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Introduction
From September 18 to October 2, 2025, Technical Safety BC shared a draft fault tree to visualize different failure scenarios that can lead to an uncontrolled release of ammonia from ammonia refrigeration systems. We collaborated with the refrigeration industry to improve the quality of this draft fault tree. This report summarizes what we heard from the participants who provided feedback on the draft fault tree.
Outreach and participation
We distributed an email to more than 250 recipients, including refrigeration system owners, contractors, and power engineers. We invited them to review the draft fault tree, identify areas requiring clarification, and suggest additional scenarios that may have been missing. Feedback was collected through an online survey and a virtual workshop.
The following table summarizes the number of participants in these engagement activities.
Participation method |
Number of participants |
Survey respondents |
6 |
Virtual workshop participants |
3 |
Webpage visitors |
52 |
Downloads of the draft fault tree |
32 |
The following table summarizes the types of participants who responded to the survey.
Client type |
Number of participants |
Contractor |
4 |
Power engineer |
1 |
Facility owner/manager representative |
1 |
Summary of Responses
Participants in the survey and virtual workshop contributed their expertise to identify areas missing from the failure scenarios.
Survey
All survey respondents found the fault tree to be clear. 50% of the survey participants answered that the fault tree had missing scenarios with two participants detailing the missing branches.
Virtual workshop
On October 8, 2025, we hosted a virtual workshop with three participants to discuss the missing failure scenarios. We worked together on how best to integrate them into the tree.
Resulting changes
The following table summarizes changes to the fault tree as a result of the discussions.
Fault Tree Basic Condition |
Updates to Failure Scenarios |
Branch References |
Pressure boundary failure |
Added a branch to address issues with valve oil levels |
A-25
|
|
Added examples to the “physical impact” branch |
A-30 |
|
Added two branches under “mechanical damage” to account for vibration and poor support conditions |
A-33, A-34 |
|
Added branches to address isolating equipment without proper purging procedures and consideration for unprotected and isolated areas |
A-44, A-48, A-51 |
|
Added branches to address sub-optimal operational conditions (i.e. presence of non-condensables and overcharged systems) |
A-52, A-53, A-54 |
Intentional opening of system |
Added a branch to address vandalism of the system |
D-58 |
Uncontrolled release through relief valve |
Added branches to address failed pressure limiting devices and intentional and unintentional override |
E-33, E-34, E-35, E-36 |
Participants also suggested modifying the fault tree layout to read from left to right. For consistency with existing Technical Safety BC fault trees, we decided to keep the current layout.
Next Steps
The final version of this fault tree is now available for download. This fault tree will serve as a critical component in our ammonia release risk analysis that will identify predominant scenarios of ammonia release. Understanding these predominant scenarios will help shape risk treatment actions effectively. Risk treatment planning for ammonia release is currently scheduled for early 2026. As part of this initiative, we will further engage with industry to assess existing risk treatment actions and develop new risk treatment actions.
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As part of a comprehensive ammonia risk analysis, Technical Safety BC has drafted a fault tree to visualize different failure scenarios that can result in the uncontrolled release of ammonia from ammonia refrigeration systems. This fault tree is foundational for characterizing each ammonia incident in BC and helps us identify the most prominent scenarios to be addressed through our risk treatment plan. We would like industry's help to clarify and add any missing scenarios to this fault tree. The risk treatment planning process is scheduled for early 2026 and will reconsider existing actions and develop new risk treatment actions with industry experts to tackle the risk of ammonia release in BC.
We invite you to share your expertise by taking the survey (deadline: October 2, 2025, 5 pm) to help improve this fault tree.
If you are interested in attending a workshop on October 6, 2025 or October 8, 2025 to discuss any missing scenarios, please save these dates. Workshop registration can be completed at the end of the survey.
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