Recognition and Assessment of Deteriorated Explosives
Federation of EuropeanExplosives Manufacturers
BLASTING PRACTICE
TECHNICAL BULLETIN No. 3
Recognition and Assessment
of Deteriorated Explosives
CONTENTS
1. INTRODUCTION
2. SHELF LIFE
3. CONDITION OF PACKAGING
4. SIGNS OF DETERIORATION
5. GENERAL ADVICE
The TECHNICAL BULLETIN N°1 has been published by the FEEM Blasting Working Group
in January 2001
FEEM is affiliated to CEFIC (European Chemical Industry Council)
Route1, Avenue F Van Nieuwenhuyse 4 – B1160 Bruxelles
TECHNICAL BULLETIN N°1
Recognition and Assessment
of Deteriorated Explosives
1. Introduction
From time to time, situations occur when explosive products reach the end of their shelf life or begin to show signs of deterioration. When such situations occur it will be necessary to examine the products to determine whether they are either safe to use or transport to a safe site for destruction.
The examination of deteriorated explosive products is potentially a very hazardous operation and it is therefore very important that people handling explosives can recognise the signs of deterioration. This will help to either prevent any accidental detonation of explosives which have increased in sensitivity, or avert a misfire where explosives have become insensitive.
2. Shelf Life
All explosive products have a shelf life or “use by” date which is the time period where manufacturers state that their products can be used safely and will perform within their designed specifications. The shelf life for any product is highly dependent upon the conditions which it has been subjected to during transport and storage.
Normally each manufacturer will issue a product safety data sheet for each product stating the shelf life, which should always be referred to. The shelf life period normally assumes storage in good, clean, dry conditions in the original packaging with average temperatures and humidity.
The figures below are typical shelf lives for a range of products stored in good conditions:
ProductShelf Life
Nitroglycerine Based Gelatines12 months
Nitroglycerine Based Powders 6 months
Watergel Explosives12 months
Emulsion Explosives12 months
ANFO 6 months
Blackpowder 5 years
Cast Pentolite Boosters 5 years
Detonating Cord 5 years
Safety Fuse 2 years
Plastic Igniter Cord Slow 2 years
Plastic Igniter Cord Fast 12 months
Slotted Connectors 2 years
Plain Detonators 18 months
Instantaneous Electric Detonators 2 years
Electric Delay Detonators18 months
Seismic Electric Detonators 2 years
Capped Fuse Assemblies18 months
Fuse heads/electric fuses12 months
Detonating Relays12 months
Shock Tube Detonators18 months
It is very important that explosive products are always stored in their original packaging so that the manufacturing dates on the package can be easily seen and referred to. It is always good practice to rotate the stock in magazines ensuring that products of older manufacturing dates are used first before their shelf life has expired.
When a product has exceeded its shelf life it does not always necessarily mean that the product cannot be used and likewise there may be certain situations due to poor storage and handling where products deteriorate before the end of the shelf life period. It is these conditions and noticeable signs that are important when assessing the condition and suitability of the products to be used.
3.Condition of Packaging
The first step to examine the condition of any explosive products is to assess the state of the packaging. A note should be taken of the dates of manufacture and a visual inspection can be carried out without moving them to confirm that the cases are dry and do not exhibit any obvious signs of distress.
If the dates of manufacture on the cases reveal that the products are beyond the quoted shelf life, then advice from the manufacturer should be sought to determine the best course of action or disposal method.
If inspection reveals that the cases exhibit signs of wetness it may be a result of either external causes due to storage in damp conditions or deterioration of the product occurring from within the case. In either event extreme care is necessary when conducting further investigation.
If it is suspected that the cause of wetness to any cases is due to exudation from within the case (especially NG based explosives) then advice should be sought from the manufacturer before proceeding. If the handling of such material is unavoidable then great care should exercised at all times taking care to prepare a clean area where the material is to be stored, free from contamination by dirt and grit. It is recommended that some form of sheet be placed on the ground to prevent any further contamination.
If the cases are physically damaged by crushing or a similar action, then they must be carefully restacked or repacked to prevent further damage. If opening of the cases reveals physical damage to the cartridges or products then their condition must be further assessed for their suitability for use before progressing. If there is any doubt as to the suitability for use then the manufacturer should be consulted.
When cases are stacked in magazines or stores, care should always be taken to prevent them from being stacked too high. Not only will this cause damage to the cases but it can also accelerate the deterioration process of explosives products such as nitroglycerine based gelatines through excess force being applied, which promotes the exudation process. Advice can be sought from the manufacturers with respect to the recommended stacking heights for each product.
4.Signs of Deterioration
Each explosive product demonstrates different signs of deterioration and these must be looked at individually for each product rather than generally.
