Potential hazards, identifications

Presently, quantitative health hazard and exposure data are not available for most nanomaterials. Therefore, health risk evaluation for the workplace currently relies to a great degree on professional judgments for hazard identification, potential exposures and the application of appropriate safety measures. 

Fire and Explosion Index (Ffrom fires and explosions. frequency The rate at which observed or predicted events occur. HAZOP HAZOP stands for hazard and operabihty studies. This is a set of formal hazard identification and ehmination procedures designed to identify hazards to people, process plants, and the environment. See subsequent sections for a more complete description. 

The hazard identification step of the QRA typically requires the greatest involvement of plant personnel. For an existing process, only plant personnel know the status of process equipment and the current operating and maintenance practices. Excluding those personnel from the hazard identification step increases the chance of overlooking important potential hazards. For accurate results, the QRA team must have access to this information. 

The cost of performing the hazard identification step depends on the size of the problem and the specific techniques used. Techniques such as brainstorming, what-if analyses, or checklists tend to be less expensive than other more structured methods. Hazard and operability (HAZOP) analyses and failure modes and effects analyses (FMEAs) involve many people and tend to be more expensive. But, you can have greater confidence in the exhaustiveness of HAZOP and FMEA techniques—their rigorous approach helps ensure completeness. However, no technique can guarantee that all hazards or potential accidents have been identified. Figure 8 is an example of the hazards identified in a HAZOP study. Hazard identification can require from 10% to 25% of the total effort in a QRA study. 

The hazard identification step is perhaps the most important, because any hazard not identified will not be considered in the decision process. For example, the impact of chlorofluorocarbons on atmospheric ozone was unknown for much of the period of their use, and this potential hazard was not considered until recent years. 

Hazard identification, step one, means identification of new chemicals or other factors that may cause harmful health effects. Previously, novel hazards were usually observed in case studies or after accidents or other excessive exposures, usually in occupational environments. Today, thorough toxicity studies are required on all pesticides, food additives, and drugs. New chemicals also have to be studied for their potential toxic effects. Thus, earlier hazards were in most cases identified after they had caused harmful effects in humans. Today, most chemical products have been evaluated for their toxicity with experimental animals. Therefore, hazard identification has become a preventive procedure based on safety studies conducted before a chemical compound or product reaches the market, and before individuals are exposed to it. ... 

Management must modify the culture and develop human factors awareness in the hazard identification teams so that they will be capable of identifying the potential for human error. A good practice is to involve operators in the hazard identification team. 

Most human or environmental healtli hazards can be evaluated by dissecting tlie analysis into four parts liazard identification, dose-response assessment or hazard assessment, exposure assessment, and risk characterization. For some perceived healtli liazards, tlie risk assessment might stop with tlie first step, liazard identification, if no adverse effect is identified or if an agency elects to take regulatory action witliout furtlier analysis. Regarding liazard identification, a hazard is defined as a toxic agent or a set of conditions that luis the potential to cause adverse effects to hmnan health or tlie environment. Healtli hazard identification involves an evaluation of various forms of information in order to identify the different liaz.ards. Dose-response or toxicity assessment is required in an overall assessment responses/cffects can vary widely since all chemicals and contaminants vary in their capacity to cause adverse effects. This step frequently requires that assumptions be made to relate... 

Generally, the main pathways of exposure considered in tliis step are atmospheric surface and groundwater transport, ingestion of toxic materials that luu c passed tlu-ough the aquatic and tcncstrial food chain, and dermal absorption. Once an exposure assessment determines the quantity of a chemical with which human populations nniy come in contact, the information can be combined with toxicity data (from the hazard identification process) to estimate potential health risks." The primary purpose of an exposure assessment is to... 

There arc oilier methods of hazard identification. A "wliat-if analysis presents certain questions about a particular hazard and then tries to find llie possible consequences of that hazard. The human-error analysis identifies potential human errors that will lead to an accident. They can be used in conjunction with llic two previously described methods.. ... 

Hazard identification provides information on situations or chemicals tliat can potentially liann tlie environment, life, or property. Tlie processes described are process checklist, event tree, hazard and operability study. 

As indicaled above, the PHA may ser c as a precursor lo further hazard analyses. It is included in lliis chapter because it can pro ide a cost effective, early-on plant method for hazard identification. As its title indicates, the PHA is really intended for use only in the preliminary phase of plant development for cases where past e.spcriencc provides little or no insight into any potential safety problems, e g., a new plant with a new process. 

