Important lessons can be learnt from past accidents and incidents, including those which may be categorised as "near misses". An analysis of accident causes can indicate what problems might again arise in the future and the steps that should be taken to try to prevent any recurrence. As far as explosives events are concerned, the HSE analyzes the causes of such accidents on three levels. Firstly, the energetic stimulus which initiated the explosives material secondly, the immediate or proximate cause of the accident, i.e. the sequence of events which resulted in exposure of explosives to the stimulus; and thirdly, the underlying cause, i.e. any organizational deficiencies, oversights, etc. which allowed the sequence of events to occur in the first place. To take the previously cited example of a crane toppling onto explosives material, where this mishap was caused by human error, the causes might be stated thus:
| Stimulus: | Impact / friction |
|---|---|
| Proximate: | Fall of crane |
| Underlying: | Operative error |
However, underlying causes may be judged differently by various parties and it may often prove difficult to establish a unanimous opinion in the course of an accident investigation. For example, an incident which is ostensibly caused by operative error may have a deeper cause in such shortcomings as poor training, lack of supervision, failure of management to provide reasonable safeguards against human error, etc. Underlying causes thus normally need to be resolved in a court of law.
It is beyond the scope of this document to provide a comprehensive list of potential accident scenarios for each of the many types of processes and activities undertaken with explosives.
In the remainder of this appendix, a number of explosives accidents are discussed with respect to initiating stimuli and proximate cause. These examples illustrate the types of problems, which can arise and provide pointers to the type of information that should be included in a safety report with respect to both accident causes and safeguarding/mitigating measures.
The following two accidents were caused by objects falling onto explosives materials. No direct human action was involved in the first of these accidents; a badly fixed notice board simply fell off the wall onto some detonators that had been placed on a bench below. The second accident was caused by an operative inadvertently dropping a tool onto a sensitive explosives composition.
| Stimulus: | Impact / friction |
|---|---|
| Proximate cause: | Falling object |
| Date: | 16/02/44 |
| Location: | Explosives factory |
| Type of explosives: | Detonators |
| Type of activity: | Passive storage |
| Number of fatalities: | 0 |
| Two wooden carrying boxes containing detonators exploded in an unoccupied varnishing shop. It is believed that the plywood SSO board fell off the wall and hit the carrying box. | |
| Stimulus: | Impact / friction |
|---|---|
| Proximate cause: | Falling object |
| Date: | 07/05/86 |
| Location: | Explosives factory |
| Type of explosives: | Tantallium pressed powder |
| Type of activity: | Passive storage |
| Number of fatalities: | 0 |
| An Operative suffered burns to his hand after inadvertantly dropping a tool into a can containing phials of tantallium pressed powder. | |
Has the Operator considered the potential for objects to fall onto explosives?
Are there any engineered safeguards against such incidents (e.g. crash nets)?
Are there any procedural safeguards against such incidents (e.g. regular inspection and maintenance of danger buildings and fixtures and fittings therein)?
| Stimulus: | Impact / friction |
|---|---|
| Proximate cause: | Dropped explosives |
| Date: | 26/02/59 |
| Location: | Explosives factory |
| Type of explosives: | HMX |
| Type of activity: | Handling |
| Number of fatalities: | 2 |
| A charge of almost pure HMX exploded on being dropped. The accident occurred as the charge was being offloaded from a vehicle. The results of laboratory tests carried out on this type of explosive had suggested that it was not particularly sensitive to impact or friction. | |
This accident exemplifies the need for all explosives to be treated with caution. Although the results of the standard laboratory tests routinely carried out at the time prior to this accident had suggested that HMX was not particularly vulnerable to accidental initiation, further tests carried out after the accident showed that pressed charges of the explosives are sensitive to a combination of impact and friction. The moral of this story might be taken stated as "always expect the unexpected".
Pointers to look for in safety report
Has the Operator considered the possibility of explosives being dropped?
Are there any engineered safeguards against such incidents (e.g. crash mats)?
Are there any procedural safeguards against such incidents (e.g. training of staff in safe handling techniques)?
