Risk Codes
Chemical data sheets available in many countries now contain codes for certain "risk phrases", shown as R23, R45 etc. These risk phrase codes have the following meanings:

 R1

 Explosive when dry.

 R2

 Risk of explosion by shock, friction, fire or other source of ignition.

 R3

 Extreme risk of explosion by shock, friction, fire or other sources of ignition.

 R4

 Forms very sensitive explosive metallic compounds.

 R5

 Heating may cause an explosion.

 R6

 Explosive with or without contact with air.

 R7

 May cause fire.

 R8

 Contact with combustible material may cause fire.

 R9

 Explosive when mixed with combustible material.

 R10

 Flammable.

 R11

 Highly flammable.

 R12

 Extremely flammable.

 R13

 Extremely flammable liquefied gas

 R14

 Reacts violently with water.

 R15

 Contact with water liberates extremely flammable gases.

 R16

 Explosive when mixed with oxidizing substances.

 R17

 Spontaneously flammable in air.

 R18

 In use, may form inflammable/explosive vapour-air mixture.

 R19

 May form explosive peroxides.

 R20

 Harmful by inhalation.

 R21

 Harmful in contact with skin.

 R22

 Harmful if swallowed.

 R23

 Toxic by inhalation.

 R24

 Toxic in contact with skin.

 R25

 Toxic if swallowed.

 R26

 Very toxic by inhalation.

 R27

 Very toxic in contact with skin.

 R28

 Very toxic if swallowed.

 R29

 Contact with water liberates toxic gas.

 R30

 Can become highly flammable in use.

 R31

 Contact with acids liberates toxic gas.

 R32

 Contact with acid liberates very toxic gas.

 R33

 Danger of cumulative effects.

 R34

 Causes burns.

 R35

 Causes severe burns.

 R36

 Irritating to eyes.

 R37

 Irritating to respiratory system.

 R38

 Irritating to skin.

 R39

 Danger of very serious irreversible effects.

 R40

 Limited evidence of a carcinogenic effect.

 R41

 Risk of serious damage to the eyes.

 R42

 May cause sensitization by inhalation.

 R43

 May cause sensitization by skin contact.

 R44

 Risk of explosion if heated under confinement.

 R45

 May cause cancer.

 R46

 May cause heritable genetic damage.

 R47

 May cause birth defects

 R48

 Danger of serious damage to health by prolonged exposure.

 R49

 May cause cancer by inhalation.

 R50

 Very toxic to aquatic organisms.

 R51

 Toxic to aquatic organisms.

 R52

 Harmful to aquatic organisms.

 R53

 May cause long-term adverse effects in the aquatic environment.

 R54

 Toxic to flora.

 R55

 Toxic to fauna.

 R56

 Toxic to soil organisms.

 R57

 Toxic to bees.

 R58

 May cause long-term adverse effects in the environment.

 R59

 Dangerous to the ozone layer.

 R60

 May impair fertility.

 R61

 May cause harm to the unborn child.

 R62

 Risk of impaired fertility.

 R63

 Possible risk of harm to the unborn child.

 R64

 May cause harm to breastfed babies.

 R65

 Harmful: may cause lung damage if swallowed.

 R66

 Repeated exposure may cause skin dryness or cracking.

 R67

 Vapours may cause drowsiness and dizziness.

 R68

 Possible risk of irreversible effects.

 R20/21:

 Harmful by inhalation and in contact with skin.

 R20/21/22:

 Harmful by inhalation, in contact with skin and if swallowed.

 R20/22:

  Harmful by inhalation and if swallowed.

 R21/22:

  Harmful in contact with skin and if swallowed.

 R23/24/25:

 Toxic by inhalation, in contact with skin and if swallowed.

 R23/25:

  Toxic by inhalation and if swallowed.

 R26/27/28:

: Very toxic by inhalation, in contact with skin and if swallowed.

 R26/28:

  Very toxic by inhalation and if swallowed.

 R36/37:

  Irritating to eyes and respiratory system.

 R36/37/38:

 Irritating to eyes, respiratory system and skin.

 R36/38:

 Irritating to eyes and skin.

 R37/38:

 Irritating to respiratory system and skin.

 R42/43:

 May cause sensitization by inhalation and skin contact.

 R48/22:

 Harmful: danger of serious damage to health by prolonged exposure if swallowed.

 R50/53:

 Very toxic to aquatic organisms, may cause long-term adverse effects in the aquatic environment.

 R51/53:

 Toxic to aquatic organisms, may cause long-term adverse effects in the aquatic environment.

 R52/53:  

 Harmful to aquatic organisms, may cause long-term adverse effects in the aquatic environment.