Formaldehyde can be irritating to the eyes and nose this is called sensory irritation. Sensory irritation is caused by the chemical stimulation of the tregeminal nerve in the nose. This results in a stinging or burning sensation. The level that this occurs is difficult to measure because the effect is very subjective much like the detection of an odour which uses stimulation of the same nerves.
While some agencies have used a level as low as 0.1 ppm as a threshold for irritation, an expert panel found that a level of 0.3 ppm would protect against nearly all irritation. In fact, the expert panel found that a level of 1.0 ppm would avoid eye irritation -- the most sensitive endpoint -- in 75-95% of all people exposed (Paustenbach).
It should be noted that this effect is different from skin irritation or corrosivity used for hazard classification, which are based on physical damage to the cells whereas sensory irritation is a nerve response.
The effect is immediately reversible. If the source of formaldehyde is removed the effect ceases immediately. Because of the strong odour of formaldehyde the user is protected
NICNAS makes the following comment regarding the risk of sensory irritation to the general public.
“The risk of sensory irritation to the public is also low based on the comparison of the NICNAS proposed ambient air standard (80 ppb, see Recommendation 17) and the estimated formaldehyde levels in ambient air.”
Sensory irritation is also different to Asthma. NICNAS made the following comments on Asthma related to formaldehyde exposure.
“Furthermore, although asthmatics are thought to be more sensitive to irritants, studies by Green et al. (1987), Sauder et al. (1986; 1987) and Witek et al. (1987) have demonstrated that at concentrations of 2 - 3 ppm (2.4 - 3.6 mg/m3) for up to 3 hours, asthmatics were no more sensitive to formaldehyde than nonasthmatics.”
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