Chemical Classification and Grading

The core of chemical classification is based on hazard level. The global mainstream system uses GHS (Globally Harmonized System), while the United Nations TDG (Total Disturbance Classification) system is used for transportation.

GHS classifies chemicals into three categories : physical hazards, health hazards, and environmental hazards , with each category further subdivided into classes

The smaller the number, the more dangerous

Physical Hazards (Class 17, Core Classification)

Explosives : 1.1 (overall explosion) → 1.6 (extremely insensitive)

Flammable gases/aerosols : Category 1 (extremely flammable), Category 2

Flammable liquids : classified into 3 categories according to flash point/initial boiling point (Category 1 is the most dangerous).

Oxidizing gases/solids/liquids : Category 1 (strong oxidizers), Category 2

Self-reactive, spontaneously combustible, and ignition upon contact with water : all are classified according to their degree of hazard.

Metal corrosion products : Category 1 (strong corrosion)

Health Hazards (10 categories, core classification)

Acute toxicity (oral/dermal/inhalation): Category 1 (highly toxic) → Category 5 (slightly toxic) , classified by LD₅₀/LC₅₀.

Category 1: LD₅₀ ≤5 mg/kg (e.g., sodium cyanide)

Category 2: 5 < LD₅₀ ≤ 50 mg/kg

Category 3: 50 < LD₅₀ ≤ 300 mg/kg

Category 4: 300 < LD₅₀ ≤ 2000 mg/kg

Category 5: 2000 < LD₅₀ ≤ 5000 mg/kg

Skin corrosion/irritation : 1A/1B/1C (corrosion), 2 (irritation), 3 (mild irritation)

Severe eye injury/eye irritation : 1 (injury), 2A/2B (irritation)

Respiratory/skin sensitization , germ cell mutagenicity , carcinogenicity , reproductive toxicity , target organ toxicity , and inhalation hazards : all are classified as “Class 1 (high risk) → Class 2 (medium risk)”.

Environmental hazards (Category 2)

Harm to aquatic environments : Acute harm (Class 1/2/3), Chronic harm (Class 1/2/3/4)

Ozone layer depletion : Category 1 (damage)

The 9 categories of transport under the United Nations TDG (including packaging classification)

Used for sea/air/land transport, divided into 9 major categories , most of which are further subdivided into “items”, and categorized into 3 packaging categories according to the degree of danger :

Explosives (items 1.1–1.6)

Gases (2.1 Flammable, 2.2 Non-flammable and non-toxic, 2.3 Toxic)

Flammable liquids

Flammable solid / Spontaneously combustible / Ignites upon contact with water (4.1/4.2/4.3)

Oxidizing substances and organic peroxides (5.1/5.2)

Toxic and infectious substances (6.1 Toxic, 6.2 Infectious)

radioactive materials

Corrosive substances

Miscellaneous hazardous substances and articles (including environmental hazards)

Packaging level

Directly determines shipping costs and whether air freight is possible

Class I Packaging : Highly Dangerous → Strictest Requirements, High Shipping Costs, Many Air Freight Restrictions

Class II Packaging : Moderate Risk → Most Common

Class III Packaging : Mild Hazard → Relatively Relaxed

GHS ↔ UN Category ↔ Packaging Level Comparison (Most Commonly Used)

Chemical Hazard Codes

MSDS or chemical data sheets contain codes that indicate certain “hazard information,” such as R23, R45, etc. These hazard information codes have the following meanings:

R1: Explosive when dry;

R2: Hazardous of explosion when subjected to impact, friction, fire or other ignition sources;

R3: Extremely high risk of explosion when exposed to impact, friction, fire or other ignition sources;

R4: Generates extremely sensitive explosive metallic compounds;

R5: May explode when heated;

R6: Explosive with or without contact with air;

R7: May cause a fire;

R8: Contact with flammable materials may cause a fire;

R9: Explosion occurs when mixed with combustible materials;

R10: Flammable;

R11: Highly flammable;

R12: Extremely flammable;

R13: Extremely flammable liquefied gas.

R14: Reacts violently with water;

R15: Releases extremely flammable gas upon contact with water;

R16: Explosive when mixed with oxidizing substances;

R17: Spontaneously ignited in air;

R18: May generate a flammable and explosive vapor-air mixture when used.

R19: May generate explosive peroxides.

R20: Harmful if inhaled.

R21: Harmful upon skin contact.

R22: Harmful if swallowed.

R23: Toxic if inhaled.

R24: Toxic upon skin contact.

R25: Toxic if swallowed.

R26: Extremely toxic by inhalation.

R27: Extremely toxic upon skin contact.

R28: Extremely toxic if swallowed.

R29: Releases toxic gas upon contact with water.

R30: May transform into a highly flammable substance when used.

R31: Releases toxic gases upon contact with acids.

R32: Releases a highly toxic gas upon contact with acid.

R33: Risk of cumulative effect.

R34: Can cause burns.

R35: Can cause severe burns.

R36: Irritates the eyes.

R37: Stimulates the respiratory system;

R38: Skin irritant.

R39: There is a very serious risk of irreversible damage.

R40: May carry the risk of irreversible effects;

R41: Risk of serious eye damage.

R42: Inhalation may cause allergic reactions.

R43: Skin contact may cause an allergic reaction.

R44: Heating under sealed conditions poses a risk of explosion.

R45: Possibly carcinogenic.

R46: May cause irreversible genetic damage.

R47: May cause reproductive defects.

R48: Prolonged exposure poses a serious risk of health damage.

R49: Inhalation can cause cancer.

R50: Extremely toxic to aquatic organisms;

R51: Toxic to aquatic life.

