Karel Soudan

Consequences of deltoid muscle elongation on deltoid muscle performance: a computerised study

BACKGROUND The deltoid muscle plays an important role in normal shoulder function. Knowledge of the position of the glenohumeral rotational centre and of the deltoid muscle length is essential to understand optimal placement of a total shoulder prosthesis. OBJECTIVE This study is designed to analyse the effect of deltoid muscle elongation on shoulder joint function. DESIGN A three-dimensional model of the glenohumeral joint with deltoid muscle analysis in the scapular plane. METHODS A geometrical three-dimensional ball-and-socket model of the shoulder joint was developed. From dry bones, the position of the origins and insertions of the three parts of the deltoid muscle relative to the calculated centre of rotation of the humeral head was defined. The position and the direction of the muscle force working lines relative to this humeral centre were calculated using former measurements and CT-data of the deltoid. Muscle length-tension data were applied to obtain angle-force relationships. The model was used to calculate the angle-force relationships, the moment arm and the moment of the deltoid muscle components for successive arm elevation angles in the scapular plane. These data were compared to those of a theoretical situation assuming a 10% elongation of the muscle. RESULTS Muscle angle-force curves show a more favourable slope after moderate (10%) deltoid muscle elongation. Elongating the muscle by changing the distance between the humeral rotation point and the deltoid insertion along the humeral axis does not affect moment arms. The moments of the deltoid muscle forces themselves, however, seem more adapted to elevation in the scapular plane. The deltoid maximal moment exceeds the arm-weight moment by about 40% instead of being approximately equal, and that the maximum is situated around 100 degrees of elevation. CONCLUSIONS From a biomechanical point of view, stretching the deltoid muscle by 10% seems to result in a significantly more favourable position in case of shoulder elevation at 90 degrees of abduction in the scapular plane in a centred glenohumeral joint. RELEVANCE This model suggests that a 10% elongation of the deltoid muscle, the most important shoulder abductor, improves its ability to elevate the arm. If properly implemented, this observation can be very important in the treatment and early rehabilitation of rotator-cuff-insufficient shoulders treated by a specific total shoulder replacement design.

A game-theoretical approach for reciprocal security-related prevention investment decisions

Every company situated within a chemical cluster faces important security risks from neighbouring companies. Investing in reciprocal security preventive measures is therefore necessary to avoid major accidents. These investments do not, however, provide a direct return on investment for the investor-company and thus plants are hesitative to invest. Moreover, there is likelihood that even if a company has fully invested in reciprocal security prevention, its neighbour has not, and as a result the company can experience a major accident caused by an initial (minor or major) accident that occurred in an adjacent chemical enterprise. In this article we employ a game-theoretic approach to interpret and model behaviour of two neighbouring chemical plants while negotiating and deciding on reciprocal security prevention investments.

Developing an external domino accident prevention framework

Empirical research on major accident safety in the second largest chemical cluster worldwide, the Antwerp port area, supports the design of a meta-technical framework for optimizing external domino prevention. First, the majority of Seveso top tier companies have expressed a willingness to cooperate more intensively to protect themselves against potential off-site major accidents. Second, Hazop, What-If analysis and the Risk Matrix, interesting building blocks for such a framework, are frequently used risk analysis techniques at Seveso lower tier and Seveso top tier companies. The developed framework, called Hazwim, integrates these three complementary techniques into an effective standardized risk analysis framework for the prevention of external xdomino accidents in an industrial area. The main strengths of Hazwim are its completeness and its cost-effectiveness. The combination of techniques on the one hand and qualitative and quantitative data on the other, offers a comprehensive up-to-date list of cross-company domino hazards and recommended actions in the area under consideration. The Hazwim framework offers support to prevention managers and safety policy makers concerning external domino prevention.

Making evacuation decisions by using a discrete-time approximation methodology.

This article further elaborates the findings by Reniers et al. in 2007 and 2008. A discrete-time approximation is presented to determine the severity of a major accident threat triggering immediate evacuation and its expected resulting costs. By implementing the proposed mathematical model, precautionary evacuation decision problems can be tackled in a realistic way, i.e., allowing for major accident threats with limited duration. Furthermore, the model is moulded into a working procedure which was used to develop software to solve the suggested algorithms. A case-study is provided and the results obtained by application of the methodology are discussed. Using a (realistic) discrete-time approximation computer simulation, we found that ignoring option characteristics may produce suboptimal intervention decisions in shutdown settings.

The use of current risk analysis tools for preventing external domino accidents

Risk analysis is an essential tool for company safety policy. Risk analysis consists of identifying and evaluating all possible risks. The efficiency of risk analysis tools depends on the rigueur of identifying and evaluating all possible risks. The diversity in risk analysis procedures is such that there are many appropriate techniques for any circumstance and the choice has become more a matter of taste. In this paper, we examine the risk analysis tools used by 24 chemical plants in Belgium, mainly located in the port of Antwerp, the second largest chemical cluster in the world after Houston, TX, USA. The aim of this paper is to identify the current practice in the chemical industry subject to European Seveso legislation and to examine how the present methods can be integrated to improve safety policy, especially towards preventing major accidents. Moreover, conclusions on the prevention of catastrophic external domino accidents involving several companies are formulated. This paper also gives impulse to investigating cross-company management implementations concerning external domino accident prevention.

Empirical validation of a real options theory based method for optimizing evacuation decisions within chemical plants

This article empirically assesses and validates a methodology to make evacuation decisions in case of major fire accidents in chemical clusters. In this paper, a number of empirical results are presented, processed and discussed with respect to the implications and management of evacuation decisions in chemical companies. It has been shown in this article that in realistic industrial settings, suboptimal interventions may result in case the prospect to obtain additional information at later stages of the decision process is ignored. Empirical results also show that implications of interventions, as well as the required time and workforce to complete particular shutdown activities, may be very different from one company to another. Therefore, to be optimal from an economic viewpoint, it is essential that precautionary evacuation decisions are tailor-made per company.

Chemical Industrial Areas and their Dynamic Danger Behaviour

Chemical industrial areas or so-called chemical clusters consist of various companies situated next to each other. Such areas are composed of hundreds of chemical installations exhibiting danger to a certain degree for initiating or continuing knock-on effects. In this paper, a methodology to model such clusters as networks and to investigate their dynamic danger behaviour is proposed. This original approach leads to a tentative strategy to optimally protect chemical industrial areas against security risks.