Computer HAZOP

As shown in Fig. V/3.5.1 -1, these are actually somewhat similar to computer HAZOP, and mainly used for PEs as discussed in Clause 3.4.5 previously. 

There has been much discussion on the apphcation of HAZOPs to computer-controlled systems (computer HAZOPs or CHAZOPs) 43 particular, defence standard DEF STAN 00-56 calls for HAZOPs in relation to both systems and sub-systems, but the only guide it was able to refer to originally was that for chemical process plant. This omission has now been remedied by the formulation and pubhcation of interim defence standard DEF STAN 00-58 Hazop studies on systems containing programmable electronics. ... 

For computer-controlled plant, it is also recommended that at least one Chazop or computer Hazop is carried out. This addresses the hazard potential of the software (and computer hardware) itself. As with the Hazop, the Chazop may also need to be revisited as a result of changes required during commissioning. 

The hazard study must look for potential hazards in the EUC operating with its basic process control system (BPCS). Generally, control system failures are seen as human operator errors, loop control faults or sequencing/interlock failures. However, it is also necessary for the hazard study to consider possible failure modes of any computer/PLC systems used in the BPCS or in supervisory control. This type of study falls within the scope of what are known as computer hazops or chazops . Section 3.13.3 contains some introductory notes on chazops. 

Computer tools are available to aid information capture. In some cases, tbe facilitator may use tbe computer tool for recording, replacing tbe secretaiy. For example, PrimaTecb offers a veiy useful computer program to aid in HAZOP studies (HAZOP-PC, 1994). Other excellent computer aids for HAZOP are also commercially available. 

The team should have a wide range of knowledge and experience. If a contractor designs the plant, then the HAZOP team should include people from both tlie contractor and client organizations. On a computer-controlled batch plant, the software engineer should be a member of the HAZOP team, which should include at least one other person who understands the computer logic. 

The HAZOP session is recorded on a personal (laptop or desktop) computer by the person assigned to be the recorder. A program for this purpose maybe HAZSEC available from Technica. 1 his record is not a verbatim transcript it is a recording of intermediate or final results as directed h> ihc team leader. 

As described, each session of the HAZOP team is recorded using a computer and special aiftwarc These records are revised whenever open items are resolved to produce the final record. 

The advantage of HAZOP is the combination of the experiences of people from different disciplines which make the study very effective. Also, it enforces a certain discipline to minimize the possibility of overlooking any hazards.Several computer programs to assist in HAZOP studies are available [259,260]. 

Many companies offer computer tools to help facilitate and document HAZOP studies. 

A fundamental objective of a computer system applied to automate a pharmaceutical GMP operation is to ensure the quality attributes of the drug product are upheld throughout the manufacturing process. It is therefore important that quality-critical parameters are determined and approved early in the validation life cycle. The exercise should be undertaken to a written procedure with base information from the master product/production record file examined and quality-critical parameter values and limits documented and approved for the process and its operation. In addition, the process and instrument diagrams (P IDs) should be reviewed to confirm the measurement and control components that have a direct impact on the quality-critical parameters and data. This exercise should be carried out by an assessment team made up of user representatives with detailed knowledge of both the computer system application and process, and with responsibility for product quality, system operational use, maintenance, and project implementation. This exercise may be conducted as part of an initial hazard and operability study (HAZOP) and needs to confirm the quality-related critical parameters for use in (or referenced by) the computer control system URS. 

ASME CFSTR CFD CFM DIERS exp IR HA/AN HAZOP MM MMM American Society of Mechanical Engineers Continuous flow stirred tank reactor Computational fluid dynamics Computational fluid mixing Design Institute for Emergency Relief Systems exponential Infrared (spectroscopy) Hazard analysis Hazard and operability studies Michaelis-Menten Maximum-mixedness model... 

All review sessions should be recorded using a personal computer (PC). Word processing software should be used for the report narrative write-up. A computer software spreadsheet, prepared for process safety reviews, should be used for all HAZOP and What-If reviews. It facilitates speed, ease of use and maintains exact consistency in format. 

Access to a compatible computer printer is needed to generate hard copies of the HAZOP or What-If software worksheets and word processor reports. 

A worksheet (data base spreadsheet) form is used to collect and collate the process hazard analysis review data. A computer software generated spreadsheet is typically used. For a complete description of commercially available HAZOP or What-If software, the user should refer to the manufacturer s HAZOP or What- If software User Instructions. Although pre-printed forms may be used, they are highly inefficient and should be maintained only as a backup in case of computer hardware or software failures. 

Copies of the HAZOP or What-If reports are to be prepared by the Team Leader and delivered to the project manager. The project manager is responsible to formally distribute copies of the reports. Information stored on computer software disks may be considered original copies. 

All costs are based on using a personal computer with standard HAZOP or What-If software support. Conducting a review without this similar support will lengthen its period. 

Standard spreadsheets and word processing software are typically available on business computers. Customized HAZOP and What-If spreadsheet software is available from several manufacturers and is either obtained by corporate overhead purchase or by specific location purchase. 

Chung, P. and Broomfield, E. (1995), Hazard and Operability (HAZOP) Studies Applied to Computer-Controlled Process Plants, in Computer Control and Human Error (Ed. T. Kletz), Institution of... 

Andow, P. (1991), Guidance on HAZOP Procedures for Computer Controlled Plants, Her Majesty s Stationery Office, London. 

Andow P. Guidance on HAZOP procesdures for computer-controlled plants. Contract research report No. 26/1991. Health and safety executive. KBC Process Technology Ltd. 1991. 

Type of process Generally, an initial screening is possible from the type of process involved. As stated earlier, FMEA is more suitable for computer systems and HAZOP is more suitable for process systems. Naturally based on the same PHA method, selection may be possible and needs to be judged with respect to other characteristics, for example, size and complexity. 

HAZOP is not suitable for electronic computer/mechanical production plants... 

The use of computers for HAZOP is quite common. In addition to automated HAZOP (discussed later), computerized recording is also available. The recording programs are basically special spreadsheets. This transition has resulted in thorough and quick recording of HAZOP studies. There are a number of features of use of computers for recording ... 

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