1. For the purposes of paragraph 26(b) and 29(c) of these Regulations, a substance or mixture of substances is excessively irritant if it is excessively irritant to the eye or the skin, when judged on human experience or when based on the test method set out in this Schedule.
Method for Testing Eye Irritant Properties
2. (1) Use six albino rabbits for each test substance. Ensure that animal facilities for such procedures are designed and maintained so as to exclude sawdust, wood chips or other extraneous materials that might produce eye irritation. Examine both eyes of each rabbit before testing. Use only those rabbits without eye defects or irritation. Hold the rabbit firmly but gently until quiet. Place the test substance in one eye of each rabbit by gently pulling the lower lid away from the eyeball to form a cup into which the test substance is dropped. Gently hold the lids together for one second and then release the rabbit. The other eye, remaining untreated, serves as a control. For testing liquids, use 0.1 mL (2 drops) of the test substance. For testing solids or pastes, use 100 mg (1.5 grains) of the substance. For substances in flake, granule, powder or other particulate form, use the amount that has a volume of 0.1 mL (2 drops) (after compacting as much as possible without crushing or altering the individual particles, such as by tapping the measuring container) whenever this volume weighs less than 100 mg (1.5 grains). In such a case, record the weight of the 0.1 mL (2 drops) test dose. Do not wash the eyes after instillation of the test substance except as noted in subsection (2).
(2) Examine the eyes and record the grade of ocular reaction at 24, 48 and 72 hours. Use a binocular loupe, hand-held slit-lamp or other expert means to facilitate observing the reactions. After recording the observations at 24 hours, the eyes may be further examined after fluorescein is applied. For this optional test, drop 0.05 mL (one drop) of fluorescein sodium ophthalmic solution U.S.P. or equivalent directly on the cornea. After flushing out the excess fluorescein with sodium chloride solution U.S.P. or equivalent, injured areas of the cornea appear yellow. This is best visualized in a darkened room under ultraviolet illumination. The eyes may be washed with sodium chloride solution U.S.P. or equivalent after the 24-hour recording.
(3) A rabbit is considered to exhibit an excessive reaction if, at any of the observations, the test substance has produced one or more of the following reactions:
(a) an ulceration of the cornea, other than a fine stippling;
(b) an opacity of the cornea, other than a slight dulling of the normal luster;
(c) an inflammation of the iris, other than a slight deepening of the folds (or rugae) or a slight circumcorneal injection of the blood vessels; or
(d) an obvious swelling in the conjunctivae (excluding the cornea and iris) with partial eversion of the lids or a diffuse crimson-red with individual vessels that are not easily discernible.
(4) The test is positive if four or more of the rabbits in the test group exhibit a positive reaction. If only one rabbit exhibits a positive reaction, the test is considered negative. If two or three rabbits exhibit a positive reaction, repeat the test using a different group of six rabbits. The second test is positive if three or more of the rabbits exhibit a positive reaction. If only one or two rabbits in the second test exhibit a positive reaction, repeat the test with a different group of six rabbits. If a third test is needed, the substance is excessively irritant if any rabbit exhibits a positive response.
(5) The publication Illustrated Guide for Grading Eye Irritation by Hazardous Substances is sold by the Superintendent of Documents, Government Printing Office, Washington, D.C., U.S.A. and may assist testing laboratories and other interested persons to interpret the results obtained when a substance is tested in accordance with subsection (1). The guide contains colour plates depicting responses of varying intensity to specific test substances. The grade of response and the substance used to produce the response are indicated.
Method for Testing Skin Irritant Properties
3. (1) Measure primary irritation to the skin by a patch-test technique on the abraded and intact skin of an albino rabbit clipped free of hair. Use a minimum of six rabbits. Introduce the test substance — 0.5 mL (10 drops) in the case of liquids or 0.5 g (7-8 grains) in the case of solids or semisolids — under a square patch that is made up of two single layers of surgical gauze measuring 25 mm by 25 mm (1 inch by 1 inch). Dissolve solids in an appropriate solvent and apply the solution as in the case for liquids. Immobilize the rabbits and secure the patches in place with adhesive tape. Wrap the entire trunk of the rabbit with an impervious material such as rubberized cloth for the 24-hour period of exposure. This material aids in maintaining the test patches in position and retards the evaporation of volatile substances. After 24 hours of exposure, remove the patches and evaluate the resulting reactions on the basis of the designated values in the following table:
Item Evaluation of skin reactions ValueFootnote for1 1. Erythema and eschar formation (a) No erythema 0 (b) Very slight erythema (barely perceptible) 1 (c) Well-defined erythema 2 (d) Moderate to severe erythema 3 (e) Severe erythema (beet redness) to slight eschar formation (injuries in depth) 4 2. Edema formation (a) No edema 0 (b) Very slight edema (barely perceptible) 1 (c) Slight edema (edges of area well defined by definite raising) 2 (d) Moderate edema (raised approximately 1 mm (0.04 inch) 3 (e) Severe edema (raised more than 1 mm (0.04 inch) and extending beyond the area of exposure) 4
Return to footnote 1The “value” recorded for each observation is the average value of the six or more rabbits subject to the test.
Repeat the observations at the end of a total of 72 hours (48 hours after the first observation). Make an equal number of exposures on areas of skin that have been previously abraded. Ensure that the abrasions are minor incisions through the stratum corneum (horny layer of the epidermis), but not sufficiently deep so as to disturb the derma or to produce bleeding. Evaluate the reactions of the abraded skin at 24 hours and 72 hours, as set out in this subsection. Add the values for erythema and eschar formation at 24 hours and at 72 hours for intact skin to the values on abraded skin at 24 hours and at 72 hours (four values). Similarly, add the values for edema formation at 24 hours and at 72 hours for intact and abraded skin (four values). Divide the total of the eight values by four to give the primary irritation score. A score of five or more indicates that the substance is excessively irritant.
(2) For the purposes of paragraphs 26(b) and 29(c) of these Regulations, a substance is excessively corrosive if it causes visible destruction or irreversible changes in tissue at the site of the application.
4. For the purposes of paragraphs 26(b) and 29(c) of these Regulations, a substance is an excessively strong sensitizer if it causes an allergenic sensitization in a substantial number of persons who come into contact with it.
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