Interpretation and use of MSDS

For the better understanding and use of the Material Safety Data Sheet, some terms are explained below:

  1. Formula (Chemical):

It is a symbolic representation of chemical entity or relationship between elements, molecule and atoms. E.g. H2 one molecule of hydrogen, 2H2SO4 two molecules of sulphuric acid, H2O one molecule of water wherein there are two atoms of hydrogen and one atom of oxygen. C6H6 benzene contains six atoms of carbons and six atoms of hydrogen in one molecule, group or ion. Thus by formula we can know the hazardous ingredient of a chemical.

  1. Synonym:

Indicates alternate name of a material e.g. Di-methyl  ketone or 2-Propanone for Acetone.

  1. Trade Name:

Commercial name of the product.

  1. Chemical Classification:

General classification is organic or inorganic. Hazard wise classification can be flammable, explosive, toxic or poisonous, corrosive, reactive, infectious, oxidising, radioactive etc.

  1. CAS No:

It is Chemical Abstracts Service number to provide a single unique identifier with naming the chemical. E.g. CAS No. For acetic acid is 64-19-7. It does not indicate the hazards of a material.

  1. UN No:

It is United Nations four digit number assigned to potentially hazardous material (e.g Ammonia UN No. 1005) or Class of material (e.g. corrosive liquids UN No. 1760)

These numbers are internationally recognised and used by emergency response personnel (including fire fighters) to identify material during transport emergencies. UN, Hazchem, NA and PIN numbers have the same uses.

  1. Hazchem (EAC) No:

Hazchem (hazardous chemical) Code or EAC (Emergency Action Code) is an emergency code confirmed by the Health & Safety Executive UK. It consists of number (1 to 4) followed by one or two letters and signifies type of a fire extinguisher required, type of personal protective equipment required, whether the spillage should be contained or diluted with water, whether the material is received and whether evacuation of the surrounding area necessary. Hazchem No. Of Sodium cynide is 4X and that of Vinyl chloride is 2WE.

  1. ADR No:

It is an Agreement concerning carriage of Dangerous goods by Road. This European agreement was arrived at Geneva by 19 European countries for the safety of international transport by road. If deals with the classification of hazardous substances, their packaging, loading and unloading, transportation and its equipment. It gives hazard identification numbers like UN hazard class number. Their comparison is given below.

Classification of Dangerous Goods By
UN Number ADR Number
1 Explosive. 2 Emission of gas due to pressure or due to chemical reaction.
2 Gases-Compressed, liquefied, dissolved under pressure or deeply refrigerated. 3 Flammability of liquids (vapours) and gases.
3 Flammable liquids. 4 Flammability of gases.
4 Flammable solids. 5 Oxidising (fire intensifying) effect.
5 Oxidising substances or Organic Peroxides. 6 Toxicity.
6 Poisonous (Toxic) or Infectious substances. 8 Corrosively.
7 Radioactive substances. 9 Risk of spontaneous violent reaction
8 Corrosive substances.
9 Miscellaneous dangerous substances.


Doubling (repeating) of an ADR digit indicates increase of that particular hazard. Prefix ‘X’ indicates that the substance can dangerously react with water. As an example ADR HIN (Hazard Identification No.) of Benzene is 33 (UN No. Is 1114 and Hazchem No. Is 3WE)

  1. Appearance, State, Odour:

Appearance includes colour. State means physical state-solid, liquid or gas. Order indicates smell. Odour threshold is that minimum level (ppm) where the odour will start. If odour threshold is lower than the permissible safe limit (e.g. TLV, STEL. IDLH or LC), the odour indicates the presence of gas and some safety margin is available to run away or to take precautionary step. But if it is higher, the gas becomes toxic or hazardous before its odour starts and this condition is risky. In that event a reliable gas detector is useful. Sometimes odour is added to detect the gas leakage e.g. addition of mercaptan in domestic LPG. Ability to detect odour may vary from person to person and may mislead if the other odorous materials are simultaneously present.