The following two accidents illustrate the potential danger from site transport. The first of these accidents exemplifies the need for explosives materials to be properly packaged for transport while the second simply exemplifies the need for explosives to be segregated from moving vehicles.
| Stimulus: | Impact / friction |
|---|---|
| Proximate cause: | Impact by vehicle |
| Date: | 06/06/51 |
| Location: | Explosives factory |
| Type of explosives: | Waste sludge contaminated with nitroglycerine (NG) |
| Type of activity: | Transport |
| Number of fatalities: | 2 |
| An explosion occurred on a bogie loaded with bagged waste sludge, which had been dredged from a settling pond used for collecting NG water washings from the nitration house. NG dripped from the waste onto the bogie wheels and detonated when the bogie was moved. The net explosives quantity (NEQ) was approximately 230kg. The explosion caused considerable damage to two explosives buildings 45 & 75 yds away and formed a crater 22 ft in diameter and 4 ft deep. | |
| Stimulus: | Impact / friction |
|---|---|
| Proximate cause: | Impact by vehicle |
| Date: | 04/03/80 |
| Location: | Explosives factory |
| Type of explosives: | Propellant |
| Type of activity: | Transport |
| Number of fatalities: | 2 |
| A truck carrying wet waste propellant toppled onto a tray causing an explosion that killed two workers. | |
Pointers to look for in safety report
Has the Operator considered the possibility of vehicles running into explosives?
Are there any engineered safeguards against such incidents (e.g. crash barriers)?
Are there any procedural safeguards against such incidents (e.g. vehicles inspection and maintenance, training of drivers)?
The following two accidents illustrate the need for high standards of housekeeping and maintenance of machinery within PES.
| Stimulus: | Impact / friction |
|---|---|
| Proximate cause: | Foreign object |
| Date: | 28/08/57 |
| Location: | Explosives factory |
| Type of explosives: | Nitroglycerine-based blasting explosives |
| Type of activity: | Cartridging |
| Number of fatalities: | 4 |
| An explosion occurred in a cartridging house whilst cartridges were being made on Miller-Dann semi-automatic extruders. The explosive contained 27% nitroglycerine. The explosion was initiated by frictional forces caused by the presence of a foreign body in the extruder. | |
| Stimulus: | Impact / friction |
|---|---|
| Proximate cause: | Foreign object |
| Date: | 05/06/91 |
| Location: | Explosives factory |
| Type of explosives: | Casting powder - propellant |
| Type of activity: | Mixing |
| Number of fatalities: | 0 |
| A detonation occurred during the process of incorporating casting powder. The accident happened during the final mixing phase shortly after ammonium perchlorate had been added to the mix. It was thought that the ignition may have been caused by the presence of a steel nut. | |
Pointers to look for in safety report
Has the Operator considered the possibility of foreign objects contacting explosives?
Are there any engineered safeguards against such incidents (e.g. guards over equipment)?
Are there any procedural safeguards against such incidents (e.g. regular inspection and maintenance of equipment)?
Friction-induced accidents caused by use of unauthorised tools or failure of Operatives to wear correct clothing
The details of the following accident illustrate the danger posed by the use of unauthorised tools.
| Stimulus: | Impact / friction |
|---|---|
| Proximate cause: | Assumed to be the use of unauthorised tool |
| Date: | 11/01/74 |
| Location: | Explosives factory |
| Type of explosives: | Pyrotechnic composition |
| Type of activity: | Cutting? |
| Number of fatalities: | 0 |
| An explosion occurred in a building where one man had just commenced manufacture of shop goods fireworks. The building, of brick with a light roof, was completely destroyed and the man later died of burn injuries. The cause of ignition could not be ascertained with certainty but a steel penknife belonging to the man was later found near the building, and it is considered that the accident may have been due to use of this unauthorised tool. | |
The details of the following accident illustrate the importance for Operatives to wear special clothing when working with sensitive types of explosives.
| Stimulus: | Impact / friction |
|---|---|
| Proximate cause: | Failure to wear correct clothing |
| Date: | 04/10/74 |
| Location: | Explosives factory |
| Type of explosives: | Propellant |
| Type of activity: | Drying |
| Number of fatalities: | 0 |
| An Operative entered the drying building without putting on overshoes. As he left, he heard a crack underfoot. This was followed by an explosion which hurled him down the escape tunnel. The building was destroyed. The Operative's shoe had a protruding nail. | |
There are many possible underlying procedural causes leading to such accidents, ranging from unforeseen danger to inadequate assessments of risk to poor training, poor supervision or straightforward Operator error.
Pointers to look for in safety report
Has the Operator considered the possibility of use of unauthorised tools or failure to wear correct clothing?
What procedural safeguards have been implemented (e.g. training of staff, supervision of staff, safety awareness and culture)?
