UN Manual of Tests
Explosion Testing for dust, gases & vapours
© January 2026

UN 4.1 Classification test for flammability of solids (test N.1)

The UN flammability of solids test (N.1) is similar to the train firing test, but includes a wetted zone in the substance train to determine which packing group is applicable in Division 4.1 (readily combustible solids). Testing is required for dangerous materials under the UN Recommendations on the Transport of Dangerous Goods.

UN 4.2 Classification test for substances liable to spontaneous

combustion (self-heating test N.4)

The UN 4.2 classification test (self-heating test N.4) is similar to the isothermal basket test, but groups materials based on ignition / non ignition in two sizes of basket and at three different oven temperatures. Testing is required for dangerous materials under the UN Recommendations on the Transport of Dangerous Goods.

UN 4.3 Classification test for substances which in contact with water

emit flammable gases (test N.5)

A series of screening tests on small and medium quantities of sample are undertaken initially to see if gas is emitted when in contact with water and whether spontaneous ignition of the gas occurs. In a subsequent test, water is gradually added to a larger test sample and emitted gas is collected over a period of time (up to a maximum of 5 days). If the chemical identity of the gas is unknown, its flammability is tested. Testing is required for dangerous materials under the UN Recommendations on the Transport of Dangerous Goods.

UN test for pyrophoric substances (test N.2)

In this test, small quantities of solids sample are poured from height onto a non-combustible surface and are observed whether the substance ignites during dropping or within 5 minutes of settling. Liquid samples are added to an inert carrier and exposed to air while being observed for ignition. A subsequent test involves applying the substance to filter paper and observing it for evidence of ignition or charring. In either case, a positive test results in the substance being classified as packing group I of Division 4.2. Testing is required for dangerous materials under the UN Recommendations on the Transport of Dangerous Goods.

UN Classification tests

Explosion Testing
© January 2026

UN 4.1 Classification test for

flammability of solids (test

N.1)

The UN flammability of solids test (N.1) is similar to the train firing test, but includes a wetted zone in the substance train to determine which packing group is applicable in Division 4.1 (readily combustible solids). Testing is required for dangerous materials under the UN Recommendations on the Transport of Dangerous Goods.

UN 4.2 Classification test for

substances liable to

spontaneous combustion

(self-heating test N.4)

The UN 4.2 classification test (self-heating test N.4) is similar to the isothermal basket test, but groups materials based on ignition / non ignition in two sizes of basket and at three different oven temperatures. Testing is required for dangerous materials under the UN Recommendations on the Transport of Dangerous Goods.

UN 4.3 Classification test for

substances which in contact

with water emit flammable

gases (test N.5)

A series of screening tests on small and medium quantities of sample are undertaken initially to see if gas is emitted when in contact with water and whether spontaneous ignition of the gas occurs. In a subsequent test, water is gradually added to a larger test sample and emitted gas is collected over a period of time (up to a maximum of 5 days). If the chemical identity of the gas is unknown, its flammability is tested. Testing is required for dangerous materials under the UN Recommendations on the Transport of Dangerous Goods.

UN test for pyrophoric

substances (test N.2)

In this test, small quantities of solids sample are poured from height onto a non-combustible surface and are observed whether the substance ignites during dropping or within 5 minutes of settling. Liquid samples are added to an inert carrier and exposed to air while being observed for ignition. A subsequent test involves applying the substance to filter paper and observing it for evidence of ignition or charring. In either case, a positive test results in the substance being classified as packing group I of Division 4.2. Testing is required for dangerous materials under the UN Recommendations on the Transport of Dangerous Goods.