Desensitised Explosives

Desensitised explosives are solid or liquid explosive substances which are wetted, diluted, dissolved or suspended in order to suppress or at least reduce their explosive properties.

However, desensitised explosives may become explosive again under certain circumstances - especially after long term storage and during handling and use, e.g. when the desensitising substance is removed or its concentration is decreased for example due to evaporation of water aka ‘drying out’ - and some desensitised explosives may retain explosive properties even in the desensitised state.

Therefore the storage of desensitised

explosives MUST be proactively managed

to ensure they remain desensitised.

Whenever desensitised explosives are no longer required for active research they should be safely disposed of immediately via the University Hazardous Waste disposal process. When completing the disposal form, no other chemicals should be listed on that particular form and the statement ‘A DESENSITISED EXPLOSIVE’ must be clearly written on the form together with any other relevant information on its age and/or condition etc.

Should there be genuine concern as to the status/stability of a desensitised explosive contact the safety office, do not attempt to open or transport the chemical unnecessarily as some ‘resensitised’ explosives may be friction or shock sensitive and could require removal by a specialist contractor.   

Legal Implications

The Explosives Regulations 2014 replaced previous explosives regulations and among other changes the new regulations have revised the registration and licencing requirements for the manufacture and storage of explosives.

Under the 2014 regulations, ‘explosive’ means:

(a) Any explosive article or explosive substance which would —

• If packaged for transport, be classified in accordance with the United Nations Recommendations as falling within Class 1; or be
• classified in accordance with the United Nations Recommendations as

  • being unduly sensitive or so reactive as to be subject to spontaneous reaction and accordingly too dangerous to transport, and falling within Class 1; or

(b) A desensitised explosive (i.e. a solid or liquid explosive that is wetted or dissolved to suppress its explosive properties, and which would be a Class 1 substance without that treatment).

As this is a very broad definition, it is not possible to provide an exhaustive list however some examples are shown in the table below.

Examples of Explosives Subject to Legislation

Note: This list is not exhaustive

Explosives

Those wishing to obtain and use explosives may need to apply for an explosives certificate / licence, see the HSE’s licence application page for more information.

There are exemptions to the need for certification and for storage licences. Schedule 2 to the regulations lists the substances that do not need a certificate to acquire or keep. The schedule is in two parts, the most relevant sections for research are probably in relation to 1- hydroxybenzotriazole (HOBt) in Part 1 and Sections 8 and 16 in part 2 which relate to:

8. Any desensitised explosive acquired, in a quantity not exceeding 5 grams, for the purposes of—

(a) research, analysis or testing at a University

16. A solution of the explosive substance 2,4, 6-Trinitrophenol (picric acid) in a concentration no greater than 2% weight per volume intended for use as an analytical reagent, stain, dye or fixative.

Potentially relevant exceptions to the need for a manufacturing licence can be found in Regulation 6 of the 2014 regulations ; in particular, whilst paragraph 1 states;

6.—(1) Subject to paragraph (2) (see below), no person may manufacture explosives unless that person holds a licence for that manufacture and complies with the conditions of that licence.

(2) Paragraph (1) (above) does not apply to—

(a) the manufacture of explosives for the purpose of laboratory analysis, testing, demonstration or experimentation (but not for practical use or supply) where the total quantity of explosives being manufactured at any time does not exceed 100 grams, but nothing in this sub-paragraph is to be taken as authorising any acquisition or keeping of explosives for which an explosives certificate is required by virtue of regulation 5, without such a certificate.

In addition exceptions for storage licences are in Regulation 7. Storage exemptions are typically short-term, and depend on the hazard type of the explosive. Hazard type is not an inherent property of a substance, as it depends on a number of factors such as the quantity of substance, how it is packaged, and how it is stored. Guidance on determining hazard type is available online from the HSE. One potentially important exemption for the University is that up to, but no more than, 5kg of hazard type 3 or 4 substances which are in Schedule 2 can be kept without a licence indefinitely.

If in doubt consult the local authorities.