Hazard severity definitions

Toxicology is the science of poisons but what is a poison The word poison conjures up many different ideas in people s minds and is often associated with the word chemical . Consulting various dictionaries, I found several definitions which were basically similar A substance that when introduced into or absorbed by Hving organisms causes death or injury—especially one that kills by rapid action even in small quantities . Another definition had an additional concept Any substance which taken into or formed in the body which destroys life or impairs health . Both definitions tell us that a poison is a substance that is hazardous to life, possibly lethaUy so. The first indicates that a poison is also likely to be potent and the second that it might be naturally produced. 

Each hazard class has associated placards and labels identifying the hazards of the class during transportation. Each hazard class and associated placard has a color, which indicates a particular hazard. Hazardous materials may have more than one hazard. It is important to note that the placard on a transport vehicle depicts only the most severe hazard of a material as determined by DOT hazard class definitions. When a material has more than one hazard, the DOT prioritizes the hazard that will be placarded. These hazards are listed by the DOT in 49 CFR 173.2a (see Figure 1.7) to determine which hazard will be assigned to a particular material when the material has multiple hazards. 

It must be understood that the charts on hazard severity and probabihty are to serve only as guides and that definitions of terms within them must be refined to suit the needs of a particular operation. 

The risk assessment code (RAC) matrix and the hazard severity and probability indices and definitions used in this study were taken from EMX-XXXX (the Facility System Safety Manual). 

Hazard severity, in Table 5.2, is a qualitative measure of the worst credible mishap resulting from the particular hazard cause. For more granularity, the hazard severity table can be quantified. For example, the safe distance or exclusion zone of an expanding toxic vapor cloud could be used to categorize hazard severity. You may also wish to expand the severity definitions and customize them to fit your particular operation. 

Risk management estabUshes the criteria that are necessary for the identification of hazards, assessing the risk inherent within those hazards and selecting the treatments or methods for the avoidance, control, transfer, or acceptance of risk. Before managing risk, several definitions are needed. 

Previous issues of MIL-STD-882 used the term hazard (defined as a condition that is a prerequisite to a mishap , and went on to define hazard severity and hazard probability levels (see Tables B.13 and B.14). This was definitively incorrect, as these categories described accidents (or mishaps) - not hazards. 

The correlation (or lack of correlation) of other physiochemical characteristics has not yet been established. For instance, are all surfactants irritants Can one classify severity by the size of the molecule Can octanol water partition coefficients predict irritation potential does a propensity to partition out of the ocular fluid mean that a compound presents more of an irritation hazard than one which is more water soluble Theoretically, these data should reflect the ability of a compound to penetrate the eye and cause an irreversible lesion. However, until definitive data are available, physical and chemical parameters will probably have limited utility in an overall assessment of irritation. 

Presented here is a glossary of terms related to the subject of this Concept Book. Several glossary entries are not used elsewhere in this publication. They have been included in case the user comes across an unfamiliar term in the course of managing chemical reactivity hazards. The Sources in the last column are all included in the reference list in the Reference section of this publication. Words in square brackets have been added to referenced definition. 

However, various countries use different definitions of chemical waste and there are often several inconsistencies in the definitions. Usually, the definiUon involves qualification of whether or not the material is hazardous. For example, in some counties, a hazardous waste is any material that is especially hazardous to human health, air, or water, or which is explosive, flammable, or may cause disease. Poisonous waste is material that is poisonous, noxious, or polluting and whose presence on the land is liable to give rise to an environmental hazard. But in more general terms (in any country), hazardous waste is waste material that is unsuitable for treatment or disposal in municipal treatment systems, incinerators, or landfills and which therefore requires special treatment. 

Fiber has been given a legal, if not operational definition, at least as it applies to asbestos. Unfortunately tlie definition bears little relationship to the present use of the term. It was essential to set standards to reduce occupational exposure but the detection, identification, and suppression of asbestos materials opened several areas of problems that remain unsolved. For example, six minerals are included in the definition of asbestos. Are they all equally hazardous If not, why not There are many other inorganic particles with diameters of less than 3 micrometers and a diameter-to-length ratio of 1 3. Should we be concerned that they too might be hazardous to our health ... 

These two definitions reflect two sides of the same situation. In this book, the term critical effect(s) will be used for the hazard/effect considered as being the essential one(s) for the purpose of the risk characterization, e.g., for the establishment of a health-based guidance value, permissible exposure level, or Reference Dose. It should be noted that the critical effect could be a local as well as a systemic effect. It should also be recognized that the critical effect for the establishment of a tolerable exposure level is not necessarily the most severe effect of the chemical substance. For example, although a substance may cause a serious effect such as liver necrosis, the critical effect for the establishment of, e.g., an occupational exposure limit could be a less serious effect such as respiratory tract irritation, because the irritation occurs at a lower exposure level. 

In the following, several terms used to describe interactions between chemicals are mentioned as well as basic concepts used in the hazard and risk assessment of chemical mixmres. The description of these basic concepts, first outlined by Bliss (1939) and Placket and Hewlett (1952), are based on the publications by Konemann and Pieters (1996), Cassee et al. (1998), and Groten et al. (2001). The definitions of additivity, synergism, antagonism, and potentiation are those of Klaassen (1995) and Seed et al. (1995). 

Included in Table 2 are several other definitions of toxicity ratings, drawn from different international legal or health authorities, e. g. the European Community, the German hazardous chemicals legislation and the US authorities. 

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