  1. Specific Gravity (water=1):

It is the ratio of the density of a material to the density of water (which is 1 g/cc). Lighter material ( <1, e.g. benzene0.88) will float and heavier material (Sp. Gr>1 e.g. sulphuric acid 1.84) will sink. This information is useful for spill or fire control.

  1. Vapour Density (air=1):

It is the vapour weight per unit volume. In MSDS it is given as the ratio of the density of a gas or vapour to the density of air. The air density is 1.293 gm/1, but here it is considered as 1 for easy comparison of gases. Lighter gases (Vd<1, e.g. ammonia 0.59) will go up (rise) in the air and heavier gases (Vd>1, e.g. chlorine 2.49) will come down on the bottom. This information is useful for ventilation design and evacuation (emergency) activity.

  1. Boiling Point:

It is that temperature at which the material changes from a liquid to gas. Below this point the liquid can evaporate to from vapour but at the Boiling Point the change from liquid to vapour is faster. This increases the vapour concentration and its pressure. This condition poses higher risk of fire, explosion or toxicity.

  1. Thermal Decomposition Products:

If the material decomposes (break down) without boiling, the temperature at which it decomposes is given with the word ‘dec’ some of the decomposition products are hazardous. The thermal decomposition products may be quite different from the chemicals formed by burning the same material (hazardous combustion products). Information regarding thermal decomposition is useful to design ventilation system where a material may be heated.

  1. Hazardous Decomposition Products:

They are formed when a material decompose (without heating) because it is unstable or reacts with common material like water or oxygen. This information is useful to design storage and handling procedures. For example, phosgene decomposes into corrosive and toxic fumes of HCL and CO because of heating or coming into contact of water or steam. Here HCL and CO are hazardous decomposition products.

  1. Hazardous Combustion Products:

These are the chemicals which are formed when a material burns They may be toxic, flammable, smoke, carbon particles or other hazards. Their amount varies according to temperature and oxygen available. They may be different from the thermal decomposition products. This information is useful to decide the fire fighting material and procedure.

  1. Melting Point:

It is that temperature at which a solid material melts and becomes a liquid. This information is useful for storage and handling purpose.

A melted material may distort a container.

  1. Freezing Point:

It is that temperature at which a liquid material freezes and becomes solid. This information is useful for storage and handling purpose.

A frozen material may burst a container.

  1. Vapour Pressure:

It is the pressure (mm of Hg) upon atmosphere of the vapour of a material at a fixed temperature (e.g. 20 degree centigrade). Higher vapour pressure indicate higher concentration and therefore higher hazard due to fire or inhalation.

  1. Solubility:

It is the ability of a material to dissolve in water or another liquid (solvent). It may be expressed as a ratio or described by words like insoluble, very soluble, sparingly soluble or miscible. This information is useful to decide a scrubbing media, spill control or fire fighting material and procedure. Such solvent should not be hazardous.

  1. Scrubbing neutralising or inactivating media:

These are those materials (liquids) which dissolve or react with the hazardous material (gas, liquid or solid) to diminish its hazardous exposure e.g. caustic, lime, water etc. If this is not possible, proper absorbent may be used e.g. sand, sponge rubber etc.

  1. pH:

It is a measure of the acidity or alkalinity (basicity) of a material when dissolved in water. It is expressed in a scale from 0 to 14 as under:

pH                     0 – 2   Strong Acid

3 – 5     Weak acidic

6 – 8    Neutral

9 – 11   Weak basic

12 –14 Strong basic

  1. Flash point:

It is the lowest temperature at which a material gives off enough vapour near its surface to from a flammable air vapour (gas) mixture so that it can be ignited if a spark is available. The lower flash point indicates higher hazard as it can cause fire at a lower temperature. It is expressed as Closed Cup (CC) or Open Cup (OC). CC value is slightly less than the OC value.

