Class 4.1: Flammable Solids & Solid Desensitized Explosives

Among all hazardous classes, 1 to 9, Class 4 has very diverse nature of divisions. In a series of articles let’s try to understand in layman’s term what these divisions represent as danger during transport by sea, what are the differences in emergency response out at sea for these divisions.

Class 4 is divided as below

Class 4.1     Flammable Solids

Class 4.1     Solid Desensitized Explosives

Class 4.1     Self-Reactive Substances

Class 4.2     Pyrophoric Solids

Class 4.2     Pyrophoric Liquids

Class 4.2     Self-Heating Substances

Class 4.3     Substances Which, In Contact With Water, Emit Flammable Gases

This article will cover description of Class 4.1 Flammable Solids & Solid Desensitized Explosives.

What are solids? Definition in the transport regulations says “Solids are dangerous goods, other than gases, that do not meet the definition of liquids in this regulation”. When we look at the definition of liquids we will know that paper or a book is solid. But will it make paper or book Flammable Solids? Answer to this question is, partially, YES! They are flammable but, paper and book, not flammable solids for transport regulations. So how do we decide which solids are flammable as per transport regulations?

Match heads - By Zapalky makro

For transport regulations, solids are flammable if they can be ignited by brief contact with an ignition source such as a burning match, and if the flame spreads rapidly (Readily combustible) or trough friction. This does not take into consideration of deliberately setting goods on fire, like in the case of arson.

United Nations Manual of Tests and Criteria, part III, 33.2.1, sets out the test procedure for flammable solids.

In the test if the burning time is less than 45 seconds and the flame passes through the wetted zone then the solids are considered as Class 4.1, packing group II. If the wetted zone zone stops the flame propagation for at least 4 minutes and if the burning time is less than 45 seconds packing group III is assigned.

Solids which may cause fire through friction are to be classified in class 4.1 by analogy with existing entries (such as matches) until definitive criteria are established and packing group for these solids shall be assigned by analogy with existing entries or in accordance with any appropriate special provision.

For metal powders or metal alloys if the zone of reaction spreads over the whole length of sample in 5 minutes or less packing group II is assigned. Packing group III should be assigned to metal powders if the reaction spreads over the whole length of the sample in more than five minutes but not more than ten minutes.

During test if the result of screening test and the burning rate test are negative then substance is not considered as readily combustible solids of class 4.1

Examples of Flammable Solids

  • HAY, STRAW or BHUSA
  • NAPHTHALENE
  • RUBBER SCRAP
  • MATCHES, SAFETY
  • FIRELIGHTERS, SOLID
Horses eating hay - Photo by BLW
Horses eating hay – Photo by BLW

Flammable solids and metal powders have different firefighting requirements. Most flammable solids are assigned with general fire schedule, which is to Create water spray from as many hoses as possible. For metal powders the recommendation is “If the fire is not igniting nearby cargoes, let the fire burn. Otherwise, cool the burning transport unit with copious quantities of water. Try to avoid getting water into the container.”

Explosives substances which are wetted with alcohols or water or diluted with other inert substances forming a homogeneous solid mixture suppressing their explosive properties are classified as solid desensitized explosives. The desensitizing agent is to be distributed uniformly throughout the substance. If this substance encounter lower temperature during transport which may freeze the water a suitable solvent like alcohol may be added to lower the freezing point. However the compatibility of the solvent with substance must be checked. Some of the solid desensitized explosives under class 4.1 is classified as Class 1 explosives when in dry state.

Class 4.1 Solid Desensitized Explosives

For solid desensitized explosives the firefighting on board ships is more dangerous due to the nature of cargo. When involved in fire the sudden short term events such as explosion may endanger the safety of the ship. All crew must be made aware that there is high explosion hazard with this cargo and must undertake firefighting from well protected area.

If the cargo is not on fire but spilled from ruptured packages the crew must avoid all sources of ignition which includes naked lights, unprotected light bulbs, electric handtools, friction and must wear non-sparking footwear. By using fire hose the spilled cargo must be wetted and never allowed to get dried. Wash away the spilled material over board with copious quantity of water.

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