The VIRTHUALIS project aims to develop a number of virtual reality applications for improving safety in the process industries. The applications allow human factors experts to study how operators interact with plant, and provide a safe environment in which new safety actions can be tried and tested. Safety applications are built on the SafeVR technology platform, a distributed client-server virtual reality system. This paper describes how two external modules -a process simulator and a rule-based system -are interfaced to the platform and the benefits they provide both separately and together. The two modules communicate with the platform's server by exchanging messages, conforming to a simple syntax. pSimProxy provides a generic interface to an external process simulator, which in turn delivers the realistic plant behaviour. It handles bidirectional data exchange with and control of the external simulator. It can be configured at run time to use whichever available mechanisms are supported by the actual process simulator that models the plant being simulated. ClipsClient is an expert or rule-based system, based on NASA's CLIPS expert system software that can make inferences about the information contained in the messages. It consists of a set of facts, a number of rules and an inference engine. It can be provided with a number of rules that monitor how operators are running the plant, and react in useful ways to these events. The simulator notifies the server of changes in process parameters through a message. The values may be displayed, for example as gauge readings, in the virtual environment. As operators control the plant, their actions, say opening a valve, are also reported by messages via the server to the process simulation. Messages can also be read by the rule-based system, allowing it to maintain its own representation of the plant. This in turn permits automated expert reasoning on the state of the plant and the actions of its operators which can cause further message to be sent to the server. The rule-based system is therefore, a powerful mechanism for rapidly reconfiguring the application and general rules can be written that only require new facts at run-time to change the behaviour of the entire virtual environment. The message syntaxes, the system architecture and the interfacing of the external modules are described along with examples showing their individual and joint benefits.

A study has been made of the relation between breaking time and breaking load for six different fabrics, using 1-in. ravelled strips with 3-in. initial clamp separation, tested on a constant-rate-of-specimen-extension (CRE) machine operated at a number of rates of extension, i.e., cross-head speed. The fabrics used were cotton nainsook, heavy cotton duck, acetate/viscose gabardine, viscose crepe, and nylon taffeta, so as to cover a range of extensibilities and breaking loads. In general these fabrics showed a decrease in breaking load with increase in breaking time, as has also been reported in the literature for studies on fibers and yarns. Tests were also carried out on constant-rate-of-traverse (CRT) pendulum machines at two or three different speeds for each fabric. Good agreement was obtained between the breaking loads measured on the CRE and CRT machines when compared at equal breaking times. To put the measurement of breaking load of fabrics on a constant-breaking-time basis appears to offer the best means of obtaining comparable results with different types and capacities of testing machines. A breaking time of 20 ± 3 sec. has recently been proposed by ISO/TC 38 for single-strand testing of yarns on CRE, CRT, and CRL (constant-rate-of-loading) machines. The data obtained in this study on fabrics suggest that a breaking time of 20 ± 3 sec. will also be suitable for the measurement of the break ing load of fabrics on different types and capacities of machines. No evidence was ob tained in favor of a longer breaking time such as the 60 ± 10 sec. commonly used with CRL machines abroad.