  1. Auto-ignition Temperature:

It is the lowest temperature at which a material begins to burn in air without any contact of spark or flame. During heating if the material decomposes, the decomposed chemical may auto-ignite at some other temperature. Different test methods give different auto-ignition temperatures for the same material. Therefore this value is an estimate. The material should be stored, processed or handled well below its auto-ignition temperature to avoid the risk of self fire or explosion.

Substances liable to spontaneous combustion are those liable to spontaneous heating under normal conditions or to heating up contact with air and being then liable to catch fire.

  1. Flammable or Explosive Limits (LEL/UEL):

The lowest concentration (percentage in air) of gas or vapour which will burn or explode if ignited is called the Lower Explosive (or Flammable) Limit i.e. LEL or LFL. The upper concentration (percentage in air) of gas or vapour which will burn or explode if ignited, is called Upper Explosive (or Flammable) Limit i.e UEL or UFL. The range between LEL  and UEL is called the Explosive (or Flammable) Range. The fire or explosion risk lies within this range but not out of it. Below LEL the gas-air mixture is too lean to ignite and above UEL it is too rich to ignite.

However the concentration above UEL should be considered dangerous as due to entrainment of fresh air, it may be diluted and enter the explosive range. Similarly after LEL if gas discharge s continued in the same air it can also enter the explosive range. Thus explosive range can be reached depending on flow of gas and air affecting their concentration. Air and gas temperature may also affect. Therefore the range should be considered as approximate values. For gas/vapour it is expressed in % of air (1%=10000 ppm) and for power in gm/m3 of air.

This information is useful to avoid the conditions leading to the explosive range and to ascertain it before allowing any person to enter any vessel or confined space where such air-gas mixture is suspected. Explosion-meters are available to detect this range. Detection should be of percentage of LEL and all safety devices (alarms, controls, trips etc.) should operate well below the LEL Fire hazard should be prevented at pre-determined percentage of LEL.

  1. TDG Flammability:

Transport of Dangerous Goods (TDG) classifies the materials according to their flammability as under-

  • 2.1 Flammable gas.
  • 3 Flammable liquid (Sub classes 3.1, 3.2, and 3.3 based on flash point).
  • 4.1 Flammable solid.
  • 4.2 Spontaneously combustible material.
  • 4.3 Material which gives off a flammable gas on contact with water.
  1. Explosion Data (Sensitivity):

It gives explosive properties of a material e.g. low, moderate or high. It gives two types of sensitivity:

Explosion Sensitivity to Impact – It indicates whether or not the material will burn or explode on shock or friction.

Explosion Sensitivity to Static Electricity – It indicates how readily the material can be ignited by an electric spark or static discharge.

  1. Explosive Material:

An explosive material is that material which can explode on impact or by electric spark. Schedule-1 of Manufacture, Storage and Import of Hazardous Chemicals Rules, 1989 defines ‘Explosive’ as those chemicals which explode under the effect of flame, heat or photo-chemical conditions or which are more sensitive to shocks or friction than dinitrobenzene (old definition) or pyrotechnic substance (firework) or which is capable of producing gas at such temperature, pressure and speed to cause damage to surrounding or exothermic reaction by heat, light, sound, gas, smoke or their combination.

  1. Combustible and Flammable Material:

Flammable solid, liquid or gas which can catch fire and burn rapidly or explosively are flammable materials.

The terms combustible and flammable both indicates the ability of a material to burn. Any material that will burn at any temperature is combustible by definition. Flammable are a special group of combustible materials that ignite easily and burn rapidly. For example, NaCl, CCl4 and CO2 are non-combustible while sugar, cellulose and ammonia are combustible but non-flammable.

The more readily ignition occurs, the more flammable the material, less easily ignited materials are said to be combustible, but the line of demarcation is difficult to decide.

  1. Corrosive Material:

It can attack (corrode) metals or human tissues such as skin or eyes. Structure or metal container may become weak and eventually collapse or leak. Skin, eyes or other body parts can be badly affected (burning) by corrosive materials. Acids, halogen gases, chlorides, caustic, phenol etc. are corrosive.