Fire/heat-induced accidents - spread of fire from external source.
| Stimulus: | Fire/heat |
|---|---|
| Proximate cause: | Grass fire |
| Date: | 12/03/62 |
| Location: | Explosives factory |
| Type of explosives: | Black powder |
| Type of activity: | Storage |
| Number of fatalities: | 0 |
| Four buildings in a gunpowder plant were destroyed by fire and explosion. It is thought that glowing gorse embers from a railway embankment initiated the incident. The building nearest the embankment exploded and flying debris set fire to other buildings. | |
The following accident illustrates both the fire hazard posed by leaking equipment and how a fire starting externally to a building may spread and initiate explosives material.
| Stimulus: | Fire/heat |
|---|---|
| Proximate cause: | Leak of acid from pipeline |
| Date: | 09/12/67 |
| Location: | Explosives factory |
| Type of explosives: | NG-based blasting explosives |
| Type of activity: | Storage |
| Number of fatalities: | 0 |
| A leak of mixed nitric and sulphuric acid from a pipeline onto the grass below stated a fire which eventually consumed 4300 lbs of explosives. Initial first-aid fire fighting with a partially frozen 1" washing hose proved ineffective and may even have aggravated the fire. The fire spread to a hoist and thence along a wooden corridor to a mixing building containing 1000 lbs of blasting explosives. The fire brigade were by now controlling the fire when a partial detonation of the residue explosives fractured a water main. The fire was then spread by a strong wind to an adjacent mixing building containing approximately 3300 lbs of explosives. Fortunately, these explosives did not detonate but merely burned. | |
Pointers to look for in safety report
Has the Operator considered the possibility of fire spreading for external sources?
Are there any engineered safeguards against such incidents (e.g. low fire loading)?
Are there any procedural safeguards against such incidents (e.g. regular grass cutting, inspection of services, etc.)?
Fire/heat-induced accidents - hot surface
The following two accidents illustrate the danger posed by hot surfaces. The first accident occurred during a routine drying operation and brought to light some faults in the design of drying compartments which were subsequently corrected in a rebuilding programme. The second accident resulted from explosives material inadvertently coming into contact with a steam pipe.
| Stimulus: | Fire / heat |
|---|---|
| Proximate cause: | Assumed to be hot surface - poorly designed |
| Date: | 1967 |
| Location: | Fireworks factory |
| Type of explosives: | Igniter decomposition |
| Type of activity: | Drying |
| Number of fatalities: | 0 |
| An explosion occurred in the drying shed of a fireworks factory shortly before work was due to commence. The two buildings adjacent to the drying shed were wrecked by blast and flying debris. A person who was about to enter one of these buildings sustained both a fractured skull and shoulder. Though the precise cause of the accident could not be established, it was found that a small quantity of igniter composition had been kept for some time in an electrically heated air oven the design of which was such that it was possible for the material to be blown by the circulating fan onto the heater. | |
| Stimulus: | Fire / heat |
|---|---|
| Proximate cause: | Assumed to be hot surface - uncovered steam pipe |
| Date: | 11/12/67 |
| Location: | Explosives factory |
| Type of explosives: | Propellant |
| Type of activity: | Water steeping |
| Number of fatalities: | 0 |
| A fire and explosion occurred in a building used for the water steeping of propellant powders. The most likely cause of ignition was contact of propellant powder with a hot surface, possibly as a result of powder settling on steam pipes. The building was completely destroyed and there was considerable blast damage and some missile damage to other buildings within the factory. | |
Pointers to look for in safety report
Has the Operator considered the possibility of explosives contacting hot surfaces?
Are there any engineered safeguards against such incidents (e.g. lagging of pipes, guards in front of heaters, etc.)?
Are there any procedural safeguards against such incidents (e.g. high standards of housekeeping, etc.)?
The details of the following two accidents exemplifies the need for careful monitoring of process operations.
| Stimulus: | Fire / heat |
|---|---|
| Proximate cause: | Overheating |
| Date: | 05/12/85 |
| Location: | Explosives factory |
| Type of explosives: | Nitrocellulose |
| Type of activity: | Mixing / drying |
| Number of fatalities: | 0 |
| Nitrocellulose and dibutylphthalate were being mixed to make plastic core composition. The mixture was left unattended during the process of steam heating and mixing and this led to a runaway thermal decomposition. The vapour from the decomposing material caught fire ad this in turn triggered an explosion. | |
| Stimulus: | Fire / heat |
|---|---|
| Proximate cause: | Overheating of explosives and possible admixture with contaminants |
| Date: | 02/02/71 |
| Location: | Explosives factory |
| Type of explosives: | Pentolite |
| Type of activity: | Melting |
| Number of fatalities: | 0 |
| A fire followed by an explosion demolished a building used for melting and casting pentolite. A steam line had been left on during a break to melt a small quantity of pentolite. It is thought that a small amount of contaminant such as sulphur was also present. | |
As well as emphasising the need for careful monitoring of process operations, the details of this accident exemplify the importance of preventing explosives coming into contact with contaminants.