Nitroglycerine Based Explosives
Nitroglycerine based explosives tend to darken in colour with increased age. This effect is accentuated at the ends of the cartridges where moisture has been absorbed and it may be accompanied by the exudation of liquid. It must always be assumed that this liquid contains nitroglycerine. In certain cases, where cartridges have been exposed to wet conditions, salts leached out by water can recrystallise outside the cartridge.
Advice should be sought from the manufacturer if exuding explosives is suspected and great care should be exercised if handling such material is unavoidable. Suspect cartridges and packing materials contaminated with nitroglycerine should be placed in fibreboard cases lined with a plentiful supply of clean, dry sawdust or other absorbent material, which should also completely cover it.
Ammonium Nitrate Fuel Oil Explosives (ANFO)
The deterioration of ANFO takes the form of both hard caking or excessive softening and liquefaction. Slight caking where the lumps yield to light finger pressure is usually unimportant but hard caking or excessive moisture penetration of the explosives renders it unsuitable for blasting.
Watergel Explosives
The deterioration of watergel explosives usually manifests itself in a breakdown of the gel into separate liquid and solid components and it may also appear as hardening of the explosive cartridge. Cartridges may also be swollen or distorted and salts in the composition may crystallise on the outside. In extreme cases, deterioration may be accompanied by an exothermic reaction and eventually there is a potential for spontaneous combustion.
Emulsion Explosives
Emulsion explosives can demonstrate similar signs of deterioration to watergels as they also may break down into liquid and solid components. Generally they exhibit a gradual hardening from the centre outwards during the deterioration process. Alternatively, the hardening can be seen by a formation of a hard crust or eggshell type formation at the surface.
Blackpowder
Blackpowder is affected by excessive moisture leading to lumpiness and caking, or by severe handling, which may lead to excessive fines.
Detonators
Delay and short delay detonators deteriorate with time, but these effects may not necessarily be apparent from an external examination. Generally, the delay times will vary from the design times with age, although the detonators will function as an initiator. Such products should be tested for compliance with delay times as well as functioning before a decision is made opposite future use. It is advised that the manufacturers be contacted in such cases to carry out the appropriate testing.
Detonators showing signs of corrosion of the tubes are dangerous and must not be used. Particular care should be exercised when dealing with corroded detonators which become progressively more unstable when deterioration is obviously well advanced. This applies particularly to plain detonators that may have become wet and subsequently dried out, since the explosives charge may have become displaced and redeposited.
Copper tube detonators may exhibit green encrustation and should be treated with extreme care and handling should be avoided where possible.
If detonators with corrosion or any type of physical damage to the tubing are discovered they should not be used under any circumstances. Expert advice should be sought before determining the best course of action.
Capped Fuse
Capped fuse assemblies may deteriorate either through corrosion of the detonator shell or due to moisture penetration through the crimp area or through the fuse itself. If there is a doubt over the condition then the burning speed and operation should be checked before use.
Detonating Relays
Detonating relays may deteriorate beyond their shelf life producing erratic delay times. Corrosion of the aluminium inner tubes may also cause complete failure. Again if there is any doubt to their suitability their operation should be checked through test firing of a sample batch before use.
Detonating Cords
Almost the only cause of deterioration or desensitisation of detonating cords is moisture penetration of the explosives core load. It is unlikely that there will be any visible evidence of this and it is very difficult to detect. Occasionally powder gaps also occur in the core load and these are sometimes detectable by a thinning of the cord.
Another form of deterioration of detonating cord can be cracking in the outer casing, which is often constructed of plastic. This can be caused by either extremely cold weather conditions or through the general ageing of the product.
Safety Fuse
Deterioration of safety fuse is likely to be caused by dampness affecting the black powder core or kinks or abrasions to the outer carcass. Whatever the cause, it is likely that the burning speed will be affected and therefore the safety fuse should be tested before use and disposed of by burning if the burning speeds are found to be erratic.
Plastic Igniter Cord
The major sign of deterioration of all types of igniter cords is the drying out and cracking of the burning composition. Other causes of deterioration are abrasion or damage to the outer plastic carcass or the ingress of moisture through the core.
If there is any doubt in the condition of the igniter cord a burning speed test should be carried out before it is used.
5.General Advice
Only persons who are trained in the detailed examination and handling of time expired and deteriorated explosives products should undertake such work or give advice and recommendations how to handle such products.
Products which display obvious signs of deterioration or are beyond their quoted shelf life should never be used.
Users should always refer to the manufacturer’s safety and technical data sheets at all times, paying particular attention to the shelf life, physical properties and recommended storage conditions for each product.
If there is any doubt regarding the condition of any explosive’s products then the user should seek expert advice or consult the manufacturer for recommendations on how to proceed or handle the material.
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