Risk Assessment: Background

Risk assessment is an important concept that is applicable to our lives. We do it every day when we are exposed to a hazard such as a wet floor, chemical spill, or spoiled food. Because hazards affect us every day, it is important to consider how we assess risks in our lives and how government agencies evaluate risks. Government agencies similarly evaluate risks, but applying a more formal process. Our own process of assess risks can help us understand how government agencies establish health, safety, and environmental standards (legal limit) as well as the recommendations when there is insufficient information to establish a standard that is enforceable.

Hazard, Risk, and Safety: To begin to understand risk assessment it is important to understand what is a hazard, what is risk, and what is meant by safety? A hazard is anything that has the ability to cause harm and therefore may pose a threat that can negatively affect a person or the environment (e.g., a wet floor is a hazard). Within the context of this module, environmental hazards can include both physical hazards (factors around us that can cause harm, such as a spill on a floor or a constant loud noise) and chemical hazards (harmful chemical in any form, such as cleaning products or asbestos). Risk is the probability that a harmful event will occur and the amount or severity of harm from that event (the probability and consequences of slipping on the wet floor define the risk). Another way of thinking about risk is the probability that a hazard can affect a person or the environment and the consequence of that hazardous event occurring. If the probability is low and/or the potential effects are mild, then the risk is low; if the probability is high and/or the potential effects are serious, then the risk is high. Without a hazard there is no risk and with every hazard there will always be some degree of risk (Table 1). Safety involves making a judgment about whether the risk is low enough to be considered safe or is too high to be considered dangerous. The judgment about safety can be personal, or made by a governmental agency, and can vary from one person (or agency) to another.

Table 1: Examples of hazards and risks in our daily lives:
What is the probability that my son or daughter will get sick with the flu if he/she is in contact with other children that are sick with the flu in school?Flu from other children sick at schoolThe likelihood that my son or daughter will get sick and the severity of that sickness
What is the probability that I will fall down stairs that do not have a banister?Stairs without a banisterThe likelihood and amount of injury from falling down stairs

How can we know if there is something around us that represents a risk? The first step is to find out whether it is harmful and can affect our health (hazard can impact us). There are five key questions that can help us find out if the hazard represents a risk. The questions that we should ask ourselves are:

  • Is there a hazard (is there the potential for something harmful to happen)?
  • Are we exposed to the hazard?
  • What is the risk associated with that exposure?
  • What is the likelihood of that hazardous event happening?
  • What are the consequences and how much harm may occur if that hazardous event happens?

These questions address the possibility of harm. This is where we must ask what are the consequences to health or well-being, or if it could even cause death. Understanding the consequences of that risk should inform the risk management process.

There are different ways to identify a hazard and its potential effect. A simple example would be the identification of mold (e.g., black mold) in a home. This mold can be found under the sink, in the kitchen, or in the bathroom tub. At the same time, you can identify the cause of the mold such as the presence of a leak or lack of ventilation.  The mold is a hazard because exposure to mold can affect one’s health. The risk is determined by how much exposure occurs (is there a lot of mold and is it in a location where family comes in contact?) and how severe are the health effects (does the mold cause mild irritation or fever and shortness of breath or how sensitive are family members?). 

Similarly, contaminants can be detected in the drinking water of a community through water quality testing (monitoring of water quality). These contaminants can be found in groundwater that is used to supply homes with drinking water. The source of the contaminants can be identified as a factory or landfill that is leaching the contaminants. The contaminants are a hazard because drinking contaminated water can affect one’s health. The risk is determined by which contaminants are present, at what concentrations, how much are people drinking, and are the health effects mild or serious.

In both examples, the hazards (mold and contaminant) may affect the health of people and the environment, therefore it is important to identify the potential risks in order to take precautions and to protect the exposed population. We can discover what are the risks associated with hazards in several ways. For chemicals, scientists study animal models (in vivo or animal testing). Unfortunately, we also learn from situations where people have been exposed to high levels of contaminants (case studies or epidemiological studies).

Remember, risk is the probability that a person or a group of people will be harmed by a hazard. Risk assessment is a process by which we understand and identify hazards and calculate or determine the likelihood (probability) and severity of that hazardous event occurring. We assess risks every day, often without realizing it. Our everyday risk assessment is used to inform our personal judgment to determine if and how we can be affected by hazards that are around us, in workplaces, public areas and even in our own homes. We assess our risks and then decide on the actions we will take. This all depends on the degree of harm that the hazard represents. The degree of risk may be based on how you were exposed (e.g., skin, ingested, or inhaled), the amount and concentration, and the length of time of the exposure.

