Safety general measures

Chapter 1 provided a general research area, where the problem of measuring safety pro-actively was identified in literature and in practice. This was done by sketching a recent accident and discussing how safety was measured in the past and currently. Moreover, it highlighted that the pro-active measurement of safety is still a problem in the chemical process industry. The development of substantially more understanding of how to pro-actively indicate accidents in the chemical process industry, was finally derived as the scope of this study and will be discussed in the remaining Chapters of this thesis. 

Zwart, D., Langelaan, M., van de Vooren, R.C., Kuyvenhoven, M.M., Kalkman, C.J., Verheij, T.J.M. and Wagner, C. 2011. Patient safety culture measurement in general practice Clinimetric properties of SCOPE. BMC Family Practice, 12(1), 117. 

The research into safety culture has led to the use of safety climate measurement tools as a Safety Performance Indicator (Guldenmund, 2000) but the results are largely intangible and may not help organizations identify where they need to focus attention in order to improve safety (Sorenson, 2002). The lack of a generally accepted definition for safety culture or safety chmate also limits their usefulness as concepts since they do not support a systemic methodology for their measurement (Zhang et al., 2002). 

Overall, the sizing method according to EN-ISO 4126-7 is based on very simple equations mainly for ideal gases. In the literature, the validity of this sizing method was shown by numerical calculations up to pressures of about 10 MPa (100 bar) [3,4]. No limits of application are formulated in the standards for high-pressure valves. In addition, the discharge coefficients for safety valves are generally measured at pressures between 0.1 and 5 MPa - the application limit of current test facilities amounts to about 25 MPa (250 bar). The question arises whether the application of the current standard beyond a pressure of more than 10 MPa is allowed. 

Risk is a combination of the probability and the degree of the possible injury or damage to health in a hazardous situation (British Standard (1991)). Safety is the ability of an entity not to cause, under given conditions, critical or catastrophic consequences. It is generally measured by the probability that an entity, under given conditions, will not cause critical or catastrophic consequences (Villemuer (1992)). 

Finally, under the heading Specific pressure equipment requirements specific requirements are set out for equipment with a risk of overheating, for piping and, last but not least, specific quantitative requirements which set out a series of safety factors for certain pressure equipment. These latter provisions apply as a general rule which means that a manufacturer or a harmonised standard may deviate from these factors if it can be demonstrated that appropriate measures have been taken to achieve an equivalent level of safety. 

Figure 16.6 shows the general yield and fast fracture loci for a pressure-vessel steel and an aluminium alloy. The critical flaw size in the steel is =9 mm that in the aluminium alloy is =1 mm. It is easy to detect flaws of size 9 mm by ultrasonic testing, and pressure-vessel steels can thus be accurately tested non-destructively for safety -vessels with cracks larger than 9 mm would not be passed for service. Raws of 1 mm size cannot be measured so easily or accurately, and thus aluminium is less safe to use. 

The best anti-surge control is the simplest and most basic that will do the job. The most obvious parameter is minimum-flow measurement, or if there is a relatively steep pressure-flow characteristic, the differentia pressure may be used. The latter parameter allows for a much faster response system, as flow measurement response is generally slow however, the speed of response need only be fast enough to accept expected transients. One major problem with the conventional methods of measurement and control is the need to move the set point for initiation of the control signal away from the exact surge point to allow some safety factor for control response time and other parameters not directly included... 

The following safety measures supplement the general preeautions listed in Table 9.3 ... 

Aim to protect the health and safety of everyone m the workplace and ensure that adequate welfare facilities are provided. Covers e.g. general ventilation, temperature m indoor workplaces, lighting, cleanliness, space requirements, condition of floors and traffic routes, measures against falls/fallmg objects, washing facilities. 

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