Pointers to look for in safety report
Has the Operator considered the possibility of explosives being heated to higher temperatures and for longer periods than intended?
Are there any engineered safeguards against such incidents (e.g. thermostats, high temperature cut-out devices, etc.)?
Are there any procedural safeguards against such incidents (e.g. regular monitoring of processes and equipment, etc.)?
There are numerous examples of explosives incidents caused by vandalism, sabotage and attempted robbery. Details of two such incidents are reproduced below:
| Stimulus: | Fire/heat |
|---|---|
| Proximate cause: | Vandalism |
| Date: | 14/09/70 |
| Location: | Fireworks factory |
| Type of explosives: | Black powder |
| Type of activity: | Storage |
| Number of fatalities: | 0 |
| A magazine containing 2000 lbs of gunpowder located outside the fence of a fireworks factory was destroyed in a series of explosions after work had ceased for the day. It was later established that some children had ignited some gunpowder on the step of the magazine, and this in turn set fire to waste cardboard cartons lying nearby. The magazine exploded as the children were running away. | |
| Stimulus: | Fire/heat |
|---|---|
| Proximate cause: | Attempted robbery |
| Date: | 05/10/95 |
| Location: | Storage area |
| Type of explosives: | Fireworks |
| Type of activity: | Storage |
| Number of fatalities: | 0 |
| A gang of burglars triggered a large explosion when they used welding equipment to break into a concrete bunker containing up to 700 fireworks, the total net explosives quantity being about 60 kg. The bunker was reduced to rubble. | |
Pointers to look for in safety report
Has the Operator considered the possibility of malicious action?
Buildings containing security-attractive items should be alarmed to an effective response force.
There are numerous examples of explosives accidents caused by static discharge. Details of one recent such accident is given below:
| Stimulus: | Static discharge |
|---|---|
| Proximate cause: | Use of electrically insulating material |
| Date: | 07/06/96 |
| Location: | Explosives factory |
| Type of explosives: | Pyrotechnic composition |
| Type of activity: | Storage hand sieving |
| Number of fatalities: | 0 |
| An Operative sustained temporary hearing loss as a result of an explosion of a small quantity of pyrotechnic composition he was hand sieving. Use of electrically insulating beakers and watch glasses in the process was the most probable cause of ignition. | |
Pointers to look for in safety report
Has the Operator considered the possibility of static discharge?
Are there any engineered safeguards against such incidents (e.g. earthing of machinery, anti-static floors, etc.)?
Are there any procedural safeguards against such incidents (e.g. regular checking of earthed equipment, use of anti-static clothing, etc.)?
There are also numerous examples of explosives accidents caused by lightning. The last such major accident recorded in the UK occurred in 1947 (brief details are given below). More recently (1987), lightning initiated a massive explosion at a dynamite plan in South Africa: eight tonnes of dynamite exploded producing a crater the size of a football field.
| Stimulus: | Static discharge |
|---|---|
| Proximate cause: | Use of electrically insulating material |
| Date: | 04/06/47 |
| Location: | Explosives factory |
| Type of explosives: | Nitroglycerine |
| Type of activity: | Washing |
| Number of fatalities: | 0 |
| An explosion occurred in an NG wash house containing 3300 lbs of nitroglycerine, which was divided between two pans. An additional 800 lbs of nitroglycerine was held in another pan but did not explode. The explosion was caused by lightning. The wash house was erected before the war and the lightning protection provided was of the type normally adopted for explosive buildings, i.e. the conductors were attached to the building. The separate pole system was later adopted, i.e. supporting poles were placed in the earth mounds surrounding the NG buildings, with the poles projecting 18 feet above the level of the mound or embankment. The investigating committee considered NG wash houses to be particularly vulnerable to electrical storms due to the unavoidable film of NG which is present on the lead surfaces in these wash houses. As NG will detonate when heated to a temperature of the order of 200ºC it does not require very much energy, either from direct flash or an induced charge at a metal surface to cause an explosion. | |
Pointers to look for in safety report
Has the Operator considered the possibility of lightning strikes?