Government Risk Assessment:  We are not the only ones concerned about risks from the hazards that surround us. Several government agencies carry out risk assessments within various contexts to protect the general population (Table 2).

Table 2. Governmental agencies that are in charge of measuring risk.
Agency Name and AcronymThis agency is in charge of…
US Food and Drug Administration (FDA)providing safe food to consumers, in addition to determining what medical drugs can be sold in the United States market
Occupational Safety and Health Administration (OSHA)protecting the health of workers
Agency for Toxic Substances and Disease Registry (ATSDR)preventing harmful exposures and diseases related to toxic substances
US Environmental Protection Agency (US EPA)safeguarding the environment and people’s health

The risk assessment that these agencies implement is a formalized process that is based on toxicology (the study of the effects of chemicals on health), epidemiology (the study of disease occurrence in humans), economics, and social factors. In general, the process focuses on estimating the probability that a harmful event will occur and the likely magnitude of the adverse effects. During this formalized risk assessment, all of the available information on the effects and associated risks of a chemical substance is collected. Government agencies use information from epidemiological and toxicological investigations. Also, these agencies conduct their own internal investigations to add to the body of knowledge.

Government agencies use risk assessment to identify which risks need to be controlled by preventive measures, remediation efforts, allocate resources, procedure changes, and control measures. Using the information gathered through a risk assessment process, government agencies can set permissible exposure limits (sufficient scientific evidence of significant harm to the population is concluded, therefore the government can issue a standard which is enforceable by law) for chemical substances as well as give human health guidelines (issued by governmental or non-governmental organizations, but not generally enforceable by law). The decisions made by government agencies that use the risk assessment process not only happen once, but this process is continually updated to incorporate new information once it is available (this can be a slow updating process at times). Generally, the formal risk assessment process includes four main steps, which are the following (Table 3):

Table 3. Summary of the steps carried out in the risk assessment process.
Hazard IdentificationInvolves the collection of data to determine which contaminants are present, where they are present, at what concentrations, and what types of health effects they are capable of causing
Dose-Response EvaluationThe purpose of this step is to calculate the dose (amount of human exposure) at which an adverse effects can be observed
Exposure AssessmentThe potentially affected or vulnerable populations and routes of exposure are identified in order to calculate the amount of exposure, based on the frequency, duration, and the amount of contact with the contaminant
Risk CharacterizationAll the information that is obtained from the above steps is combined to determine the actual risk of exposure to the hazardous substance

The dose-response evaluation step of the risk assessment process is very important because it documents the relationship between the amount of a hazard that people are exposed to and the effect at different exposure levels. In other words, dose-response measures the amount (dose) that causes a certain adverse effect (response). Typically, this comparison is used in the development of a formal risk assessment on a chemical substance. The more you are exposed to the hazard, the more your health is at risk.

To better understand dose-response we will graph it for the consumption of chili peppers (Figure 1). If a person eats one jalapeño pepper they will have a slight reaction to it, if this person then eats three jalapeño peppers they are going to feel the spiciness, and if they have six jalapeño peppers their mouth will be burning. Similarly, this happens with a chemical substance. If you consume a small amount of the chemical maybe nothing happens but if you triple the dose the reaction will be more severe. It is also important to note that some chemicals substances might cause severe health effects in small quantities or different responses will occur depending on the person exposed. Using the example of the chili peppers, you might only need a small amount of a certain type of chili (habanero) to have a major effect or some people do not have a tolerance to chili peppers while other do have a tolerance and can eat many chili peppers without any having negative effects.

When it comes to pollutants or chemical substances that may have an effect on human health, knowledge of these effects are important for individuals or communities that are impacted by them. The US EPA, ATSDR, OSHA, and most state health and environmental agencies divide the effects into two types: 1) carcinogen is a chemical that causes cancer or 2) noncarcinogen is a chemical that causes other types of health effects (e.g., effects on internal organs, reproduction system, or the developing fetus). This is an important distinction because a carcinogen is regulated more strictly (exposures are controlled to much lower acceptable levels), which is significantly more costly.

A carcinogen is treated as something that could lead to the development of cancer, even at low exposures. Typically, the chemical has no zero risk level, but at some low exposure level the risk is so low as to be considered safe. To label a chemical as carcinogenic is complicated because it can take many years/decades to find the evidence needed to establish with certainty that it does cause cancer. Once a chemical is identified as a carcinogen, it is assumed that there is always a possibility of risk and it increases with the dose and the exposure time. In contrast, for many noncarcinogens there is a low level of exposure that effects the health of a person in other ways (e.g., skin rashes, heart problems, and development of diabetes). Actually, not all substances can cause cancer, regardless of how high the dose and how long the exposure time, it also depends on the chemical and other personal characteristics (e.g., genetics, gender, and age).

