What Is Hazardous?

A material of relatively low hazard can present substantial risk, while a material with a high hazard might present no measurable risk in certain circumstances.

There are thousands, if not millions, of chemical substances in the world’s marketplace, and in our homes, schools, churches, workplaces, public facilities and in the ambient environment. Chemicals are found everywhere. They purify drinking water, increase crop production, simplify household chores, and are used to manufacture our products. But chemicals can also be hazardous to humans or to the environment when used or released improperly. Hazards can occur during production, storage, transportation, handling, use, or disposal. You, your workplace, and your community are at risk if a chemical substance is used unsafely or released in harmful amounts into the environment where you live, work, or play.

We talk about it all the time, but just what is hazardous?

Hazardous Material vs. Hazardous Waste
A hazardous waste is any discarded material containing substances known to be toxic, mutagenic, carcinogenic, or teratogenic to humans or other life forms; it may be ignitable, corrosive, explosive, or highly reactive alone or with other materials. A hazardous waste is always a hazardous material, although a hazardous material is not always a hazardous waste.

A hazard is a situation that poses a level of potential threat or risk, to life, health, property, or environment. Most hazards are dormant or potential, with only a theoretical risk of harm; however, once a hazard becomes "active," it can create an emergency situation. More directly, a hazard is a source of potential harm or negative outcome from past, current, or future exposures.

The term hazardous refers to a condition, circumstance, or combination of factors that create a substantial risk or danger of causing injury to persons or damage to property. It is typically used to describe substances and materials that are dangerous, including flammables, explosives, irritants, sensitizers, acids, and caustics, even when such materials may be relatively harmless in diluted concentrations.

What Is Hazardous?
A hazard is anything with the potential to cause harm. Risk is the probability of a negative outcome from exposure to a hazard. A substance is defined as hazardous if it has one or more of the following characteristics: flammable, corrosive, toxic, or reactive. Also, substances are defined as hazardous if they are specifically listed by regulation. For example, OSHA, EPA, and DOT publish lists of materials deemed hazardous.

In our discipline of occupational health and safety, the six primary hazard categories are:

  • Physical hazards
  • Chemical hazards
  • Biological hazards
  • Radiological hazards
  • Ergonomic hazards
  • Behavioral hazards

A physical hazard arises when use of a chemical is potentially dangerous due, for example, to the possibility of explosion, fire, or violent reaction with water. Peroxides, sulfuric acid, diethyl ether, and phosphorus pentachloride are examples of chemical materials that present physical hazards. Often, such materials also present health hazards due to their toxicity.

A chemical/substance is a health hazard if it produces acute or chronic health effects in exposed individuals. Materials that are health hazards include carcinogens, toxic or highly toxic agents, reproductive toxins, irritants, corrosives, sensitizers, hepatotoxins, nephrotoxins, neurotoxins, those which act on the hematopoietic system, and agents that damage the lungs, skin, eyes, or mucous membranes.

Consumer products are includable only if they are used in a manner not intended by the manufacturer. For example, PAM® cooking spray would not be included if it is used in normal food preparation. However, it would be included if it is used for coating metal smelting crucibles in a foundry operation. Insecticides, rodenticides, and pesticides are always included as hazardous by EPA regulation (FIFRA).

Biohazards are infectious agents or hazardous biological materials that present a risk or potential risk to the health of humans, animals, or the environment.

A biological hazard is one that is posed to humans by a biological organism or by a material produced by such an organism. The risk can be direct through infection or indirect through damage to the environment. Biohazardous materials include certain types of recombinant DNA; organisms and viruses infectious to humans, animals, or plants (e.g., parasites, viruses, bacteria, fungi, prions, rickettsia); and biologically active agents (i.e., toxins, allergens, venoms) that may cause disease in other living organisms or cause significant impact to the environment or community. They also can include CDC's "Select Agents," which are essentially biohazardous materials with terrorist/weapons potential.

A toxic substance is one that is capable of causing injury or damage to a living organism. A wide variety of materials are considered as toxic; examples are sulfuric acid, whose action is notably corrosive; compounds of heavy metals such as tetraethyl lead, which may act as systemic poisons; selenium compounds, such as selenium dioxide; and natural products, such as the aflatoxins.

The term toxicity denotes both the capacity to cause harm to a living organism and to indicate the adverse effects caused by a chemical. The degree of harm caused to an organism by exposure to a toxic chemical generally increases with exposure level, but it is also dependent upon the type of organism, the length of exposure, the physiological status of the organism (essentially its fitness), and its developmental stage. For example, some toxic chemicals have a more serious effect upon a developing fetus than upon an adult organism.

Hazard vs. Risk
We've defined hazard as the potential to cause harm; risk, on the other hand, is the likelihood of harm (in defined circumstances, and usually qualified by some statement of the severity of the harm).

The relationship between hazard and risk must be treated very cautiously. If all other factors are equal -- especially the exposures and the people subject to them -- then the risk is proportional to the hazard. However, all other factors are very rarely equal.