Adapted from H. Karranian, J.K. Rao and F.V. Hour, Application of Hazard Evaluation Teclmiqucs to tlic Design of Potential Hazardous Identification in Chcniical Processes, NlOSH, Cincinnati, Olrio, 1992. 

At present the approach to assessing the potential risks of exposure to a chemical in the diet involves the application of a standardised risk assessment approach consisting of three main elements - hazard identification and characterisation and exposure assessment. 

During the identification step, the potential hazards and methods of contact are identified and recorded. As illustrated in Table 3-5, the potential hazards are numerous, especially because the listed hazards can also act in combination. This fist of potential hazards together with the required data for hazard identification (see Table 3-6) is commonly used during the identification step of industrial hygiene projects. 

Hazard identification can be performed independent of risk assessment. However, the best result is obtained if they are done together. One outcome is that hazards of low probability and minimal consequences are identified and addressed with the result that the process is gold-plated. This means that potentially unnecessary and expensive safety equipment and procedures are implemented. For instance, flying aircraft and tornadoes are hazards to a chemical plant. What are the chances of their occurrence, and what should be done about them For most facilities the probability of these hazards is small No steps are required for prevention. Likewise, hazards with reasonable probability but minimal consequences are sometimes also neglected. 

Various hazard identification criteria can be defined if sufficient knowledge of the process and of the equipment is available such that a mathematical model of the overall process can be constructed. The model can then be used to detect a hazardous situation, such as a runaway, developing at an early stage. This technique has potentially the highest predictive power, but does require an extensive knowledge of the chemical process and of the equipment characteristics. However, fully sufficient models are rarely available and their development is time consuming. 

PHA focuses on the hazardous materials and major plant elements in the process plant to provide a cost-effective hazard identification [2, 3]. It is intended for use in the early design stage and it can be very useful in site selection. It also provides early guidance to plant designers in considerations for reducing or eliminating potential hazards. 

Hazard identification is akin to the qualitative prediction of impacts in EIA and is largely accomplished when the EIA is performed independently of, or prior to, an ERA. The potentially significant risks are often identified because of experience elsewhere with similar materials, processes, ecosystems, and conditions. This step is immediately useful to management and helps to sharpen the question posed in the... 

Hazard and Operability Analysis (Hazop) (Kletz, 1992) is one of the most used safety analysis methods in the process industry. It is one of the simplest approaches to hazard identification. Hazop involves a vessel to vessel and a pipe to pipe review of a plant. For each vessel and pipe the possible disturbances and their potential consequences are identified. Hazop is based on guide words such as no, more, less, reverse, other than, which should be asked for every pipe and vessel (Table 1). The intention of the quide words is to stimulate the imagination, and the method relies very much on the expertise of the persons performing the analysis. The idea behind the questions is that any disturbance in a chemical plant can be described in terms of physical state variables. Hazop can be used in different stages of process design but in restricted mode. A complete Hazop study requires final process plannings with flow sheets and PID s. 

Also indices such as the Dow Fire and Explosion Hazard Index and the Mond Index have been suggested to measure the degree of inherent SHE of a process. Rushton et al. (1994) pointed out that these indices can be used for the assessment of existing plants or at the detailed design stages. They require detailed plant specifications such as the plot plan, equipment sizes, material inventories and flows. Checklists, interaction matrices, Hazop and other hazard identification tools are also usable for the evaluation, because all hazards must be identified and their potential consequences must be understood. E.g. Hazop can be used in different stages of process design but in restricted mode. A complete Hazop-study requires final process plans with flow sheets and PIDs. 

Figure 23-1 shows the hazards identification and risk assessment procedure. The procedure begins with a complete description of the process. This includes detailed PFD and P I diagrams, complete specifications on all equipment, maintenance records, operating procedures, and so forth. A hazard identification procedure is then selected (see Haz-ard Analysis subsection) to identify the hazards and their nature. This is followed by identification of all potential event sequences and potential incidents (scenarios) that can result in loss of control of energy or material. Next is an evaluation of both the consequences and the probability. The consequences are estimated by using source models (to describe the... 

Logic Model Methods The following tools are most commonly used in quantitative risk analysis, but can also be useful qualitatively to understand the combinations of events which can cause an accident. The logic models can also be useful in understanding how protective systems impact various potential accident scenarios. These methods will be thoroughly discussed in the Risk Analysis subsection. Also, hazard identification and evaluation tools discussed in this section are valuable precursors to a quantitative risk analysis (QRA). Generally a QRA quantifies the risk of hazard scenarios which have been identified by using tools such as those discussed above. 

---