  1. Hazardous Polymerisation:

Polymerisation is the process of forming a polymer by combining monomers into long chains. Uncontrolled polymerisation can be hazardous, as it can cause heat, pressure or explosion. Some chemicals can polymerise on their own without warning, other upon contact with water, air or common chemicals. Vinyl chloride rapidly polymerises in presence of light air or heat. Therefore polymerising conditions should be controlled properly. Inhibitors (negative catalysts or compounds that retard or stop an undesired chemical reaction such as polymerisation, oxidation, corrosion etc.) are normally added to products to reduce or eliminate the possibility of hazardous polymerisation.

  1. Pyrophoric Material:

Any liquid or solid that will ignite spontaneously in air at about 54.4 degree centigrade. Titanium dichloride and phosphorous are examples of pyrophoric solids, tri-butyl-aluminium and related compounds are pyrophoric liquids. Sodium, butyl-lithium and lithium hydride are spontaneously flammable in moist air as they react exothermically with water. Such materials must be stored in inert gas or under kerosene. Some alloys (barium, misch metal) are called pyrophoric because they spark when slight friction is applied.

  1. Oxidiser and Peroxide:

It is a compound that spontaneously evolves oxygen either at room temperature or under slight heating. Oxidisers include peroxide, chlorates, per-chlorates, nitrates and permanganates. These can react vigorously at ambient temperatures when stored near or in contact with reducing materials (that will remove oxygen or add hydrogen) such as cellulose and other organic compounds. Storage area should be well ventilated and kept as cool as possible.

  1. Chemical Stability:

A stable compound does not easily decompose or react readily. Chemical stability is the ability of material to remain unchanged in the presence of heat, moisture or air. An unstable compound may decompose, polymerise, burn or explode under normal environmental conditions. Special precautions are required to store or handle unsafe materials.

  1. Incompatibility:

Incompatibility means disability to co-exist permanently. Therefore incompatible materials should not be stored or kept together. For example, toluene react violently with some acids, plastic or rubber, therefore, these substances should be kept away.

  1. Reactivity:

Two or more chemicals can react with each other and give reaction products. E.g. 2H2+O2=2H2O. A single chemical can react with air or water (which are also chemicals) and give the product e.g. phosphorous burns in air and gives its oxides (P2O3, P2O5) sulphur burns and gives SO2 etc.

Reactions are exothermic when they evolve heat and are endothermic when they need heat to maintain them. A reversible reaction is one in which the reaction product is unstable and goes back to the original substance spontaneously.

  1. Hazardous Reaction Products:

These must be known for the safety of process, workers and environment. Here products are more important than the reaction because of their hazardous nature e.g. Chlorine reacts with alcohol and forms explosive alkyl hypochlorite. If toxic fumes are to be generated scrubbers are required, if flammable vapours are generated, inert gas blanketing is required and earthing of the vessel also becomes necessary. If reaction products are higher poisonous like NaCN, HCN etc, they are to handled in a closed system.

  1. Health Hazard Data:


TLV and STEL are given in 2nd Schedule of the Factories Act. LD50 and LC50 are given in 1st Schedule of the MSIHC Rules for the purpose of major accident hazard LD50 for insecticides are given in Rule 19 of the Insecticide Rules for labelling purpose. Lower these values, higher the toxicity. LD50 up to 200mg/kg and LC50 up to 10 mg/1 can cause major hazard. By local exhaust ventilation toxic gas, dust or vapour must be captured and effective PPE must be worn by the workers. Above STEL, SBA is desirable.

  1. Tremcard:

Transport Emergency Cards are to be given to the drivers carrying dangerous goods for emergency information which may be needed at any time during journey. The cards contain short information on nature of chemical hazards involved, protective device, emergency action for fire, spillage, leakage, first-aid etc.

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.