Probability, Uncertainty and Variability: When we go through the risk assessment process it is useful to consider other concepts such as probability, uncertainty, and variability. These concepts are important in determining how strong the risk assessment process can determine what happens in reality. Risks are not always the same for everybody and every situation. Our knowledge of hazards and how they affect people can also be incomplete. Probability, uncertainty, and variability can be found in every step of risk assessment.         

Probability is the likelihood that a certain result will occur. Risk is essentially probability. In terms of risk assessment, it is a measure of how likely an adverse effect will occur from an exposure. Probability can be defined in terms of time, an event, a population, an activity, etc. For example, what is the probability of winning the state lottery (1 in 175,223,510) or dying from a stroke (1 in 29)? Table 4 contains other examples of the probability of different risks.

Uncertainty in the process of risk assessment involves the lack of precise knowledge. In risk assessment much of our knowledge about the adverse effects of chemicals on the human body come from animal studies and there is some uncertainty about whether humans will be affected the same as the animals. There is often also uncertainty about the exact level of exposure for all individuals in an affected population. A risk assessment often makes assumptions about how humans respond to chemicals and how much human exposure occurs in the population; these assumptions may not be accurate for all people who are exposed. For example, when assessing the risks of lead exposure, there may be uncertainty about blood lead concentrations in an exposed population or the total amount of daily lead exposure in that population. When a risk assessment is carried out an amount of lead in blood will have to be used which is representative of the entire population exposed to calculate the risk (to calculate the risk for each individual in a population exposed would take a lot of time and money). As the amount of lead that is calculated does not exactly match all the individuals of a population, here is were uncertainty is introduced into the risk assessment process. In other words, since you have to make an assumption regarding the amount of blood lead, there will be individuals in the population who have more blood lead and/or daily exposure and others who will have less blood lead/exposure than the value that was chosen for the risk assessment calculation. The following table presents more practical examples (Table 4).

Table 4. Examples of risks and their respective probability and uncertainty (adapted from Environmental Health (3rd Edition) by Dade W. Moeller). *Data availability, how the study was conducted, and etc. may contribute to the uncertainty.
RiskProbability of this riskUncertainty*
Death before age 85 (all causes)70%Low
Death due to cancer (lifetime)25%Low
Death by cigarette smoking (1 pack per day through 40 years)13%Medium
Death by car accident (lifetime)2%Low

Variability is very much different from the concept of uncertainty although they are often confused. Variability within the framework of risk assessment refers to the differences between individuals in a population in how a contaminant affects their health and how much exposure they have to that chemical. Variability produces differences in exposure over time and health effects among the various affected people. To clarify the idea of variability the following table provides some practical examples (Table 5).

Table 5. Practical examples of variability.
Not all people who smoke cigarettes develop cancer
Women are more likely to develop breast cancer than men
You drank three cups of coffee today, but only a single cup yesterday
An adult will have a different reaction to a chemical compared to a six year old boy

We are not all the same therefore the dose of a substance affects us in different ways. Often exposure to other hazards (e.g., cigarettes) may increase the risk as well as the development of certain health problems. Sometimes, it is difficult to distinguish between variability and uncertainty, so to give you a better idea the following are more detailed examples in the context of risk assessment:

Example: Lead

Lead is a metal that affects the long-term health of humans because it causes problems that do not necessarily develop overnight. It has a greater effect on vulnerable populations such as children and the elderly. It is important to know that no amount of lead is safe and because of this we have to be aware of its different sources. Some of these sources include paint in a house that was built before 1978, certain types of pottery and glass used for cooking/storage (the glaze may contain lead or the glass was made ​​with lead), certain candies produced in other countries (e.g., Mexico), and solder typically found in old plumbing such as cast iron (when lead-based solder wears, lead particles are transported in the drinking water). The health effects that may develop include slow mental and physical development, anemia, and stomach problems. Determining the risk of lead exposure may include an assessment of the home taking into account certain characteristics as well as probable sources. Measuring lead in a person’s blood is one way of determining the level of exposure of a person. In assessing the risk, there will be variability in exposure to lead a population given that there are various characteristics of the household as well as the personal characteristics and behaviors of this population. At the same time, there will be uncertainty in quantifying the effects of lead exposure because they cannot accurately account for factors such as genetics, lifestyle, and exposure to other chemicals.

