In the rapidly evolving hydrogen industry, safety codes and standards are struggling to keep pace with new technology advancements and increases in historical pressure and flow rates. Today’s codes and standards are advancing as well, but contradictions and gaps pose challenges for hydrogen users.

One area where this gap is particularly evident is in ventilation requirements for hydrogen systems.

This article explores the issues around hydrogen ventilation with Dr. Danielle “Dani” Murphy, Principal Engineer and Hydrogen Services Lead, and Dr. Harold Beeson, Principal Chemist at WHA.

Why Ventilate Hydrogen Systems?

Ventilation is critical for the safe storage and use of hydrogen. Whether passive or mechanical, ventilation enables released hydrogen to dilute in the surrounding air to prevent or limit the formation of combustible mixtures.

Determining appropriate methods and rates for ventilation is where things get complicated.

Current Key Hydrogen Ventilation Standards

Several standards already exist for hydrogen ventilation, but none of them provide a complete picture of the issue. They may address a few factors, but they don’t account for all the system-specific variables like pressure, pipe size, component count, leak susceptibility and rate, or the configuration of the space.

Area-Based Guidance

NFPA 2, National Hydrogen Technologies Code (2023) requires, “Mechanical exhaust or fixed natural ventilation shall be provided at a rate of not less than 1 scf/min/ft² (0.0051 m³/sec/m²) of floor area over the area of storage or use.” This approach only considers floor area, not enclosure/building volume, system pressure, hydrogen inventory, or potential leak scenarios. A similar area-based approach is shared by other codes, including:

• NFPA 55, Compressed Gases and Cryogenic Fluids Code
• Factory Mutual (FM) Global Data Sheet 7-91, Hydrogen
• United States International Fire Code (IFC) Chapter 50, 5004.3.1.
• European Industrial Gases Association (EIGA) 15/21

Dilution-Based Standards

Other common codes state that ventilation should be sufficient to dilute leaks to 25% of the lower flammability limit (LFL), equivalent to a hydrogen concentration of 1% volume. This end goal may be appropriate, but the standards are still missing half of the equation: what is the size of a credible leak, and how long will the leak persist? 

This approach also does not consider the fact that bulk averaging to establish concentration does not consider the combustion hazard in the vicinity of the leak.

 Standards referencing LFL include:

• U.S. Code of Federal Regulations (29 CFR 1910.106)
• ISO 19880-1, Gaseous hydrogen – Fueling stations
• NFPA 69, Standard on Explosion Prevention Systems
• ISO 22734, Hydrogen generators using water electrolysis
• IEC 60079-10-1, Classification of areas – Explosive gas atmospheres
• Occupational Safety and Health Standards Confined Spaces Standard – 29 CFR 1910.146
• NFPA 497, Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas

Limitations of the Checkbox Mentality

A concerning trend, especially in North America, is the tendency to treat codes and standards as prescriptive checkboxes rather than starting points for comprehensive safety analysis.

This approach can create a dangerous false sense of security. The minimum ventilation rates specified in many codes, often resulting in just 4 to 10 air changes per hour, may be woefully inadequate for modern high-pressure hydrogen applications.

“Checking a box in codes cannot guarantee safety. A thoughtful analysis of your specific system, its potential failure modes, and appropriate mitigation strategies is essential for ensuring safety in hydrogen applications.” – Dr. Harold Beeson, Principal Chemist

The Missing Piece: Credible Leak Rates

At the heart of the ventilation challenge is a fundamental question: What is a “credible” leak rate for a given hydrogen system?

The concept refers to what kind of leak is probabilistically expected in a well-maintained system, not catastrophic failures, which typically require different mitigation strategies and are not expected to be mitigated by ventilation.

That guidance is also all over the map for hydrogen—sometimes orders of magnitude different from one source to the next.

1. NFPA 2 (National Fire Protection Association) uses historical oil and gas frequency and leak rate data to establish prescriptive outdoor setback distances based on internal flow area of the largest pipe size in the system.
2. CGA TR7 (Compressed Gas Association) for nontoxic cryogenic systems takes a more comprehensive approach by counting the number, type, and size of components and length and size of piping in the system to assess annualized failure rate.
3. IEC 60079-10-1 provides methods to estimate release rates but isn’t specific to hydrogen or hydrogen applications.

The lack of hydrogen-specific leak rate data is a significant gap in the industry’s knowledge base.

“The industry simply doesn’t have statistically relevant fundamental failure data to accurately inform ‘credible leak rate’ estimates for today’s hydrogen applications.” – Dr. Danielle “Dani” Murphy, Principal Engineer and Hydrogen Services Lead

Time Considerations in Ventilation Effectiveness

Another often overlooked aspect of ventilation is the time dimension. Ventilation doesn’t provide immediate protection against leaks but rather helps dilute concentrations over time.

For any leak, the size and concentration of the flammable gas cloud will increase until reaching a steady state based on the size of the leak and ventilation flow rate. The hazard will continue until the source has been isolated and the remaining gas has been removed from the system.

Best Practices for Hydrogen Ventilation

Given the limitations of current standards, what should organizations do to ensure adequate ventilation for hydrogen systems? Dr. Murphy offers several recommendations:

1. Do not treat minimum ventilation rates as inherently safe. “The minimum ventilation is just that: the minimum. In many cases, even considering other safety controls and mitigations like detection and automatic shutdown, the minimum ventilation rates are insufficient to prevent accumulation.”
2. Consider your specific scenario. “A holistic risk-based approach to safety is always preferred. You need to be thinking about credible release scenarios and all risk mitigators, along with their associated effectiveness, to establish an appropriate ventilation rate for your system and your risk tolerance. “
3. Evaluate your layers of protection. “Do you have multiple detectors? How much time delay is expected to shut down? How much volume do you have in the space that could potentially leak? What does safe isolation look like? These are all important considerations.”
4. Take a holistic approach to safety. “If you’re going to put hydrogen in an enclosure, you better have multiple layers of protection beyond ventilation. And ventilation cannot prevent the issue in the first place—that comes back to the fundamental best practices for hydrogen system design.”

How WHA Helps Navigate Ventilation Challenges

WHA International takes a comprehensive approach to helping clients determine appropriate ventilation requirements for their hydrogen systems:

The process typically involves:

1. Conducting a design review to identify layers of protection
2. Calculating multiple potential leak rates based on different methodologies
3. Performing ventilation calculations for the specific enclosure
4. Developing transient data plots showing how hydrogen concentrations would change over time
5. Providing information to help clients make risk-based decisions

“We look at ventilation from a performance-based, holistic approach. We help clients understand best practices based on their systems, their layers of protection, and their risk tolerance.” – Dr. Harold Beeson, Principal Chemist

The Path Forward

The hydrogen industry is actively working to address the gaps in ventilation standards.

Recently, the Hydrogen Safety Panel has developed a white paper on ventilation considerations with WHA’s Dr. Dani Murphy and Dr. Harold Beeson. White Paper PNNL-37333: “Considerations for Ventilation Rates to Mitigate Hydrogen Releases” highlights the variation in current codes and calls for more research and standardization.

Read the white paper (Available for CHS Members)

The rapid growth of the hydrogen economy has created significant challenges for safety standards, particularly in the area of ventilation. While the industry works to develop more comprehensive and consistent guidelines, organizations must take a proactive approach to safety that goes beyond minimum code requirements.

By understanding the limitations of current standards and taking a risk-based approach to ventilation design, organizations can help ensure the safe deployment of hydrogen technologies across a wide range of applications.