Computer HAZOP system

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. 

It is quite some time since various methods were developed for automating the HAZOP process. Some methods included computer-based systems. We shall now see how these systems have been developed. 

J.A. McDermid, M. Nicholson, D.J. Pumfrey, P. Fenelon, Experience with the Application of HAZOP to Computer-Based System, Internet document. 

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. ... 

However, a reasonable interpretation can be found only for part of the combinations the rest is meaningless and must be dropped. A short description of the HAZOP study can be found in [6] and [8] there are also specific standards available like [9] describing the procedure in detail. It has to be mentioned that HAZOP studies are today used for a wide variety of systems including electrical, electronic and computer controlled systems. 

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. 

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... 

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. 

V. Venkatasuhramanian, J. Zhao, S. Viswanathan, Intelligent systems for HAZOP analysis of complex process plants. Computers. Chemical Engineering (2000). Elsevier. 

See, e.g. P.Andow, Guidance on HAZOP procedures for computer-controlled plant, HSE Contract Research Report No 26/1991 andD.J.Bums R.M.Pitblado, A modified HAZOP methodology for safety-critical system assessment mDirections in safety-critical systems,... 

Kawamura, K. and Naka, Y. and Fuchino, A. and Aoyama, A. and Takagi, N., 2008. Hazop Support System And Its Use For Operation. Computer-Aided Chemical Engineering, 25, 1003-1008. 

Leone, H., 1996. A BCnowledge-Based system for HAZOP Studies. The knowledge Representation structure. European Symposium on Computer Aided Process Engineering—6. pp 363-374.1996. 

In the following sections, examples of the application of FMECA and HAZOP to two functional components will be described. The first component involves sample handling, the second the performance of the computer system file server. 

The conventional HAZOP documentation is supplemented to enable a review of computer control/PLC systems. The logic systems need to be as completely described as the PFD and P ED do for process systems and hardware. Several types of documentation are available ... 

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