What can we do?

To reduce exposure to lead the possible sources need to be reduced. It is important to wash hands frequently and clean toys that are in contact with soil. Stay informed about recalls regarding toys or candy containing lead. If you live in a house built before 1978, keep the paint in good condition. Keeping it in good condition helps contain any lead-based paint. If you remodel your home, you should take a sample of the wall and paint that will be part of the remodeling effort. If samples indicate that the wall or paint containing lead it is a good idea to hire an expert contractor that is certified in lead abatement who can take precautions to reduce exposure. Consider using cold tap water for drinking and cooking. If you have not used the tap water for more than six hours, you should let the water run for a minute or two before using it. Also, if someone in your household works in a place where he/she comes into contact with lead it is recommended that they change clothes and shoes before entering the home. It is likewise recommended to wash their work clothes separately.

Children under age six should have their blood analyzed for lead. If the level of lead in the child's blood is higher than that recommended by the Centers for Disease Control and Prevention (5 micrograms per deciliter of lead in blood), the Department of Health Services Arizona or local health services should work with the family to identify the source of lead and how they can reduce their exposure to the lead.

Example: Falls

The act of falling is an involuntary loss of balance that allows the human body to make contact with the ground or other surfaces. Falls are a hazard that is present in our daily lives. Vulnerable populations such as children and the elderly tend to be at higher risk for falling and being harmed as a result. Many times we do not think anything is going to happen to children because they are small, but because their bodies are still developing they are at risk of having more serious consequences, similar to the elderly. Falls may cause serious injuries, minor shock, or even death. It is important to prevent falls because the effects are often internal and cannot be seen readily. When assessing the risk of a fall, we should note the area of ​​interest and identify places where people can trip, slip, and fall. There will be variability in the number of times those individuals in a population passing through the area of ​​interest, which might have a history of falls. Also, there is uncertainty in that each person can have different effects of the fall that are related to genetics, lifestyle, or health condition.

What can we do?

Remove all toys or other objects that can be considered a hazard from a pathway. Install handrails in places that have stairs or balconies. Also, use non-slip mats in bathtubs or slippery areas such as entrance areas and/or stairs. Also, wear shoes that fit well and have non-slip soles to prevent falls. It is always important to illuminate areas where people frequent at nighttime. It is recommended that if a liquid spills onto the floor, it should be cleaned immediately to prevent slips or fall. Avoid drinking too much alcohol or taking medication that may affect your balance. Muscle strengthening and balance exercises can help prevent falls. It is also recommend having yearly checkups regarding your general health as well as your musculoskeletal function.

If a person falls, do not pick them up quickly. First, you should check if they are conscious or dizzy/sick. If the person cannot get up by himself or herself, you should ask for help from someone else to help you get them up. Similarly, if you witness a severe fall do not move the person and immediately call 911 for medical assistance.


Animal testing – refers to studies that are tested on animals.

Carcinogen – something that is directly associated with causing cancer.

Case studies – research studies based on a real-life situation where data can be obtained.

Chemical Hazard – chemical (liquid, solid, or gas) substances that may cause harm.

Dose-Response – describes the changes caused by different levels of exposure (doses) to something (usually a chemical) after a certain time period.

Economics – social science field that studies economic activities and the impact on diverse areas of our society.

Epidemiological studies – area of science that studies the patterns of disease or health effects in a specific population.

Epidemiology – science area that studies the incidences and controls of diseases or health effects on a defined population.

Hazard – substance, situation, or object that is considered a source of danger.

Human Health Guidelines – recommendations that are not enforceable but are suggested in order to guide government agencies and the public.

In vivo – refers to studies that are tested on living organisms.

Noncarcinogen – something that is not associated with causing cancer, but may cause other effects.

Permissible Exposure Limits – legal limits in the United States that are set to protect from chemical and physical hazards.

Physical Hazards – factors in the environment that can physically harm (can also harm within out touching).

Probability – helps us to understand what might happen.

Remediation – the action of cleaning-up or stopping an environmental impact.

Risk – the possibility that something bad will happen.

Risk Assessment – process that determines the value of risk related to a situation, substance, or recognized threat.

Safety – the state of being “safe” from harm.

Social Factors – characteristics that influences a person’s experience, personality, attitude, and lifestyle. 

Toxicology – scientific area that studies the adverse effects of chemical substances on organisms.

Variability – the state of being different or changing. 

Uncertainty – a lack of certainty due to limited knowledge or exact knowledge.