Are there any engineered safeguards against such incidents (e.g. lightning protection system)?
Are there any procedural safeguards against such incidents (e.g. evacuation of buildings during electrical storms, etc.)?
Accidents cased by runaway chemical reaction during process operations
There have been numerous cases of explosives events at manufacturing sites caused by runaway chemical reaction during process operations. The proximate causes for such events include: addition of incorrect proportions of reactants to process equipment, addition of reactants in incorrect sequence, addition of contaminants to process equipment, inadequate mixing of reactants, failure to control process temperature and failure to stabilise material prone to spontaneous decomposition. For each of these broad proximate causes it is normally possible to identify a number of sub-causes, such as failure of process equipment (which in turn may be due to such factors as inadequate inspection and maintenance) and human error.
Brief details of two incidents caused by runaway chemical reaction are reproduced below: -
| Stimulus: | Runaway reaction |
|---|---|
| Proximate cause: | Incorrect proportion of reactants |
| Date: | 29/08/56 |
| Location: | Explosives factory |
| Type of explosives: | Dinitroresorcinol |
| Type of activity: | Nitrating |
| Number of fatalities: | 1 |
| There was an explosion in a dinitroresorcinol manufacturing plant. Due to insufficient nitric acid, a stick mass formed, partially blocking the discharge line. During the following nitration the material decomposed with fragments of a pipe killing a man. | |
| Stimulus: | Runaway reaction |
|---|---|
| Proximate cause: | Inadequate mixing |
| Date: | 03/03/92 |
| Location: | Explosives factory |
| Type of explosives: | Propellant |
| Type of activity: | Mixing |
| Number of fatalities: | 0 |
| A slow decomposition of NPP propellant occurred during the process of coating with TEGDM and AIBN. The decomposition was probably due to inefficient mixing, allowing hot spots to form as the exothermic polymerisation reaction progressed. | |
Pointers to look for in safety report
Has the Operator considered the possibility of runaway reaction?
Are there any engineered safeguards against such incidents (e.g. dumping and drenching systems)?
Are there any procedural safeguards against such incidents (e.g. training of staff, emergency procedures, etc.)?
Intermediate and finished explosives products may also be initiated by chemical reaction in the event that they are mixed with incompatible substances or become degraded. Some example incidents are given below:
| Stimulus: | Chemical reaction |
|---|---|
| Proximate cause: | Spontaneous combustion? |
| Date: | 29/05/58 |
| Location: | Explosives factory |
| Type of explosives: | Nitrocotton |
| Type of activity: | Storage |
| Number of fatalities: | 0 |
| An expense magazine containing 6500lbs of nitrocotton (most of it dry) exploded when nobody was in or near it. Extensive damage was caused to other buildings. The exact cause of the accident was not ascertained but was most probably due to spontaneous combustion. | |
| Stimulus: | Chemical reaction - reaction of copper with lead azide |
|---|---|
| Proximate cause: | Incompatible materials |
| Date: | 30/06/52 |
| Location: | Explosives factory |
| Type of explosives: | Ammunition |
| Type of activity: | Storage |
| Number of fatalities: | 0 |
| An explosion occurred during passive storage of derelict ammunition awaiting disposal on an open site. The 20 mm ammunition concerned was known to be in an extremely bad condition and many of the shell were heavily rusted. The exact case of the explosion was not found but the most likely explanation was that sensitive copper azide had been produced in one shell and that the high temperatures on the day of the incident caused movement of some part of the detonator which ignited the sensitive copper azide and fired the detonator. | |
| Stimulus: | Chemical reaction - corrosion |
|---|---|
| Proximate cause: | Incompatible materials |
| Date: | 05/02/70 |
| Location: | Quarry |
| Type of explosives: | Detonators |
| Type of activity: | Storage |
| Number of fatalities: | 0 |
| An explosion wrecked a magazine at a quarry. Corroded detonators were later recovered from the remains of the demolished building. | |
Pointers to look for in safety report
Has the Operator considered the possibility of contamination of explosives?
Are there any engineered safeguards against such incidents (e.g. testing of materials for compatibility)?
Are there any procedural safeguards against such incidents (e.g. high standards of house keeping, etc.)?
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