歐盟的危險性符號的定義

如果閣下能夠理解英文的話，以下為歐洲聯盟理事會在 1967/06/27 的議決內容（摘錄）：

2. The following substances and preparations are "dangerous" within the meaning of this Directive: (a) explosive:

substances and preparations which may explode under the effect of flame or which are more sensitive to shocks or friction than dinitrobenzene;

(b) oxidising:

substances and preparations which give rise to highly exothermic reaction when in contact with other substances, particularly flammable substances;

(c) easily flammable: - substances and preparations which may become hot and finally catch fire in contact with air at ambient temperature without any application of energy, or

- solid substances and preparations which may readily catch fire after brief contact with a source of ignition and which continue to burn or to be consumed after removal of the source of ignition, or

- liquid substances and preparations having a flash point below 21º C, or

- gaseous substances and preparations which are flammable in air at normal pressure, or

- substances and preparations which, in contact with water or damp air, evolve highly flammable gases in dangerous quantities;

(d) flammable:

liquid substances and preparations having a flash point between 21º C and 55º C;

(e) toxic:

substances and preparations which, if they are inhaled or taken internally or if they penetrate the skin, may involve serious, acute or chronic health risks and even death;

(f) harmful（有害）:

substances and preparations which, if they are inhaled or taken internally or if they penetrate the skin, may involve limited health risks;
（化學品被吸入人體或滲入皮膚內，可能會造成有限的健康危害）

(g) corrosive:

substances and preparations which may, on contact with living tissues, destroy them;

(h) irritant:

non-corrosive substances and preparation

（參考：http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=CELEX:31967L0548:EN:HTML，中文字為本人加入）

閣下可以先參考這個定義，如果有疑問在下可以在補充資料。

2015-04-26 10:58:50 補充：
GHS 最新的符號沒有「有害」這個危險性符號，「Health hazard」與以前的「Harmful」類似。

2015-04-26 11:00:04 補充：
樓主指的歐盟危險性符號中最被廣泛使用的危險性符號請參看在下的回答，當中已列明「Harmful（有害）」的定義，讓在下在此處再重申：

(f) harmful（有害）:

substances and preparations which, if they are inhaled or taken internally or if they penetrate the skin, may involve limited health risks;
（化學品被吸入人體或滲入皮膚內，可能會造成有限的健康危害）

P.S. 這個危險性符號編碼為 Xn，丁烷、乙醛、石腦油等均會被貼上「有害」的符號。

See here:

http://en.wikipedia.org/wiki/European_hazard_symbols

Please note - these symbols are no longer in use and the UN system replaces the European system:

http://en.wikipedia.org/wiki/GHS_hazard_pictograms