HAZOP_GUIDE_BRITISH_STANDARD_IEC_61882_2001

HAZOP_GUIDE_BRITISH_STANDARD_IEC_61882_2001

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Unformatted text preview: with dedicated hard-wired circuit Action by 6 8812 E I2:C100 © BSI 28 August 1002−80 ISB © 2001 Table B.4 ( continued ) BS IEC 61882:2001 43 34 Licensed Copy: Puan Ms. Norhayati, Petroliam Nasional Berhad 4397000, 01 October 2003, Uncontrolled Copy, (c) BSI No. 11 Element Guide word Deviation Possible causes Consequences Safeguards Activities emit alarm and transmit to personnel NO No alarm sounded Sound equipment failure Personnel not alerted Dual PA system Cable damage Dual cabling Comments Actions required None Action by 6 8812 E BS IEC 61882:2001 I2:C100 44 44 Table B.4 ( continued ) Unlikely Dual power supplies Multiple speakers MORE More alarm Sound equipment too powerful Personnel suffer ear damage Sound equipment rated to not exceed safe level None 13 LESS Less alarm Sound too weak Some personnel not alerted None Ensure system provides a minimal of 15 dB above background 14 AS WELL AS As well as alarm and transmit Distortion of alarm, overtones or echoes Lack of clear-cut signal to personnel None Investigate need for acoustic engineering 15 PART OF Part of alarm transmit Alarms but transmission inadequate No signal to personnel 16 REVERSE Reverse alarm and transmit As for less alarm above See comments above reverse initiations and "all clear" – 78 – 12 © BSI 28 August 2001 1002−80 ISB © Licensed Copy: Puan Ms. Norhayati, Petroliam Nasional Berhad 4397000, 01 October 2003, Uncontrolled Copy, (c) BSI No. Element Guide word Deviation Possible causes Consequences Safeguards Comments Actions required 17 OTHER THAN Other than emit GPA alarm and transmit System initiates "PAPA" by mistake Confusion amongst personnel. Some may abandon platform by mistake None Review signal logic so that PAPA can only be sounded after GPA 18 SOONER Alarm and transmit sounded too soon GPA initiated before situation requires this action Unnecessary alarm and disruption of work None Establish clear guidelines for platform personnel 19 LATER Alarm and transmit sounded too late GPA initiation after situation required this action Some personnel may be trapped or forced to use alternative and less desirable route None Action by 6 8812 E I2:C100 © BSI 28 August 1002−80 ISB © 2001 Table B.4 ( continued) Clear guidelines as above – 98 – BS IEC 61882:2001 45 54 BS IEC 61882:2001 6 1882 Ó I EC:2001 B.5 – 47 – Piezo valve control system Licensed Copy: Puan Ms. Norhayati, Petroliam Nasional Berhad 4397000, 01 October 2003, Uncontrolled Copy, (c) BSI The piezo valve control system (see simplified Figure B.3) shows how HAZOP can be applied to a detailed electronic system. A piezo valve is a valve driven by a piezo ceramic. The ceramic element is electrically driven and lengthens itself in the charged state. A charged piezo ceramic closes the valve. A discharged piezo ceramic opens the valve. If the piezo ceramic does not lose or gain charge, the state of the valve is kept. The system sprays a flammable and explosive liquid into a reaction vessel (not shown). The overall system with reactor vessel, pipes, pumps, etc. is part of a separate HAZOP study. Here only the application of a HAZOP study to an electronic unit is shown. The operation of the unit is a two-state process designed to close the valve on demand, “state 1”, and open it on demand, “state 2”. An electrical charge from capacitor C1 is conducted via the transistor T1 to the coupling capacitor C2 and via the power wire to the piezo valve to close it. In this case transistor T2 and the protection transistor T3 are closed (high resistance). Capacitor C2 is discharged by transistor T2 to open the valve. To prevent asymmetric charging of the piezo valve, for example by mechanical or thermal stress, transistor T4 connects the low side to ground. An electrical shield around the twisted wires of the cable prevents electro-magnetic influences from effecting the valve. 46 64 64 © BSI 28 1002−80ISB © 1002−80 ISB August 2001 BS IEC 61882:2001 6 1882 Ó I EC:2001 – 48 – Licensed Copy: Puan Ms. Norhayati, Petroliam Nasional Berhad 4397000, 01 October 2003, Uncontrolled Copy, (c) BSI Control unit AC/DC converter T1 charge Cable C2 D1 Piezo valve Power High D2 Low C1 Shield T2 discharge Ground T3 protection D3 T4 D4 R IEC 455/01 Figure B.3 – Piezo valve control system © BSI ISB © 1002−80 August 1002−8028ISB © 2001 47 74 74 BS IEC 61882:2001 6 1882 Ó I EC:2001 – 49 – Description of state 1: c lose valve Part considered: c able from AC/DC converter and from capacitor C1 via transistor T1, diode D1, capacitor C2 to the power side of the valve and from the ground side of the valve via transistor T4 and resistor R to ground. Licensed Copy: Puan Ms. Norhayati, Petroliam Nasional Berhad 4397000, 01 October 2003, Uncontrolled Copy, (c) BSI Description of state 2: o pen valve Part considered: c able from power side of valve via transistor T3, diode D3 and resistor R to ground. The design intent is as follows. Input Activity Source...
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This note was uploaded on 09/15/2011 for the course ECON 102 taught by Professor Calvin during the Winter '11 term at Oxford Brookes.

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