Types of Hazards and Hazardous Events

Undesired reactions catalyzed by materials of construction or by ancillary materials such as pipe dope and lubricants Boiling liquid, expanding vapor explosions (BLEVEs) 

Toxic to individual species or broadly hazardous Pesticides, fungicides, herbicides, insecticides, fumigants Toxic to humans Chronic or acute 

Reversible injury or irreversible injury or death Carcinogens 

A flammable vapor explosion in a vessel initially at atmospheric pressure can create a pressure of 10 atmospheres (NFPA 69, 1992, Section 5-3.3.1). A weak process vessel requires substantial vent area for vapor-air explosion relief. 

A flame in a pipeline containing a flammable mixture can transition to a detonation. This flame-to-detonation transition is discussed in Lewis and von Elbe (1987, Section 8.5). 

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Table 4.1 is a representative list of the types of hazards and hazardous events that research chemists are attempting to address in searching for the best chemistry. Some key factors to consider relative to process hazards include ... 

The accuracy of absolute risk results depends on (1) whether all the significant contributors to risk have been analyzed, (2) the realism of the mathematical models used to predict failure characteristics and accident phenomena, and (3) the statistical uncertainty associated with the various input data. The achievable accuracy of absolute risk results is very dependent on the type of hazard being analyzed. In studies where the dominant risk contributors can be calibrated with ample historical data (e.g., the risk of an engine failure causing an airplane crash), the uncertainty can be reduced to a few percent. However, many authors of published studies and other expert practitioners have recognized that uncertainties can be greater than 1 to 2 orders of magnitude in studies whose major contributors are rare, catastrophic events. 

Thermo-diffusion calculations analyze the migration of hazardous material from compartment to compartment to release in containment. These calculations use physico-chemical parameters to predict the retention of hazardous materials by filtration, deposition on cold surfaces and other retention processes in the operation. Containment event trees aid in determining the amount, duration and types of hazardous material that leaves the containment. 

A note on safety Some of the activities call for chemicals or reagents that are toxic in some way and/or produce toxic vapors under some conditions. Individuals working with these materials need to understand the types of hazards involved, how to protect themselves and those around them from these hazards, and how to proceed in the event of a spill or accident. Read the entire activity before proceeding Note the safety precautions and follow them. Chemi-... 

Perform an in-depth investigation of any operational anomalies, including hazardous conditions (such as water in a tank that will contain chemicals that react to water) or events. Determine why they occurred before any potentially dangerous operations are started or restarted. Provide the training necessary to do this type of investigation and proper feedback channels to management. 

OSHA stresses the importance of a team-based approach to all types of hazards analysis, but such an approach is fundamental for those techniques that fall into the first category, i.e., those that are primarily creative or imaginative. (Other techniques such as fault tree analysis are less suitable for team participation. However, even in such cases, a team is needed to identify the base events, and to discuss the cause and effect relationships that exist within the system being analyzed.)... 

For example, the FTA approach is logical and rational. The persons building the tree assume that the base events, and the manner in which they interact with one another, have been defined before the analysis starts. However, fault tree analysts will often identify new incident scenarios and find new types of hazard. In other words, this logical/rational approach to hazards analysis can also be creative and imaginative. ... 

This type of hazards analysis can be either deductive or inductive. A deductive (top-down) analysis is one that first defines an undesirable event, and then considers what events and chains of circumstances are needed to occur before the overall undesirable event occurs. A deductive approach is used by detectives to solve crimes. A widely used type of deductive analysis in process risk analysis is the fault tree method, described in the next chapter. 

Note These criteria are based on failure probability (not accident probability). The accident/risk-based criteria (e.g. from Def Stan 00-56 or MIL-STD-882) consider die probability of the consequence (i.e. the accident) of various types of hazards. It is in this aspect that the accident/risk-based approach is difficult to apply, because a system target can only be set after an accident risk is defined and the accident sequence is fully populated with the probability of each contributing cause/event. For more information, see Kritzinger (2005), Chapters 4 and 5. When considering the use of risk (i.e. die product of accident probability and accident severity), please do ke in mind ... 

Performing a hazard and risk analysis is one of the first steps that must be done when designing hoist and haul systems. The hazard and risk analysis will include all possible hazardous events that can occur. Annex B in [ISO 12100] gives support during the hazard and risk analysis by listing different types of hazards ... 

