The threshold for subjective effects varies considerably from 0.1 to 2.5 ppm; most people feel symptoms in the throat first. According to OSHA odor threshold is 0.8-1 ppm.
The limit for airborne exposure to formaldehyde set by OSHA the Formaldehyde Standard (TWA) is 0.75 ppm in an 8-hour time-weighted average (officially 1 ppm) and 2 ppm for a 15-minute Short-Term Exposure Limit (OSHA STEL). By the way, in 1987 TWA was 3 ppm.
OSHA requires monitoring by the employer of the exposure to formaldehyde exceeds the 0.5 ppm (the Action Level) or the 2.00ppm STEL. A “representative employee” is asked to wear a sampling passive badge device to collect formaldehyde (industrial monitoring uses a different methodology). Determination time-weighted average (TWA) collected from the employee’s breathing zone air during full shift is considered as optimal. Usually monitoring is done on annual basis. The badges are portable, for example provided by Advanced Chemical Sensors, Inc. www.acsbadge.com. They meet the OSHA standards.
The American Conference of Governmental Industrial Hygienists (ACGIH) has more stricter requirements for time weighted average (TWA) short-term-exposure limit (STEL) (0.3 ppm) than OSHA (2 ppm), although the recommended exposure limits do not have a legal application in the USA in opposite to OSHA. It is remarkable that the ACGIH 0.3 ppm limit is set on irritation, not carcinogenicity. I my opinion, ACGIH limits are not attainable in the surgical pathology laboratory. Actually, they are not necessary to use in laboratory practice, although they are reasonable in industrial setting because there might be additional factors which can be combined with formaldehyde (industrial dust, metallic particles, etc.). The most important is that surgical pathology handles 10% Formalin, but not formaldehyde as emanating gas.
Two personal stories reflect the relative value of this monitoring.
Being “soaked” by formalin for many years, my annual monitoring had never reviled any abnormal reading. I left once by accident a monitoring badge overnight on my coat near buckets with formalin, but somebody for some reasons open the lid. I do not have any explanation why the reading came normal. I always resisted temptation to repeat intentionally this “experiment.” I haven’t done this for good reasons that show the second story.
Recently, during annual monitoring, personal samples at two grossing stations collected on the same day near each other came back with different readings. One was 10 ppm while another showed 0.055 ppm. Nobody on this day reported any odors that would be consistent with high formaldehyde exposures. It was a simple explanation as splashing that could contaminate the sample badge, but the management became so agitated that a special consulting firm was invited, with many days of monitoring performances, meetings, and papers. Nobody wants to take chances to deal with the regulatory governmental institutions. Unfortunately the right idea of formaldehyde exposure monitoring collides with fear that is not the best adviser to common sense.
Usually histology laboratories use a passive badge monitor containing bisulfite-impragnated paper with chromotropic acid analysis with TWA validation range from 0.2 to 4.9 ppm and overall error +/_ 18.6%.
Annual monitoring is mandatory, but during the year many events might occur with disruption of ventilation system and other violations of formalin handling. An established monitoring system, that includes passive monitoring, hood vaneometers, filtering system, hand held formalin monitors, even oximeter, might be beneficial (Rene Buesa personal communication).
Perhaps in addition, it is reasonable to have quantity monitors on a regular basis, like canaries in the old coal mines for methane and carbon monoxide overconcentration detection. Some reagents like well known in histology laboratory Schiff reagent (red)) or reticulin diamine silver solution (black) in contact with aldehydes can provide a warning that will alert that there are some signs of formaldehyde overexposure at different areas of the histology laboratory. The bisulfate indicator that is a reagent in the standard monitor badge might be used for quantity monitoring. I am using this opportunity to challenge manufacturers in developing such quantity monitors. The market can be sufficient for a commercial return investment for the development of such device. Meanwhile, a Schiff reagent would be useful to have handy in every surgical pathology laboratory to prevent from sniffing containers with formalin in question. This popular habit is obviously unhealthy.