Finally, we have the comprehensive safety data we’ve been waiting for. EMSA’s H-SAFE study, published November 2025, delivers what the hydrogen shipping industry desperately needed: hard numbers showing exactly where our assumptions about adapting LNG systems fall short. As someone who’s reviewed countless “hydrogen-ready” designs that were really just LNG systems with blue paint, this report is a reality check. The message is clear—secondary enclosures around ALL leak sources aren’t a nice-to-have feature, they’re non-negotiable. And that includes piping on open deck.
The European Maritime Safety Agency (EMSA) just released the final report from DNV’s multi-year H-SAFE study investigating hydrogen fuel system safety. This isn’t another theoretical exercise—it’s quantitative risk analysis, HAZID workshops, and bowtie modeling across both compressed (CH₂) and liquefied (LH₂) systems. The findings fundamentally challenge the industry’s default assumption that hydrogen can be handled like LNG with minor modifications.
The Numbers That Matter
Here’s what jumps out from the technical analysis:
Ignition Energy: Hydrogen’s minimum ignition energy is 0.017 mJ compared to 0.28 mJ for methane. That’s 16 times easier to ignite. Your certified electrical equipment? The study explicitly states you must assume ignition will occur anyway.
Flammability Range: 4-75% for hydrogen versus 5-15% for natural gas. This isn’t a minor difference—it’s a 5x wider explosive window that makes inerting strategies far more complex.
Burning Velocity: 3.46 m/s for hydrogen versus 0.45 m/s for methane. Translation: explosions are more severe and can transition to detonation more readily.
Detection Response Time: The study found that conventional point gas detectors respond too slowly. At leak rates as low as 0.1 kg/s, ignitable clouds form within seconds—long before your detection system triggers emergency shutdown.
The Secondary Enclosure Mandate
The EMSA Guidance takes a more conservative position than the draft IMO Interim Guidelines on one critical point: ALL potential hydrogen leak sources should be protected within secondary enclosures—and that explicitly includes piping on open deck, not just enclosed spaces.
Why the stricter approach? Three reasons backed by data:
- Open deck leak detection is challenging. Wind, weather, and rapid dispersion make reliable detection uncertain.
- Critical clouds form faster than detection systems respond. You can’t rely on catching leaks before ignition.
- Industry best practice supports it. Both ISO 15916 and NASA guidelines recommend assuming ignition sources are present.
For compressed hydrogen systems, this means inerted tank connection enclosures with nitrogen or helium. For liquefied hydrogen, it means vacuum-jacketed piping throughout—not just in the tank connection space.
The Reliability Data Gap
Here’s the sobering reality: leak frequency analysis has high uncertainty because we lack maritime-specific hydrogen equipment failure data. The study used generic HCRD and HyRAM+ databases, but neither accounts for ship motion, saltwater corrosion, or limited maintenance access during voyages.
Current estimates suggest one leak event every 10 years for a four-tank compressed hydrogen system—but actual frequencies may be higher given data limitations. Heat exchangers, compressors, and valves are identified as the primary risk drivers.
LH₂’s Cryogenic Challenge
For liquefied hydrogen systems, the study identifies loss of vacuum insulation as a credible event that cannot be excluded from design. At -253°C, hydrogen is cold enough to liquefy air. When vacuum insulation fails:
- External tank surfaces cool below air’s condensation point
- Liquefied air with oxygen enrichment up to 50% forms on ship steel
- Low-temperature embrittlement causes structural damage
- Boil-off rates increase 10-50x normal levels
The guidance requires ships using LH₂ to be designed to safely accommodate vacuum loss—not just detect and respond to it.
The Human Factor
Perhaps most concerning: analysis of 575 hydrogen accidents in the HIAD 2.0 database shows nearly 50% involve human and organizational errors. Safety management system factors account for 49% of incidents, individual human errors for 29%.
This means even perfect technical design isn’t enough. Robust training programs, proper procedures, and active safety culture cultivation are non-negotiable for hydrogen operations.
What This Means for Your Project
If you’re designing or operating a hydrogen-fuelled vessel:
- Budget for secondary enclosures everywhere. This isn’t optional equipment you can value-engineer out.
- Design for substantial leaks. Small leak management won’t cut it—consider up to full-bore rupture.
- Invest heavily in training. Human factors dominate accident causation.
- Plan for data uncertainty. Your risk assessment will have wide confidence intervals until maritime-specific failure data exists.
- For LH₂ projects: design structures for cryogenic exposure. Tank support structure and surrounding ship steel must handle vacuum loss scenarios.
The Bunkering Gap
One significant finding: there’s no harmonized international guidance for shore-side hydrogen bunkering operations. Every port authority and jurisdiction has different requirements, making infrastructure development challenging. EMSA recommends developing comprehensive goal-based bunkering standards—something the industry urgently needs as the hydrogen fleet grows.
Read the Full Technical Analysis
This summary barely scratches the surface. The complete EMSA H-SAFE study includes detailed bowtie analysis for every major hazard scenario, frequency calculations for specific equipment failures, consequence modeling for collision and fire scenarios, and comprehensive guidance spanning 20 chapters.
→ Read our complete deep dive technical analysis covering:
- Detailed reliability analysis with equipment-specific failure rates
- Complete comparison of CH₂ tank connection enclosure configurations
- LH₂ vacuum insulation loss cascade analysis
- Occupational safety hazards and human factors findings
- Paragraph-by-paragraph comparison with IMO draft guidelines
- Comprehensive prescriptive requirements from EMSA Guidance
Industry Implications
The IMO Interim Guidelines are expected for formal approval in 2026. Some flag States and classification societies may adopt the more conservative EMSA approach—particularly in early operational years as experience is gained. Projects currently under construction should review their designs against these findings to identify any gaps.
For the broader industry, this study validates that hydrogen IS viable as marine fuel—but only with purpose-built safety systems that respect its unique properties. The days of “LNG-ready ships with hydrogen capability” are over. It’s time for hydrogen-specific design from the ground up.
Have you encountered design decisions in your project that conflict with these findings? Our comprehensive technical deep dive provides the detailed analysis you need for engineering discussions.
Source
- Study: European Maritime Safety Agency (2025), “Study investigating the safety of hydrogen as fuel on ships,” Final Report, EMSA, Lisbon
- Study Code: EMSA/OP/21/2023
- Publication: November 14, 2025
- Authors: DNV (Linda Hammer, Marius Leisner, Hans Jørgen Johnsrud, Olav Tveit, Torill Grimstad Osberg, Peter Hoffmann)
