Step 1: Hazard Identification - identify the hazard

Hazard identification is based on literature review and in hazard identification, we identify what health effects will result for humans from a given exposure. For example, if we want to conduct a hazard identification for something like a wood burner in the house, we would have to review what health effects will result from burning wood inside a house would result. This could be based on reviews of outdoor air pollution and associated health effects in winter, or health effects of burning wood inside the house and indoor air pollution that results from this activity and associated health effects. As this is a desktop exercise, we conduct hazard identification by conducting a review of the toxicological, and epidemiological literature. A toxicological literature review basically means that we review animal experiment data and data from studies on human tissue based samples and studies on health effects. Epidemiological literature are based on human health outcomes. When we conduct such literature review, we must pay attention to the following features:
  1. The quality of the review
  2. The specific exposure or the mixture of the exposure variables
  3. The health outcome studied
  4. If an animal model is studied, how does that animal model relate to the humans?
  5. What are the toxicological mechanisms?
  6. What are the potential human routes of exposure? Some exposures are through inhalation; others are through ingestion; how are they comparable with human studies?
  7. Is it possible to extrapolate quantitative dose response studies?
According to the California Environmental Protection Agency, occupational epidemiological studies are limited because the studies are conducted for healthy adults, and excludes children and older adults who are outside of workforce age \cite{Agency:2010rm}. Animal studies are of limited use too unless the animal models are similar to humans or unless animal diseases or health states can be replicated in humans. Epidemiological studies also suffer from limited range of exposure and limited number of people on whom these studies are conducted. Therefore, while no study is foolproof, we need to use caution and a checklist to check the limitations and usefulness of specific types of studies. What health effects shall we study? In general, we should focus on one particular health effect, even if a number of different health effects are listed. So, for example, when we are studying indoor radon gas, a gas often given off in places where uranium mines are located and found in basements of the houses, we should look for one particular health effect -- generally the one that occurs that occurs frequently or something that is significant. The word significant can be misleading here as what is significant to one group of people may not be significant to the others. In general, cancers such as lung cancer in case of radon gas exposure would be considered as an important health outcome to focus on. Another way to look for health effect is to focus on what is the most sensitive health effect and occurs at low doses of exposure or critical, a health effect that is so important that it must be addressed as it affects a large number of people who live in the environment where such exposures occur.
In summary, what information do we need at this stage of EHRA?
Several databases of the toxins exist, and the ones that are frequently used are (1) "Technical Fact sheets" put up by the United States Environmental Protection Agencies (see the website: https://www.epa.gov/sites/production/files/2014-03/documents/ffrrofactsheet_contaminant_perchlorate_january2014_final_0.pdf) for more information on PBDE; (2)  Another site from where you can find more information about toxins is the ATSDR website, see here: https://www.atsdr.cdc.gov/. Both these sites will provide you with sufficient information as to the toxins: what they are, their chemical or physical properties, their modes of action, animal and human studies so that you can embark on the next step: exposure assessment.
What if you cannot obtain the needed information from these sources? In such situations, you will need to rely on individual studies on chemical properties, animal studies, epidemiological studies, and so forth. So, in case  you need more information or when information is not found in ATSDR or the Fact Sheets, do:
You may find that often nothing is known. In such situation, an EHRA is perhaps not the best thing to do. Insead, when you know nothing at all and all you have are health effects or diseases that you face, your only way is to conduct an epidemiological study or set up a surveillance system and study the physical or chemical properties of the toxin, conduct animal experiments, and try to put together these knowledge to conduct a local health risk assessment. 

Step 2: Exposure Assessment -- assess how much the community is exposed and the dose