The purpose of this article is to discuss the way organizational factors are taken into account in the new breed of Probabilistic Risk Assessment methods. Methods, such as SHERPA (Embrey, 1986), IMAS (Embrey, 1992), WPAM (Davoudian, Wu, Apostolakis, 1994), SAM (Paté-Cornell, 1993; Paté-Cornell, Fischbeck, 1993; Paté-Cornell, Murphy, 1996), have attracted increased attention from various industrial communities. After a first generation of methods pertaining to evaluate "human error", a couple of serious systemic accidents (Shrivastava, 1987, Vaughan, 1996, Reason, 1987, Paté-Cornell, 1993) urged experts to look at the organization, long considered as a black box. This movement was a much needed response to the discovery of the importance of organization in the good functioning of complex systems (Perrow, 1984, Turner, 1979).

We evaluate these methods, from two vantage points related to our respective research background on complex organizations (Abramovici, 1997, 1998a, 1998b; Bourrier, 1996a, 1996b, 1998a, 1998b) : a) The sociologist view, which focuses on actors in order to evaluate the social construction and the dynamics of organizational reliability, b) the risk management view which looks at the tools that managers use in order to ensure the performance of the systems. More specifically, we question these methods' declared objectives, the nature of the organizational data used and the way these ones are related to the functioning of the system.

The paper is organized as follow : 1° After having briefly recalled the evolutions of PRAs over the last 30 years, we will describe the engineering, (the "works") of the methods, then 2° secondly, based on this intimate knowledge we will underline the limits of those methods. Indeed it is our analysis that these methods fall short of offering sound and robust knowledge of organizational mechanisms influencing safety. The elements they are using to quantify the influence of organizational factors on safety rely upon a mechanistic and normative view of organizational mechanisms, which cannot account for the diversity and complexity that we observed. 3° Finally, we will show some directions of research that we believe are useful if one wants to seriously progress into the understanding of these complex systems.

Abramovici, M., La prise en compte des facteurs organisationnels dans les méthodes d'analyse des risques. Note de recherche N° 96-07, Groupe de recherche sur le Risque, l'Information et la Décision, 1996.

Abramovici, M., "Accidents industriels : la mise en cause impossible de l'organisation", Préventique-Sécurité, N°39, pp. 64-73, 1998.

Abramovici, M. & M. Poumadère, "La culture organisationnelle : un enjeu pour la fiabilité des systèmes", papier présenté au colloque "maintenabilité et fiabilité, Arcachon, 29 Septembre- 1 Octobre 1998.

Bourrier, M., "Organizing Maintenance Work at Two American Power Plants", Journal of Contingencies and Crisis Management, Vol. 4, N°2, june, p. 104-112, 1996.

Bourrier, M., Une analyse de la fiabilité organisationnelle, organisation des activités de maintenance dans quatre centrales nucléaires en France et aux Etats-Unis, PhD in Sociology, 2 volumes, 480 p., Institut d'Etudes Politiques de Paris, December 1996.

Bourrier, M., "Elements for Designing a Self-Correcting Organization : Examples from Nuclear Power Plants". Chap. 8 in Safety Management and the Challenge of Organizational Change, M. Barram and A. Hale (eds), forthcoming

Bourrier, M., "Constructing Organizational Reliability : the Problem of Embeddedness and Duality", in Nuclear Power Plant Safety in Human Factors Perspective, Wilpert, B. (ed), London: Taylor and Francis, forthcoming.

Davoudian, K.; Wu, J.; Apostolakis, G., "Incorporating organizational factors into risk assessment through the analysis of work processes", Reliability Engineering and System Safety, Vol. 45, pp. 85-105, 1994.

Davoudian, K.; Wu, J.; Apostolakis, G., "The Work Process Analysis Model (WPAM)", Reliability Engineering and System Safety, Vol. 45, pp. 107-125, 1994.

Embrey, D.E., "SHERPA : A Systematic Human Error Reduction and Prediction Approach", Proceedings of Advances in Human Factors in Nuclear Power Systems Meeting, Knoxville, pp 184-193 1986

Embrey, D.E., "Incorporating Management and Organisational Factors into probabilistic safety assessment", Reliability Engineering and System Safety, Vol. 38, pp. 199-208, 1992.

Paté-Cornell, E.; Fischbeck, P., "P.R.A. as a management tool : organizational factors and risk-based priorities for the maintenance of the tiles of the space shuttle orbiter", Reliability Engineering and System Safety, Vol. 40, pp. 239-257, 1993.

Paté-Cornell, E.; Murphy, D., "Human and management factors in probabilistic risk analysis: the SAM approach and observations from recent applications", Reliability Engineering and System Safety, Vol 53, pp. 115-126, 1996.

Perrow, C., Normal Accidents, living with High Risk Technologies, New York, Basic Books, 1984.

Reason, J., "The age of organizational accident", Nuclear Engineering International, p.18-19, 1987.

Shrivastava, P., Bhopal: Anatomy of a Crisis, Cambridge, MA, Ballinger, 1987.

Turner, Barry, "The organizational and Interorganizational Development of Disasters", Administrative Science Quarterly, Vol. 21, pp. 378-397, 1976.

Vaughan, D., The Challenger Launch Decision, Chicago, the University of Chicago Press, 1996.

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