Review of “old” incidents No.1
Noel Hsu
Expert Panel – Safex International
Introduction
SAFEX distributes incident notices—and, less frequently, full incident reports—to enable members to learn from real events across the energetic materials industry. Detailed reports from major incidents often require extensive internal approvals, which explains why they are less commonly released.
Several such reports exist within the SAFEX database. A standing section of the SAFEX Newsletter now revisits selected historical incidents, with members of the Expert Panel providing additional insights based on their experience. These views represent the experts’ interpretations and not those of the reporting company.
This review examines an explosion that occurred in 2008 at a dynamite manufacturing plant originally constructed in the 1960s. At the time of construction, the facility represented state-of-the-art technology. The plant operated for decades without a recorded incident until ownership changed in the early 2000s.
Summary
This report reviews the incident, describes the manufacturing process to provide context, outlines the investigation team’s findings, and highlights key learnings. Additional commentary explores historical accident patterns, the risks associated with long periods without incidents, and the value of retrospective hazard studies and risk assessments in legacy operations.
Description of the Dynamite Manufacturing Process
The facility consisted of a nitroglycerin (NG) manufacturing and storage plant, followed by dosing, mixing, tipping, cartridging, and packaging operations. Because NG is extremely hazardous to transport, dynamite plants typically produce NG on site.
A schematic of the process is shown in Figure 1.
Nitroglycerin Production
NG was produced by nitrating glycerin and glycol with nitric and sulfuric acids. After nitration, the mixture was neutralized and washed to remove residual acids and alkalis. Purified NG was then transferred to a dedicated storage building, physically separated from downstream operations.
Glycol was incorporated to moderate NG behavior—reducing sensitivity, lowering freezing tendency, and improving stability. This NG–glycol mixture is referred to simply as NG throughout this report
Gelatinization and Mixing
From storage, NG was transferred to the dosing annex of the Mixing Building and then into the mobile mixer bowl, where nitrocellulose (NC) was added. NC dissolves in NG, forming a gelatinized mixture that is significantly less sensitive to impact and friction than pure NG.
The NG–NC mixture was manually prepared and the bowl moved to another room where dry ingredients—such as TNT and ammonium nitrate—were added. The final unmixed composition was then transported to the Mixing Room and the bowl positioned below a remotely operated mixer shaft.
Figure 1. Schematic of the Dynamite Plant
Tipping and Cartridging
After mixing, the bowl was detached and moved to the Tipping Building, where the mixture was emptied into trolleys. These trolleys were then transported to the Cartridging Building for final product formation.
Operational Changes
By 2007, the plant operated two shifts and produced 9,400 tonnes of dynamite annually, with NG contents between 27% and 38%.
Two significant changes had been implemented after the acquisition:
- Installation of a new tipping unit for emptying mixed product into trolleys
- Installation of an NG detonation trap upstream of the mixing area
Description of the event
At approximately 14:40 during the second shift, an explosion occurred in the NG dosing area, including the NG transfer line up to the detonation trap. The explosion propagated to the tipping area, where several trolleys containing finished dynamite were staged for transfer. All were involved in the subsequent detonation.
The event is schematically shown in Figure 2. together with the masses involved in the explosions and the relative sensitivities of the products in the plant.
Figure 2. The Masses involved in the Explosion, and the Relative Sensitivities of the Products
A reconstruction indicated that:
• The tipping operator had just completed emptying a batch into two trolleys and was coupling them for transport.
• The mixing operator was either mixing NC and dye into NG or awaiting the addition of dry ingredients.
The alarm activated immediately, and personnel evacuated according to procedure. Emergency services arrived within minutes, and the area was secured by authorities.
Impact of the event
The incident resulted in:
- Two fatalities
- Eight injuries (one serious, seven minor)
- Extensive damage to buildings, equipment, and infrastructure in the dynamite area and adjacent operations
The detonation trap installed the previous year functioned as intended, preventing propagation to the 1,800 kg of NG in storage.
