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Physical & Chemical properties

Auto flammability

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Description of key information

The different forms of iron placed on the market were characterized for their auto-flammability and flammability properties.
Carbonyl Iron Powder is classified category 1 for self-heating and category 1 for flammability under EU Globally Harmonised System.
Reduced Iron Catalyst is classified category 1 for self-heating under EU Globally Harmonised System.
Non-classification of DRI:
Wet DRI in an oxygenated atmosphere can satisfy all the conditions to become a fire hazards. However the standard conventional test conditions for self-heating and reaction with water do not mimic the conditions required.
DRI is not classified for self-heating and reaction with water.

Key value for chemical safety assessment

Additional information

Phys-chem endpoint Carbonyl iron powder Iron powder Pig iron DRI  HBI Elemental iron

  Reduced Iron Catalyst

Electrolytic iron 

Self-heating Category 1 Self-heating NC NC NC NC NC   Category 1 self-heating NC 
Pyrophoric solid NC NC NC NC NC NC  NC NC
Solid flammability Category 1 Flammability NC NC NC NC NC  NC NC
Emission of gas in contact with water NC NC NC NC NC NC  NC NC 

NC: Not Classified

Specific discussion for Direct Reduced Iron (DRI):

The study made by Neil Birks and Abdul G. F. Alabi (1986 - Reactions leading to the auto ignition of Direct Reduced Iron) presented in the section IUCLID V "4.23 Additional physico-chemical information" establishes the mechanism of the ignition of a Direct Reduced Iron pile which involves water (under the gaseous form), heat from oxidation reactions, oxygen and hydrogen.

The tests described in the recommendations on the transport of dangerous goods – Manual of Tests and Criteria do not integrate all the conditions required to observe auto-ignition of Direct Reduced Iron and the emission of hydrogen.

- The UN Test N.4. “Test method for self-heating substances” is performed in an oven with natural air circulation with two test cubic samples of 25 mm and 100 mm side.

- The UN Test N.5. “Test method for substances which in contact with water emit flammable gases” is performed at ambient temperature (20°C°) with a small amount of the test substance (approximately 2 mm diameter).

None of the tests simultaneously combines air circulation, high temperature and contact with gaseous water. Hence none of the tests should lead to the classification of Direct Reduced Iron as a self-heating substance and substance which in contact with water emits flammable gas.

Specific Discussion for Reduced Iron Catalysts

Pre-reduced iron containing catalysts are regarded as self-heating for the following technical reason:


Pre-reduced catalysts contain finely divided iron particles held within the catalyst matrix. This structure is necessary for the efficient performance of the catalyst product.

The pre-reduced catalyst is stabilised by partial re-oxidation which forms a protective coating around each catalyst particle. Without this passivation layer, direct exposure of the reduced iron catalyst to air would result in a vigorous oxidation leading to a highly exothermic heat of reaction which would have the potential to propagate further in the presence of more catalyst and/or flammable material.

Consequently it is not possible to conduct testing of reduced iron as a finely divided powder as it is contained within a stabilised catalyst matrix.

DATA WAIVING STATEMENT: Regulation (EC) No 1907/2006, Annex VII, Column 2 (Specific rules for adaptation) Section 7.12 - Self-ignition temperature states:


"The study does not need to be conducted if - the substance is explosive or ignites spontaneously with air at room temperature"