Consider the following examples:

1. Potassium dichromate is a highly toxic carcinogenic chemical used in some techniques to analyze exhaled breath for alcohol content. For this purpose it is sealed in a tube and does not become airborne. Therefore, although it is a highly hazardous substance, its use as described does not present significant risk to the user.

2. Flour is not generally considered to be a hazardous substance. A jar of it on a shelf would not have a skull and crossbones depicted on it, together with other hazard warnings, as might have been the case for a bottle of potassium dichromate. However, if a bakery worker were exposed over a period of time to airborne flour dust and/or dust by skin contact, s/he could develop dermatitis (an inflammation of the skin), conjunctivitis (inflammation of the eyes), rhinitis (information of the nose), and even occupational asthma, an inflammatory disease of the lungs that can cause a great deal of distress and may even be life threatening.

Thus, a material of relatively low hazard can present substantial risk, while a material with a high hazard might present no measurable risk in certain circumstances.

Public Health Hazard Categories
The Agency for Toxic Substances and Disease Registry (ATSDR) has established standardized categories for health hazards. Depending on the specific properties of the contaminant, the exposure situations, and the health status of individuals, a public health hazard may occur. Using data from public health assessments, sites are classified using one of the following public health hazard categories:

Category 1: Urgent Public Health Hazard: Conditions that pose a serious risk to the public's health as the result of short-term exposures to hazardous substances.
Category 2: Public Health Hazard: Conditions that pose a public health hazard as the result of long-term exposures to hazardous substances.
Category 3: Indeterminate Public Health Hazard: Conditions for which no conclusions about public health hazard can be made because data are lacking.
Category 4: No Apparent Public Health Hazard: Conditions where human exposure to contaminated media is occurring or has occurred in the past, but the exposure is below a level of health hazard.
Category 5: No Public Health Hazard: Conditions for which data indicate no current or past exposure or no potential for exposure, and therefore no health hazard.

Categorizing Risk
The characterization of risk has both quantitative and qualitative components to it.

It should be clear from the previous discussion that the type of hazard and the adverse outcome associated with it are important qualitative features of "risk." Thus, a specified probability of developing eczema dermatitis (an inflammation of the skin) would be considered a lesser "risk" than an identical probability of developing melanoma (a particularly severe form of skin cancer).

However, one needs to look more closely to be able to characterize "risk," as distinct from simply "hazard." The degree of exposure is an important determinant of risk. Thus, a low exposure to something that is highly hazardous may result in a low risk. Conversely, a high exposure to something of very low hazard may result in a moderate or even high risk. Every reasonable attempt must be made to quantify an exposure in order to then proceed to attribute a measure of risk to it. The probability of an adverse outcome (i.e., the likelihood of a certain risk) can be expressed in various ways.

Statements about causation often depend on certain assumptions. When an assumption about causation is wrong, then any associated measure of risk, however accurate numerically, can provide misleading information if it implies that the likelihood of a certain unwanted outcome (e.g., cancer, asthma) is specifically and undoubtedly caused by the stated exposure to a particular hazard. Therefore, statements about risk must be guided by indications of the uncertainty that may be associated with them.

One may wish to know what steps have contributed to a particular risk being so high and/or what steps can be taken to reduce the risk -- for example, to control the risks from occupational exposures. The cost of risk reduction measures and their benefits will need to be considered.

Perception of Risk
There can be vast differences in how risks are perceived by scientists on the one hand and by the lay public on the other. Several factors can influence this differential interpretation, including:

  • Personal experience of the adverse effect/event
  • Social cultural background and beliefs
  • The ability to exercise control over a particular risk
  • The extent to which information is gained from different sources (e.g., from the media and so on)
  • Other considerations (for example, it has been shown that people have a tendency to overestimate very low risk and sometimes to underestimate very high ones)

Risk Acceptance vs. Risk Aversion
Although the scientific community has a very important role to play in measuring risks and in presenting this information in as clear a manner as possible, with appropriate cautions about uncertainty, it remains a responsibility of society to determine what is tolerable and acceptable based on social, political, cultural, and even economic considerations.

Many hazards cannot be abolished in the sense that they are completely gotten rid of. Therefore, to reduce risk, more often than not it becomes a question of reducing exposure. In some countries, the goal for reducing occupational risks to health is to achieve a situation where "exposure should be controlled to a level to which nearly all the population could be exposed day after day, without adverse affects of health."

In future articles, we will discuss techniques and practices for identifying hazards, assessing the specific risks of such hazards, and using the findings to select and implement controls appropriate to reduce risk to acceptable levels in support of both safe and productive work outcomes.

This article originally appeared in the July 2011 issue of Occupational Health & Safety.

About the Author

D.C. Breeding, Ph.D., CSP, CHMM, is an EH&S professional practicing in College Station, Texas. He is director of Environmental Health, Safety & Security for the Engineering Program at Texas A&M University.

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