For each of these types of hazards different kinds of hazardous events can occur. For each identified hazardous event it is necessary to determine its severity and probabihty to be able to identify whether any risk reduction measures are necessary or not. Chapter 6.5 in [ISO/TR 14121-2] describes a hybrid tool to determine whether risk reduction is necessary or not for the identified hazardous events. 

Risk assessment involves a combination of various risks based on different types of consequences. Information on the historic record of hazard events, frequency-magnitude and triggering mechanisms provides additional insight for the recognition of risk sites and risk level. Further parameter calibration and expert judgment are required for practical risk management. 

This section describes the important underlying physical mechanisms for some of the more common types of hazardous material releases and gives guidance on the type of models that should be used to provide an acceptable level of accuracy in estimates of event consequences (and hence individual risk, which is the desired end point for comparison against the MIACC risk acceptability guidelines). 

Here, the integration essentially represents the total amount of contaminant or thermal energy received by the receptor (weighted by the power n), and n is an empirical PROBIT parameter appropriate for the chemical and type of hazard. The integration is performed over the time of exposure during the hazardous event. (Effect of evacuation or sheltering in a building can thus be incorporated into the results if desired.)... 

Because the above scheme does not define the relationship between hazardous events and states, we prefixed each risk score with the letter E or S to indicate which type of hazard it was. Thus a risk score might be quoted as EOS or S07 and references to the E09 hazards soon became part of the project vocabulary. It was also widely appreciated that an EOS hazard represented a 10-fold increase in risk over an E07 hazard and that ten E07 hazards were equivalent to one EOS hazard. 

CCFs create the subtlest type of hazards because they are not always obvious, and they can be difficult to identify. The potential for this type of event exists in any system design that relies on redundancy or uses identical components or software in multiple subsystems. CCF vulnerability results from system failure dependencies inadvertently designed into the system. Another example of a CCF would be the forced failure of two independent, and redundant, hydraulic flight control systems due to a failure event that cuts both hydraulic... 

Reducing, as far as reasonably achievable, the core damage frequency, taking into account aU types of hazards and failures and combinations of events, and the releases of radioactive material from all sources, providing due consideration to siting and design to reduce the impact of aU external hazards and malevolent acts. 

A consequence-based approach that takes into consideration the impact of explosions, fires, and toxic releases based on maximum credible events for each budding and type of hazard considered. 

Identification of hazards and listing of initial events such as gas leakage. This work is based on generic information about the type of concept, and operational experience plays a minor role. 

An accident stands for just one of several possible outcomes of man-machine interactions in hazardous situations. The kinds of near misses or conflict patterns where actual injuries are avoided are far more common. Incidents and conflicts can be used to gain sufficient and reliable information on the underlying accident conditions due to their increased likelihood as compared to the rare events of accidents themselves. The critical incident technique calls for the description of near misses in recently experienced work situations (Flanagan 1954). The traffic conflicts technique is an observation tool and samples different types of near accidents to identify unsafe technical conditions of the traffic location observed, types of unsafe behavior of drivers, cyclists and pedestrians, as well as types of hazardous traffic regulations (Zimolong 1982, Erke Gstalter 1985). 

Consequence Phase 3 Develop Detailed Quantitative Estimate of the impacts of the Accident Scenarios. Sometimes an accident scenario is not understood enough to make risk-based decisions without having a more quantitative estimation of the effects. Quantitative consequence analysis will vary according to the hazards of interest (e.g., toxic, flammable, or reactive materials), specific accident scenarios (e.g., releases, runaway reactions, fires, or explosions), and consequence type of interest (e.g., onsite impacts, offsite impacts, environmental releases). The general technique is to model release rates/quantities, dispersion of released materials, fires, and explosions, and then estimate the effects of these events on employees, the public, the facility, neighboring facilities, and the environment. 

Since dependency analysis is not needed, we can go on to the BUILD program. Go to FTAPSUIT and select 5 "Run Build." It asks you for the input file name including extender. Type "pv.pch," It asks you for name and extender of the input file for IMPORTANCE. Type, for examle, "pv.ii . It next asks for the input option. Type "5" for ba.sic event failure probabilities. This means that any failure rates must be multiplied by their mission times as shown in Table 7.4-1. (FTAPlus was written only for option 5 which uses probabilities and error factors. Other options will require hand editing of the pvn.ii file. The switch 1 is for failure rate and repair time, switch 2 is failure rate, 0 repair time, switch 3 is proportional hazard rate and 0 repair time, and switch 4 is mean time to failure and repair time.)... 

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