Activities Involving Reactive or Unstable Substances
Hazards:
Chemicals that are unstable, those that undergo self-reaction and those which react violently with air, moisture or other materials can rapidly release large amounts of energy. Such energetic substances may possess the following hazards:
1. Combustion on exposure to air or in the presence of water;
2. Violent self-decomposition accompanied by deflagration (reaction proceeds at a rate slower than the speed of sound) or detonation (reaction proceeds faster than the speed of sound);
3. Fragmentation of vessel or containers;
4. Violent reactions or fires resulting from the contact or mixing of powerful oxidising agents with other substances.
5. Violent reactions or fires resulting from the contact or mixing of powerful reducing agents with other substances.
Risk Factors:
 Use of substances classified as “explosive” by the Chemicals (Hazard
Information and Packaging for Supply) Regulations 1994 (CHIP II) as amended 1996, or by the carriage of dangerous goods by Road and Rail
(Classification, Packaging and Labelling) Regulations 1994 as a
“Flammable Solid”, a “Combustible Substance”, a “Substance which in contact with water emits a flammable gas” or an Organic peroxide”;

Use of any chemical substance which is unstable at ambient temperature, which decomposes violently on heating, or in contact with air or water;

Storage of reactive or unstable substances for extended periods of time or at low temperatures if it results in crystallisation of the substance;

Extracting unstable solids from solution, allowing the evaporation of solvents or moisture from unstable substances or allowing such a solid to separate or dry out;

Use of unstable substances in plant or equipment with hot surfaces, with abrasive or moving parts that may initiate decomposition because of friction;

Use of thermally unstable substances (as reactants or products) in vessels or equipment which is not fitted with temperature and pressure controls, monitoring devices and fail to safety pressure and emergency relief venting;

Milling, grinding or sieving unstable substances;

Distilling, purifying or treating unstable substances in a way which removes any inhibitor or stabiliser;

Carrying out chemical reactions or processes with concentrated or undiluted reagents, using reagents of unknown or uncertain purity or under a potentially reactive atmosphere gas;
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
The uncontrolled rate of addition or mixing of unstable chemical reagents, the addition of excess or insufficient reagent to the reaction mixture or the use of viscous solvents which inhibit thorough mixing of the reagents;

The use of pyrophoric (Spontaneously combustible), peroxidisable, water reactive substances or those which react violently with fire extinguishing agents such as carbon dioxide or water containing foams;

The mixing of strong oxidising agents with flammable, readily combustible materials or other potential fuels or reductants.
Risk Control Measures:
1. Avoid working with reactive or unstable substances or mixtures of incompatible substances where practicable;
2. Use the smallest amount of reactive or unstable substance in an inert diluent;
3. Store reactive or unstable substances only in the way advised by the supplier and do not exceed any recommended storage period, stocks kept longer than any recommended period should be safely disposed of or tested (e.g. for the presence of peroxides) and purified where necessary before use;
4. Store reactive or unstable substances with materials that are likely to increase the hazard in the event of fire or spillage;
5. Do not allow apparatus, equipment or vessels containing reactive or unstable substances to dry out, be heated or re-used unless all residues have been removed;
6. Apparatus or vessels for use with reactive or unstable substances should be cleaned and dried before use and free of any contamination;
7. Apparatus or equipment used for the distillation or reaction of reactive or unstable substances should incorporate adequate temperature monitoring and control with suitable manual or automatic alarms to indicate the onset of hazardous condition, the apparatus or equipment should have sufficient strength to contain any foreseeable pressure increase, be fitted with a suitable pressure relief or venting device or positioned within a safe enclosure or barrier.
8. The order and rates of addition of reagents must be carefully controlled and the reaction mixture agitated or stirred to maintain uniform dilution;
9. Do not scale-up reactions or preparations involving reactive or unstable substances or change any reaction condition without a detailed risk assessment, reactions or preparations should not be left unattended;
10. Neutralise or treat reactive or unstable waste residue or surplus to render it safe for disposal or ensure that it is stored in closed containers in a safe place;
11. Reactive substances that are supplied with a stabiliser or inhibitor should not be stored or processed in such a way as to remove or reduce the concentration of the inhibitor;
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12. Protective screens or barricades of acrylic or polycarbonate resin should be used to enclose any hazardous reactions, personal protective equipment including full-face visor to BS2092:1CM, gloves to BSEN 374 and a laboratory overall must be worn.
Persons at Special Risk:
Undergraduates are unlikely to have knowledge and experience to handle safely reactive or unstable substances unless directly supervised.
Health Surveillance:
None necessary
Exclusions:
This model may not be suitable for work with substances classified as
EXPLOSIVE, SPONTAINEOUSLY COMBUSTIBLE, those self reactive substances classified as FLAMMABLE SOLIDS and those subject to the
Explosives Act 1875, the Manufacture and Storage of Explosives Regulations
2005 and associated Regulations.
Relevant Statutory Provisions and Other Guidance:
Management of Health and Safety at Work Regulations 1999
Dangerous Substances and Explosive Atmospheres Regulations 2002
Chemicals (Hazard Information Labelling) Regulations 1994, as amended 2002
Carriage of Dangerous Goods by Road and Rail (Classification, Packaging and
Labelling) Regulations 1994
Special Waste Regulations 1996
The Manufacture and Storage of Explosives Regulations 2005
Storage of packaged dangerous substances, HSE, HS(G)71
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