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3.2.2.: Classification criteria for substances

Substances shall be allocated to one of the following two categories within this hazard class:
(a) Category 1 (skin corrosion)

This category is further subdivided in three sub-categories (1A, 1B, 1C). Corrosive substances shall be classified in Category 1 where data is not sufficient for sub-categorisation. When data are sufficient, substances shall be classified in one of the three sub-categories 1A, 1B, or 1C (see Table 3.2.1.)
(b) Category 2 (skin irritation) (see Table 3.2.2).
3.2.2.1. Classification based on standard animal test data
3.2.2.1.1. Skin corrosion
3.2.2.1.1.1. A substance is corrosive to skin when it produces destruction of skin tissue, namely, visible necrosis through the epidermis and into the dermis in at least one tested animal after exposure for up to 4 hours.
3.2.2.1.1.2. Corrosive substances shall be classified in Category 1 where data is not sufficient for sub-categorisation.
3.2.2.1.1.3. When data are sufficient substances shall be classified in one of the three sub-categories 1A, 1B, or 1C in accordance with the criteria in Table 3.2.1.
3.2.2.1.1.4. Three sub-categories are provided within the corrosion category: sub-category 1A — where corrosive responses are noted following up to 3 minutes exposure and up to 1 hour observation; sub-category 1B — where corrosive responses are described following exposure greater than 3 minutes and up to 1 hour and observations up to 14 days; and sub-category 1C — where corrosive responses occur after exposures greater than 1 hour and up to 4 hours and observations up to 14 days.


Table 3.2.1

Skin corrosion category and sub-categories

Category

Criteria

Category 1 (1)

Destruction of skin tissue, namely, visible necrosis through the epidermis and into the dermis, in at least one tested animal after exposure ≤ 4 h

Sub-Category 1A

Corrosive responses in at least one animal following exposure ≤ 3 min during an observation period ≤ 1 h

Sub-Category 1B

Corrosive responses in at least one animal following exposure > 3 min and ≤ 1 h and observations ≤ 14 days

Sub-Category 1C

Corrosive responses in at least one animal after exposures > 1 h and ≤ 4 h and observations ≤ 14 days

(1)   See the conditions for the use of Category 1 in paragraph (a) of Section 3.2.2.
3.2.2.1.1.5. The use of human data is discussed in Sections 3.2.1.2 and 3.2.2.2 and also in Sections 1.1.1.3, 1.1.1.4 and 1.1.1.5.
3.2.2.1.2. Skin irritation
3.2.2.1.2.1. A substance is irritant to skin when it produces reversible damage to the skin following its application for up to 4 hours. The major criterion for the irritation category is that at least 2 of 3 tested animals have a mean score of ≥ 2,3 and ≤ 4,0.
3.2.2.1.2.2. A single irritation category (Category 2) is presented in Table 3.2.2, using the results of animal testing.
3.2.2.1.2.3. Reversibility of skin lesions is also considered in evaluating irritant responses. When inflammation persists to the end of the observation period in 2 or more test animals, taking into consideration alopecia (limited area), hyperkeratosis, hyperplasia and scaling, then a material shall be considered to be an irritant.
3.2.2.1.2.4. Animal irritant responses within a test can be variable, as they are with corrosion. A separate irritant criterion accommodates cases where there is a significant irritant response but less than the mean score criterion for a positive test. For example, a test material might be designated as an irritant if at least 1 of 3 tested animals shows a very elevated mean score throughout the study, including lesions persisting at the end of an observation period of normally 14 days. Other responses could also fulfil this criterion. However, it should be ascertained that the responses are the result of chemical exposure.


Table 3.2.2

Skin irritation category ()

Category

Criteria

Irritation (Category 2)

(1)  Mean score of ≥ 2,3 and ≤ 4,0 for erythema/eschar or for oedema in at least 2 of 3 tested animals from gradings at 24, 48 and 72 hours after patch removal or, if reactions are delayed, from grades on 3 consecutive days after the onset of skin reactions; or

(2)  Inflammation that persists to the end of the observation period normally 14 days in at least 2 animals, particularly taking into account alopecia (limited area), hyperkeratosis, hyperplasia, and scaling reactions; or

(3)  In some cases where there is pronounced variability of response among animals, with very definite positive effects related to chemical exposure in a single animal but less than the criteria above .

(1)   Grading criteria are understood as described in Regulation (EC) No 440/2008.
3.2.2.1.2.5. The use of human data is discussed in Sections 3.2.1.2 and 3.2.2.2 and also in Sections 1.1.1.3, 1.1.1.4 and 1.1.1.5.
3.2.2.2. Classification in a tiered approach
3.2.2.2.1.

A tiered approach to the evaluation of initial information shall be considered, where applicable, recognising that not all elements may be relevant.
3.2.2.2.2.

Existing human and animal data including information from single or repeated exposure shall be the first line of evaluation, as they give information directly relevant to effects on the skin.
3.2.2.2.3.

Acute dermal toxicity data may be used for classification. If a substance is highly toxic by the dermal route, a skin corrosion/irritation study is not practicable since the amount of test substance to be applied considerably exceeds the toxic dose and, consequently, results in the death of the animals. When observations are made of skin corrosion/irritation in acute toxicity studies and are observed up through the limit dose, these data may be used for classification, provided that the dilutions used and species tested are equivalent. Solid substances (powders) may become corrosive or irritant when moistened or in contact with moist skin or mucous membranes.
3.2.2.2.4.

In vitro alternatives that have been validated and accepted shall be used to make classification decisions.
3.2.2.2.5.

Likewise, pH extremes like ≤ 2 and ≥ 11,5 may indicate the potential to cause skin effects, especially when associated with significant acid/alkaline reserve (buffering capacity). Generally, such substances are expected to produce significant effects on the skin. In the absence of any other information, a substance is considered as corrosive to skin (Skin Corrosion Category 1) if it has a pH ≤ 2 or a pH ≥ 11,5. However, if consideration of acid/alkaline reserve suggests the substance may not be corrosive despite the low or high pH value, this needs to be confirmed by other data, preferably by data from an appropriate validated in vitro test.
3.2.2.2.6.

In some cases, sufficient information may be available from structurally related substances to make classification decisions.
3.2.2.2.7.

The tiered approach provides guidance on how to organize existing information on a substance and to make a weight of evidence decision about hazard assessment and hazard classification.

Although information might be gained from the evaluation of single parameters within a tier (see Section 3.2.2.2.1.), consideration shall be given to the totality of existing information and making an overall weight of evidence determination. This is especially true when there is conflict in information available on some parameters.