Hydrogen Risk Assessment Model (HyRAM)

The HyRAM toolkit is the first-ever software toolkit that integrates deterministic and probabilistic models for quantifying accident scenarios, predicting physical effects, and characterizing hydrogen hazards’ impact on people and structures. HyRAM incorporates generic probabilities for equipment failures and probabilistic models for heat-flux impact on humans and structures, with computationally and experimentally validated models of hydrogen release and flame physics.

The initial modules can be used to quantify the likelihood and thermal consequences associated with gaseous hydrogen releases from user-defined hydrogen installations. Future development activities will integrate additional consequence models and develop user interfaces for additional audiences. When completed, the toolkit will enable industry-, SDOs (standards development organizations)-, and CDO (code development organizations)-led quantitative risk assessment and performance-based engineering with state-of-the-art, validated science and engineering models.

The HyRAM software is available under an open source license.

Access the source code for HyRAM via GitHub

Download the most recent build of the Windows-only installer

Note: please completely uninstall any previous versions of HyRAM before installing.


Developing hydrogen codes and standards is challenging because the relevant models and information span multiple science and engineering disciplines. The HyRAM toolkit integrates state-of-the-art models and data for assessing hydrogen safety. HyRAM provides a common platform for stakeholders conducting quantitative risk assessment and consequence analysis for hydrogen systems. The resulting information provides the scientific basis to ensure code requirements are consistent, logical, and defensible.

  • Generic data for gaseous hydrogen (GH2) systems:
    component leak frequencies, ignition probability; modifiable by users
  • Models of GH2 physical effects for consequence modeling
    • Release characteristics (plumes, accumulation)
    • Flame properties ( jet fires, deflagration within enclosures)
  • Probabilistic models for human harm from thermal and overpressure hazards
  • Fast running: to accommodate rapid iteration
  • Calculates common risk metrics for user-defined systems:
    FAR, AIR, PLL; frequency of fires
  • Ongoing development activities to add liquid hydrogen systems and features to add usability
  • QRA and consequence calculations used to inform GH2 separation distances (NFPA 2, 2008)
  • QRA results used to inform indoor fueling requirements (NFPA 2, 2011)
  • Developed performance-based framework for establishing safety distances & mitigations (NFPA 2, 2016 and ISO TR-19880)
  • Ongoing activities: Liquid hydrogen separation distance
  • Future opportunities: Evacuation zone analysis, enclosure risk modeling



Risk Metric Value
PLL 7.362e-05
FAR 0.0168
AIR 3.362e-07
Scenario End State Type Avg. Events/Year
100pct Release No Ignition 0.0008
10pct Release No Ignition 0.0012
1pct Release No Ignition 0.0015
0.1pct Release No Ignition 0.0050
0.01pct Release No Ignition 0.0348

Sample HyRAM output: plots of jet flame temperature and heat flux for user-defined hydrogen releases; PLL, FAR, AIR, and frequency of unignited releases from a user-defined hydrogen installation

Given a user-defined system, risk analysts can use HyRAM to answer the following types of questions:

  • How would changes to system design affect overall risk?
  • Which design is the safest?
  • Will this enhance system safety? (If used with an economic model: is the increase in system cost justified?)
  • What is the likelihood of a release from an installation?
  • How likely is it that a jet fire or deflagration would occur?
  • What is the heat flux from a jet flame associated with a specific hydrogen release?
  • At what distance does heat flux reach the no-harm threshold?
  • Documentation

    Suggested citation for HyRAM 3.1.0: Brian D. Ehrhart, Cianan Sims, Ethan Hecht, Alice B. Muna, Katrina M. Groth, John T. Reynolds, Myra L. Blaylock, Erin Carrier, Isaac W. Ekoto, and Gregory W. Walkup. HyRAM (Hydrogen Risk Assessment Models), Version 3.1.0. Sandia National Laboratories (May 11, 2021); software available at https://hyram.sandia.gov.

    HyRAM 3.1 Technical Reference Manual. Brian D. Ehrhart and Ethan S. Hecht. Hydrogen Risk Assessment Models (HyRAM) Version 3.1 Technical Reference Manual. SAND2021-5812. May 2021.

    HyRAM Validation Report. Brian D. Ehrhart, Ethan S. Hecht, and Jamal A. Mohmand. Validation and Comparison of HyRAM Physics Models. SAND2021-5811. May 2021.

    HyRAM 2.0 User Guide. Guillermo Feliciano Morales, Brian D. Ehrhart, and Alice B. Muna. HyRAM V2.0 User Guide. SAND2019-8940. July 2019.

    We recommend including the full version number (e.g. HyRAM 2.0.0) in your work. The version number can be found in HyRAM on Help/About HyRAM.

  • HyRAM 3.0 Technical Reference Manual. Brian D. Ehrhart and Ethan S. Hecht. Hydrogen Risk Assessment Models (HyRAM) Version 3.0 Technical Reference Manual. SAND2020-10600. September 2020.
  • HyRAM 1.1 Technical Reference Manual. KM Groth, ES Hecht, JT Reynolds, ML Blaylock, EE Carrier. Methodology for assessing the safety of Hydrogen Systems: HyRAM 1.1 Technical Reference Manual. SAND2017-2998. March 2017
  • Suggested citation for HyRAM 1.1: Katrina M. Groth, Ethan Hecht, John T. Reynolds, Myra L. Blaylock, Erin Carrier HyRAM (Hydrogen Risk Assessment Models), Version 1.1. Sandia National Laboratories, (2/28/2017); software available at http://hyram.sandia.gov
  • Suggested citation for HyRAM 1.0: Katrina M. Groth, Ethan Hecht, John T. Reynolds, Myra L. Blaylock, Isaac W. Ekoto, and Gregory W. Walkup (2016). HyRAM (Hydrogen Risk Assessment Models), Version 1.0. Sandia National Laboratories, 2016; software available at http://hyram.sandia.gov.
  • HyRAM 1.1 User guide. Ethan A. Sena, Brian D. Ehrhart & Alice B. Muna. HyRAM V1.1 User Guide. SAND2018-0749, Sandia National Laboratories, Albuquerque, NM, January 2018.
  • HyRAM 1.0 Technical reference manual. Katrina M. Groth, Ethan S. Hecht & John T. Reynolds. Methodology for assessing the safety of Hydrogen Systems: HyRAM 1.0 technical reference manual. SAND2015-10216, Sandia National Laboratories, Albuquerque, NM, November 2015.
  • HyRAM 1.0 User guide. Katrina M. Groth, Hannah R. Zumwalt & Andrew J. Clark. HyRAM V1.0 User Guide. SAND2016-3385 R, Sandia National Laboratories, Albuquerque, NM, March 2016.
  • HyRAM overview webinar and slides.
  • HyRAM Discussion Forum on H2Tools
  • Conference Papers:
  • Brian Ehrhart
    HyRAM Team Lead
    (505) 284-4906

    Ethan Hecht
    Hydrogen Behavior Expert
    (925) 294-3741

    Chris LaFleur
    Hydrogen Safety Codes and Standards Manager
    (505) 844-5425

    Sandia’s Hydrogen Program supports the nation’s energy strategy—helping to diversify America’s energy sector and reduce our dependence on foreign oil through the advancement of hydrogen and fuel cell technologies. HyRAM is developed for the U.S. Department of Energy Hydrogen and Fuel Cell Technologies Office by Sandia National Laboratories.