Technical-Scientific Safety Report:

Safety of Hydrogen, LPG, and CNG Tanks in Urban Central Storage Operations

Risk Analysis, Protection Concepts, and Scenarios of Multiple Chain Reactions in Metropolitan Centers

1. Introduction

The urbanization of global civilization and the transition to alternative energy sources bring with it novel safety challenges. Hydrogen (H₂), liquefied petroleum gas (LPG), and compressed natural gas (CNG) are considered the key energy sources of the future. Their storage, especially in urban central warehouses within densely populated metropolitan areas, represents a complex, multidisciplinary risk. This article analyzes the security requirements, identifies potential hazard chains, and develops protection and monitoring concepts for critical infrastructures.

2. Properties of the Energy Sources in the Context of Hazard Analysis

2.1 Hydrogen (H₂)

• Ignition Temperature: ~560°C

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• Explosion Limit: 4–75 vol% in air

• Diffusion Rate: Very high

• Special Features: Invisible flame, high explosion pressure, material embrittlement due to hydrogen embrittlement

2.2 LPG (Propane-butane mixture)

• Ignition temperature: ~470°C

• Explosion limit: 1.8–9.5 vol%

• Special features: Heavier than air, accumulates near the ground, delayed detonation upon outgassing

2.3 CNG (methane-based)

• Ignition temperature: ~595°C

• Explosion limit: 5-15 vol.%

• Special features: Lighter than air, diffuses upwards, more stable combustion behavior than H₂, but high pressure load

3. Typology of urban central warehouses

Urban central warehouses are usually multi-central storage and transshipment points for energy sources and specialty gases. Typical features are:

• Proximity to buildings (less than 500m from residential structures)

• Multi-tank configurations with different pressure regimes (e.g., 700 bar for H₂, 200 bar for CNG, ~7 bar for LPG)

• Combined infrastructure with power distribution, charging infrastructure, water supply, and AI-supported sensors

4. Main hazards: Multi-cascade effects & Chain Reactions

4.1 Primary Ignition Scenario

A localized defect (e.g., material failure of a pressure cylinder, valve rupture, thermocouple failure) can lead to the localized release of a gas. Depending on the concentration and ambient air, explosion or deflagration hazards arise.
Example: H₂ valve failure → leak → air mixing → ignition → Initial pressure wave.

4.2 Secondary detonation due to thermal radiation

The thermal radiation from an H₂ explosion reaches up to 2,000°C in the core area, which pushes neighboring LPG tanks beyond their permissible wall temperature limit.
→ BLEVE scenario (Boiling Liquid Expanding Vapor Explosion): Evaporating liquid contents lead to a tank explosion → Pressure wave + fragment projectile impact.

4.3 Tertiary reactions due to structural separation

A disrupted anchor point or fundamental structural loss due to a previous pressure wave can lead to chain reactions:

• Toppling of neighboring containers

• Failure of sensors or cooling circuits

• Delayed detonation due to delayed valve failure

5. Other conceivable escalation scenarios

5.1 Scenario: Blackout + Valve Failure + Heat Wave

• Heat >40°C for several days

• Power failure of the active cooling systems

• Thermal overpressure in H₂ systems
  →Multiple tank explosion (cascade) due to simultaneous overpressure relief

5.2 Scenario: Terrorist intervention via drone attack

• GPS-controlled micro-drone with burning thermite charge

• Target: Manual pressure valve of an LPG tank

• Result: Localized BLEVE, followed by chain explosion caused by shock pulse

5.3 Scenario: Cyberattack on Sensors

• Target: Temperature and pressure sensors provide incorrect data

• Automatic valve management opens several high-pressure valves simultaneously

• Creation of an explosive gas mixture in the controlled area → Initial explosion

6. Risk assessment & Safety Architecture

6.1 Quantitative Risk Matrix (QRA)

6.2 Protective measures

• Double passive shielding (sand-ceramic cladding, e.g., for H₂)

• Geodata-controlled anti-drone field generators

• AI-supported leak prediction through pattern recognition

• Locally separated tank areas with pressure wave deflectors

• Decoupling of infrastructure (e.g., hydrogen separated from LPG)

7. Strategies for Urban Integration

7.1 Subterranean Storage with Emergency Degassing

• Deep Bunker-Type Container Structure

• Overpressure-Proof Degassing Shafts with Activated Carbon Filtration

• Ideal for CNG and Hydrogen

7.2 Vertical Storage Architecture

• High-Rise Configuration with Zone Separation

• Advantage: Reduced floor space, better separation of Tank Types

• Disadvantage: Vertical chain reactions in the event of a structural collapse

7.3 Mobile Central Warehouses on Rail Systems

• Mini-central warehouses on the move that only remain temporarily in the city

• Possibility for rapid evacuation in the event of a crisis

8. Political, Legal, and Social Aspects

• Insurance Law: High coverage amounts required, hardly affordable for private operators

• Disaster Protection Legislation: Must be expanded to include gas-specific major damage scenarios

• Transparency Obligations: Citizen-oriented information obligations to reduce irrational fear reactions

• Civil Defense Exercises: Simulation of BLEVE and cascade scenarios in large cities

9. Conclusion and Outlook

Central storage facilities for hydrogen, LPG, and CNG in urban centers require the highest levels of safety precision, organizational redundancy, and resilient infrastructure. The real danger lies less in the explosion of a single container than in a multi-cascading escalation caused by the simultaneous failure of multiple safety systems.
The future lies in modular, AI-monitored, decentralized energy storage systems with automated crisis response. Only through interdisciplinarity—technology, psychology, sociology, and law—can this be achieved. A comprehensive safety concept can be guaranteed.

Appendix A: Example calculation formula for BLEVE pressure wave

Formula for shock wave energy of a BLEVE:
E = P V γ 1 γ (1 γ (P 0 P) (γ 1 ) / γ ) E = frac{P ≡ V} {γ - 1} ≡ left (1 - left (frac{P 0 P } right)^{(γ - 1) / γ } right)
With:

• EE: released Energy

• PP: Initial pressure in the tank

• VV: Volume

• P0P_0: Ambient pressure

• γgamma: Adiabatic exponent (e.g. 1.4 for methane)

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