
5.85E-06
[
Limited to: SIL 1 (1oo1) & SIL 2 (1oo2) due to SFF value.
XB15 DC Beacon
XB15 Xenon Beacon
Redundant Mode (1oo2)
HFT=1
62%
0.00E+00
5.85E-07
0.00E+00
9.53E-07
0.00%
2.18E-04
5.85E-07
Route 1
H
See report R56A24816B
SC2 (R56A24816B)
Verdict
Type B
SIL 1
SIL 2 (1oo1)
SIL 1 (1oo1)
03/16
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