Safe systems design

2 Contamination of metal hydrides - oxygen and water reactivity 

In this section, we will explore the safety properties of a specific set of complex hydrides, sodium alanates. These materials represent the most advanced solid-state hydrogen system developed to date and allow us to understand the safety properties associated with this class of materials. 

3 Sodium alanates prototypical complex metal hydrides 

This complex hydride absorbs and releases hydrogen in a two-step decomposition and recombination reaction shown in the following reaction  

The sodium alanates are high surface area materials that are pyrophoric and react readily with water. Intuitively, it would be expected that the system exothermically reacts to form NaOH and AI2O3 upon exposure to an oxidizing species. Despite the relatively benign oxidation products, some researchers have observed samples becoming friction sensitive after uncontrolled oxygen 

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Prescriptive design safety guidance provides a mechanism for implementing a safe system design at the beginning of a program before the entire set of necessary HAs and risk assessments can be completed. An effective SSP should be prescriptive (compliance) based and risk based however, risk based is the most important aspect because many hazards are unique to a particular system. 

Safety culture period Currently the importance of the culture of an enterprise in overarching Safe System design and operation is paramount. 

The absence of planning for transformational change is a widespread weakness in extant traffic safety strategies. Innovation is vital and can be best achieved through demonstration projects in the short term. Safe System design does not have to be prohibitive in cost. 

Stiller [29] focused his thesis on modeling-based design, operation and control of solid oxide fuel cell and gas turbine hybrid systems. He described the models used and examined three different hybrid cycles. The objectives for highly efficient and safe system design are formulated and its design parameters are associated. The analyzed system is a 220 kW unit with efficiency of 63%. Control strategy and partload performances are very similar to those which were described previously [27]. 

Concepts and Processes. Contemporary dosage forms are dmg dehvery systems, designed and manufactured to achieve safe and effective therapeutic responses each time the forms are used as part of an appropriate regimen. Thus, the intent of the prescriber is accompHshed when the product is used compliantly by the patient (12—14). Each dmg product involves several interrelated concepts that must be considered in its design and manufacture (15). Examples include the following ... 

The ultimate responsibility for safety rests with me operating company OSHA 1910.119 is clear on this. Each company is expected to develop (and enforce) its own practices in the design, installation, testing, and maintenance of safety systems. Fortunately, some companies make these documents public. Monsanto s Safety System Design Practices was published in its entirety in the proceedings of the International Symposium and Workshop on Safe Chemical Process Automation, Houston, Texas, September 27-29, 1994 (available from... 

Circuit capacitance and inductance, including the values of these parameters for interconnecting wiring, are integral parts of the overall analysis. It is not always possible to assure that the system will be maintained as designed with only approved intrinsically safe components and with circuits of the capacitance and inductance as originally installed. For this reason, intrinsically safe systems are used primarily at locations where there are sufficiently trained personnel to assure that the intrinsic safety of the system is always maintained. 

The filling method (See Figure 2) is essentially a fail-safe system in that controls are designed to prevent double-cycling. The filling valve and the reservoir valve are electrically interlocked so... 

An example for the design of fail-safe systems for the continuous sulfonation of an aromatic compound has been described [229]. This investigation was undertaken because a thermal explosion had occurred in a pump and circulation line. The total exothermic decomposition energy of the reaction mass is 500 kcal/kg, which is large. 

The scope of this book includes several aspects of safe process design and operation, such as the choice of reactor type, safe operating conditions, and the selection of protective systems, primarily related to chemical reactivity. However, even in a process plant where these aspects have been carefully considered and thoroughly applied, there are still numerous events that can occur and can lead to hazardous incidents. Examples of such events are ... 

Fail Safe - A system design or condition such that the failure of a component, subsystem or system or input to it, will automatically revert to a predetermined safe static condition or a state of least critical... 

The pneumatic test may be used in lieu of the hydrostatic test for hydrogen systems designed or supported so they cannot safely be filled with liquid, or if the vessel or system cannot be readily dried or is to be used in services in which traces of the testing liquid cannot be tolerated. The substitution requires that the parts of the system, when possible, are previously tested by hydrostatic pressure. The pneumatic test pressure should be 1.25 times the MAWP. 

Maturity of technology Although the principal technical elements for CCS are available, the entire system within a plant is not yet to be considered as mature. Stakeholders are concentrating on research and development of the components and of system design. In particular, safe and permanent C02 underground storage needs to be proven. 

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