Segregation techniques

Information on techniques used to separate dangerous goods, including the use of distance or inert materials, cut-off storage, and detached storage.

When segregating hazardous chemicals the following methods are generally used:

• segregate using distance or by using inert materials
• segregate using cut-off/partitioned storage areas
• segregate using detached storage
• ensure that incompatible goods are not stored above one another.

Using distance or inert materials

You can use distance or inert (mutually compatible) materials between incompatible goods when materials will not react violently together. A minimum separation distance of 3m will generally be suitable for most hazardous chemicals that are dangerous goods of packing group III.

You should take extra care with those hazardous chemicals that are equivalent to dangerous goods assigned to packing group II, as these can be more reactive or more dangerous in other ways (e.g. highly toxic). Where one or more of the incompatible goods are assigned to packing group II, or if they may react dangerously, a minimum segregation distance of 5m is recommended.

'React dangerously' means reactions that create a hazard because they:

• are violent
• produce an explosion
• produce a potentially explosive combination of products
• produce a fire or rapid evolution of heat
• produce toxic vapour or toxic gas.

Avoiding violent reactions

Where a violent reaction between hazardous chemicals may occur, it may be necessary to consider using cut-off storage where goods are stored in separate areas. The HAZCHEM code can be used as a tool to indicate whether there is an increased likelihood of a violent reaction. The possibility of a violent reaction should be considered if the second character in the HAZCHEM code for that chemical is a P, S, W or Y.

Curbing, ramps, bunding or depressed floor areas can be used to prevent the flow and interaction of incompatible liquids. Distances should be measured from the edge of the spills containment system.

Where both incompatible goods are solids and such solids are not likely to melt in the event of a fire, the minimum segregation distance can be reduced to 1 m.

Segregation using distance or inert materials may be suitable for dangerous goods such as class 3 dangerous goods and class 6.1 goods or ordinary combustible matter (not combustible liquids) and oxidising agents.

Cut-off storage

Cut-off storage is the use of separate rooms or compartments within a building to isolate incompatible goods. The rooms are separated by fire rated partitions that are impervious to vapours and liquids.

A fire resistance wall of at least FRL 120/120/120 fire rating for the partition is recommended.

Use of partitioned areas is useful for those materials that may react violently or offer high burning rate (e.g. large stores of class 4.2 or 5.2 dangerous goods).

Detached storage

Detached storage involves storing incompatible dangerous goods in separate buildings. This kind of segregation is used for materials that possess severe fire, reactivity or health risk.

'Dangerous when wet' goods such as aluminium phosphide and calcium carbide are materials that would warrant such precautions. Aluminium phosphide reacts with water to give off phosphine, a toxic and flammable gas. Calcium carbide reacts with water to generate acetylene gas.

A separate building that does not use water-based fire protection systems is needed to ensure water is not applied to these materials.