Likely causes
The investigation determined that two detonations occurred approximately 180 milliseconds apart, based on:
- Audio from a tourist’s video camera
- Reconstruction analysis
- Eyewitness accounts
The first detonation originated in the Mixing Building and propagated to the Tipping Building, likely through secondary effects such as shrapnel impacting exposed dynamite in the trolleys. Shock wave propagation was ruled out based on layout and timing analysis.
Three probable initiating scenarios were identified (in order of likelihood):
- Mechanical failure in the NG dosing/weighing area during valve closure
- Foreign body or excessive mechanical energy during manual mixing of NG, NC, and dye
- Failure during semi-automatic tipping of dry ingredients into the NG–NC mixture
Actions to prevent a recurrence
At the time of construction, detonation transmission of the type observed was not anticipated. Modern dynamite plants differ significantly, particularly in their use of remote operations.
Recommended actions included:
- Remote NG dosing and mixing
- Increased separation distances between mixing and cartridging operations
• Remote cartridging - Redesign to avoid simultaneous energetic operations and manual transfers
- After evaluating options, management elected to discontinue dynamite manufacture at the site.
Learnings
Key learnings:
Review Plant Design
Detonation transmission was not expected under the original Quantity Distance (QD) criteria. Legacy designs should be reassessed against modern understanding.
Personnel Location
Only essential personnel should be present during energetic operations. A non-essential worker had exited the building one minute before the explosion. He was unharmed.
Minimize Inventory
Maintain only the minimum necessary quantity of explosives in process.
Materials of Construction
Avoid glass windows in explosive buildings; glass fragments complicated cleanup and posed additional hazards.
Drills and Exercises
Regular emergency drills proved valuable and should continue.
Blast Consequences
Blast effects on adjacent structures—such as lightweight roofs, window frames, and interior walls—must be evaluated and mitigated.
Notably, a room containing 1,400 kg of unmixed gelatinized NG was protected by thick concrete walls and roof, preventing propagation.
Further Considerations
- 1. Historical Context
Biasutti’s compilation of explosives incidents (1652–1984) documents 188 dynamite accidents. Mixing/kneading and cartridging (Figure 3.) each account for 44% of events—consistent with the energy intensive nature of these operations and with the incident reviewed here. 
Figure 3. Distribution of Events showing Number and Percentage for the various operations
2. Long Periods of No Incidents
Extended periods of incident free operation can mask:
- Systemic drift
- Informal workarounds
- Outdated procedures
- Latent failures
This phenomenon—normalization of deviance, described by Dr. Diane Vaughan—can erode safety margins over time.
3. Precursor events (near-misses)
Near misses may go unreported or uninvestigated, allowing abnormal conditions to become normalized. Encouraging reporting and analysis of precursor events is essential.
4. Reduction of Consequences and Risk Management
Traditional standards such as the American Table of Distances (ATD) focus on consequence mitigation. Modern approaches incorporate quantitative risk assessment (QRA), enabling evaluation of both severity and likelihood. Tools such as IMESAFR support this approach.
5. Retrospective Hazard Studies and Risk Assessments
For acquired or legacy facilities, a retrospective HAZOP—supported by LOPA—provides critical insight into actual operating risk. Reviewing the management of change (MOC) system is equally important to ensure modifications remain within the basis of safety.
6. Conclusion
The cardinal rule of explosives safety—expose the minimum number of people to the minimum quantity of explosives for the minimum amount of time—was formalized within U.S. Department of Defense explosives safety doctrine and remains foundational across the industry.
The incident reviewed here reinforces the importance of:
- Minimizing explosive quantities
- Limiting personnel exposure
- Reducing consequences through design and separation
- Conducting rigorous hazard studies and risk assessments, especially for legacy or acquired assets
SAFEX acknowledges the member company that shared this report, enabling the broader industry to learn from this event.