Editors Present New Edition of AIHA Odor Threshold Publication

By Abby Roberts

Since the first edition of AIHA’s Odor Thresholds for Chemicals was published in 1989, this resource has guided occupational and environmental health and safety professionals in using odor detection to evaluate occupational health and safety hazards. The fourth edition of this document was published May 10, 2024. In an educational session given at AIHA Connect 2024 on May 21, the editors of this new edition outlined major differences between its contents and those of previous versions. These changes, such as the removal of predictive odor thresholds, aim to better represent varying odor detection abilities and to provide practitioners with data while allowing them more latitude to make decisions.

“There is no such thing as a perfect nose,” said Alex Lehocky, MS, CIH, one member of the editorial team, during his introductory remarks. A person’s sense of smell is influenced by many factors, including age, gender, and genetics.

Another editor, Cheri Marcham, PhD, CIH, CSP, CHMM, FAIHA, outlined terminology related to odor detection abilities. Normosmia is the technical term for a normal sense of smell, while anosmia refers to a permanent, temporary, or transitory, total or partial loss of smell. Many people may also have hyposmia (reduced sense of smell), hyperosmia (heightened sense of smell), parosmia (distorted sense of smell), or phantosmia (sensation of smell where none exists). Marcham related how her own ability to sense odors has been reduced since she contracted COVID-19 three years ago. For example, bleach, alcohol, and gasoline all smell the same to her now—but not like she had perceived them before her illness. She will also occasionally perceive the odor of a cigarette burning when there isn’t one nearby.

Marcham also explained that humans have different thresholds for detecting, recognizing, and being irritated by odors. The detection threshold is the point at which a person with “normal” sense of smell would detect an odor’s presence 50 percent of the time; the recognition threshold is when this person correctly identifies the odor they’re smelling 50 percent of the time, requiring them to be familiar with it. The irritation threshold is the point at which their trigeminal nerve is triggered.

Editor John Krause, PhD, MSPH, CIH, FAIHA, then took over to discuss the differences between the brain’s olfactory nerve, which perceives odor, and the trigeminal nerve, which perceives irritation. The concentration of a substance at which a person senses an odor is not the same concentration at which they are irritated by it, he explained, although some hazardous chemicals have a very low range between detection and irritation.

Marcham then returned to discuss the impact of viral infections on a person’s sense of smell. The SARS-CoV-19 virus is widely associated with loss of smell, but rhinoviruses, influenza, parainfluenza, and Epstein-Barr virus may alco cause post-viral olfactory dysfunction. Patrick Owens, CIH, CSP, the fourth member of the editorial team, then elaborated on factors affecting odor detection. For example, pregnant people and “trained” panelists in odor studies may be more sensitive to odors. Older people, smokers, and people with cumulative exposure to an odor were among groups with higher thresholds of detection. A person’s ability to detect or recognize odors could even vary depending on whether they had just eaten, the time of day, and on visual input.

Owens also cautioned participants to be wary of some of the outdated references in older editions of Odor Thresholds. “If you take anything away from this,” he said, “you need to look carefully at the source values and the study.” He also briefly discussed some of the improved testing methods outlined in the new publication, including a device that prevented odor study panelists from inhaling too quickly, which would dilute the odor.

The presenters distributed a simple odor test to people who attended the session in person. Each participant received a test packet, scratched the covering off the sample, and reported what they smelled through an online poll. Most, but not all, participants correctly detected the smells of peanuts, mint, and paint thinner.

Odor perception should not be used to trigger controls, Owens warned. A chemical is considered to have poor warning properties if the odor, taste, or irritation effect is not detectable below the OEL, he said. And OEHS professionals should not require workers to change respirator cartridges when they detect an odor.

At the end of the session, Lehocky shared potential directions for future research, such as exploring irritancy values and odor thresholds for mixtures. The fourth edition of Odor Thresholds for Chemicals is available for purchase from AIHA’s online marketplace.

Abby Roberts is the assistant editor for The Synergist.

Read more coverage of AIHA Connect 2024.