R52: Harmful to aquatic life.

R53: Has long-term harmful effects on aquatic environments.

R54: Toxic to plants.

R55: Toxic to animals.

R56: Toxic to soil organisms.

R57: Poisonous to bees.

R58: May have long-term harmful effects on the environment.

R59: Harmful to the ozone layer.

R60: May reduce fertility.

R61: May cause harm to an unborn infant.

R62: Risk of impaired fertility.

R63: May be harmful to unborn infants.

R64: May pose a risk to breastfed infants;

R65: Swallowing this could damage the lungs.

R66: Repeated contact may cause dry or cracked skin.

R67: Steam may cause drowsiness and fainting.

R68: There is a risk of irreversible damage.

R20/21: Harmful if inhaled or in contact with skin.

R20/21/22: Harmful if inhaled, comes into contact with skin or is accidentally swallowed.

R20/22: Harmful if inhaled or accidentally swallowed.

R21/22: Harmful if ingested or through skin contact.

R23/24/25: Toxic by inhalation, skin contact and accidental ingestion.

R23/25: Toxic if inhaled or accidentally swallowed.

R26/27/28: Extremely toxic by inhalation, skin contact and ingestion;

R26/28: Extremely toxic if inhaled or accidentally swallowed.

R36/37: Irritating to the eyes and respiratory tract.

R36/37/38: Irritating to the eyes, respiratory tract and skin.

R14/15: Reacts violently with water, releasing extremely flammable gas;

R15/29: Releases toxic, highly flammable gas upon contact with water;

R23/24: Toxic by inhalation and skin contact;

R24/25: Toxic upon skin contact and ingestion;

R26/27: Extremely toxic by inhalation and skin contact;

R27/28: Extremely toxic upon skin contact and ingestion;

R36/38: Irritating to eyes and skin;

R37/38: Irritating to the respiratory system and skin;

R39/23: Toxic: Inhalation poses a serious risk of irreversible damage;

R39/23/24: Toxic: There is a serious risk of irreversible damage if inhaled or through skin contact;

R39/23/24/25: Toxic: There is a serious risk of irreversible damage if inhaled, through skin contact or ingested;

R39/23/25: Toxic: Inhalation and ingestion pose a serious risk of irreversible damage;

R39/24: Toxic: Skin contact poses a serious risk of irreversible damage;

R39/24/25: Toxic: Extremely serious and irreversible hazard upon skin contact or ingestion;

R39/25: Toxic: Ingestion poses a serious risk of irreversible damage;

R39/26: Extremely high toxicity: Inhalation poses a serious risk of irreversible damage;

R39/26/27: Extremely high toxicity: poses a serious risk of irreversible damage upon inhalation or skin contact;

R39/26/27/28: Extremely high toxicity: poses a serious risk of irreversible damage upon inhalation, skin contact, or ingestion;

R39/26/28: Extremely high toxicity: poses a serious risk of irreversible damage upon inhalation or ingestion;

R39/27: Extremely high toxicity: Skin contact poses a serious risk of irreversible damage;

R39/27/28: Extremely high toxicity: poses a serious risk of irreversible damage upon skin contact or ingestion;

R39/28: Extremely high toxicity: Ingestion poses a serious risk of irreversible damage;

R40/20: Harmful: May pose an irreversible risk if inhaled;

R40/20/21: Hazardous: There is a risk of irreversible damage if inhaled or through skin contact;

R40/20/21/22: Hazardous: There is a risk of irreversible damage if inhaled, through skin contact, or ingested;

R40/20/22: Hazardous: May pose an irreversible risk if inhaled or swallowed;

R40/21: Harmful: There is a risk of irreversible damage upon skin contact;

R40/21/22: Hazardous: There may be an irreversible risk of contact with skin and ingestion;

R40/22: Harmful: Ingestion may carry an irreversible risk;

R42/43: Inhalation and skin contact may cause allergic reactions;

R48/20: Hazardous: Prolonged exposure via inhalation poses a serious risk of health damage;

R48/20/21: Hazardous: poses a serious risk of harm to health through inhalation and prolonged skin contact;

R48/20/21/22: Hazardous: Prolonged exposure to the skin or through ingestion poses a serious risk of harm to health.

R48/20/22: Hazardous: Prolonged exposure via inhalation or ingestion poses a serious risk of harm to health;

R48/21: Hazardous: Prolonged skin contact poses a serious risk of harm to health;

R48/21/22: Hazardous: Prolonged contact with the skin or ingested poses a serious risk of harm to health;

R48/22: Hazardous: Ingestion or prolonged exposure poses a serious risk of harm to health;

R48/23: Toxic: Prolonged exposure via inhalation poses a serious risk of health damage;

R48/23/24: Toxic: There is a serious risk of serious health damage if inhaled or through prolonged skin contact;

R48/23/24/25: Toxic: Prolonged exposure to the skin or through ingestion poses a serious risk of serious health damage.

R48/23/25: Toxic: Prolonged exposure via inhalation or ingestion poses a serious risk of harm to health;

R48/24: Toxic: Prolonged skin contact poses a serious risk of harm to health;

R48/24/25: Toxic: Prolonged contact with the skin or ingestion poses a serious risk of harm to health;

R48/25: Toxic: Ingestion or prolonged exposure poses a serious risk of health damage;

R50/53: Extremely toxic to aquatic organisms and may cause long-term adverse effects in aquatic environments;

R51/53: Toxic to aquatic life and may cause long-term adverse effects in the aquatic environment;

R52/53: Harmful to aquatic life and may cause long-term adverse effects in the aquatic environment.