In the natural gas industry, emergencies don’t occur during optimal conditions. They happen in the middle of the night, on the weekend, and when it’s freezing cold outside.  Whether it’s a main break, third-party damage, or a detected leak, knowing exactly which valves to close and which customers will be affected is not just a convenience; it’s a critical component of safety and operational efficiency. GIS is no longer just a mapping tool; it’s a critical decision support system, and GIS professionals are often the first line of support for operations and emergency response teams.  That’s where a well-structured GIS isolation subnetwork and custom valve isolation tracing come into play.

What Is an Isolation Subnetwork?

An Isolation subnetwork represents the portion of a gas network that can be isolated using specific control devices, typically emergency valves. These subnetworks are crucial in emergency response, planned outages, and routine maintenance. When properly configured, they allow you to quickly trace the gas network and determine which customers, mains, or facilities would be affected if a given valve is closed.  For example, during a reported gas leak, an operator can run a trace from the nearest emergency valve(s) to determine how much of the network will be shut off and who will be affected. This accelerates both the decision-making process and emergency response.

Core Components of a Natural Gas Isolation Subnetwork

When configuring an Isolation subnetwork in the Utility Network for gas, the following components are essential:

1. Subnetwork Controllers

In the gas model, emergency valves are designated as subnetwork controllers. These devices define where an isolation zone begins and ends. They must be correctly classified using asset groups and types and set with the proper controller role.

2. Subnetwork Tier: Isolation

In your gas domain network, the Isolation tier defines how gas can be segmented and isolated. This tier sits alongside others like Pressure and Cathodic Protection, but serves its own distinct operational purpose.  Your tier definition includes:  Valid asset types (valves), terminals (inlet/outlet for different isolation zones), and trace configuration and rules such as starting points, barriers, traversability conditions and returned results.

3. Asset Groups & Asset Types

For Device features to participate in an Isolation subnetwork, they must be accurately placed into Asset Groups and Asset Types:
Pipeline Device → Asset Group: Controllable Valve → Asset Type: Emergency Valve

4. Terminal Configuration

Each valve must have the correct terminal configuration to reflect real-world connections. This ensures accurate tracing through devices and proper network validation. For large-scale deployments or schema setup, batch loading allows you to establish multiple terminal configurations at once using tools like ‘Import Terminal Configurations’ from pre-defined spreadsheets or XML files.  Terminal configurations can also be added manually through the ArcGIS Pro interface, which is ideal for custom configurations, testing, or refining individual network elements.

5. Subnetwork Naming and Updating

Each isolation zone can be named based on your configuration and data (“Zone_5_West”, “Zone12345”) and updated using the Update Subnetwork geoprocessing tool. These names support labeling, trace analysis, and reporting.

Benefits of Modeling Isolation Subnetworks

Fast Emergency Response – Time is everything during a gas emergency.  Which valves do we need to shut? Which customers will lose service?  How fast can we isolate this section?  A complete subnetwork allows GIS analysts and field crews to run real-time traces that immediately identify which valves are needed to isolate a section. No guesswork, no delays.

Customer Impact Awareness – By tracing upstream and downstream from the incident location, operators can also see which customers will be impacted by the shutoff. This level of visibility improves communications with customer service teams, field personnel, and even emergency responders.

Field-Ready Maps and Mobile Integration – A fully operational isolation subnetwork means you can generate valve isolation maps and work packages on the fly. When integrated with mobile GIS tools, these can be dispatched directly to field crews instantly with no lag time.

Training and Preparedness Drills – Emergency response isn’t just about reacting, it’s also about preparing. GIS professionals can support operations training by creating realistic emergency scenarios. Simulated traces help train new staff, validate operating procedures, and prepare for regulatory audits. With live data integration, GIS-based simulations become powerful planning assets.

Regulatory and Audit Support – Having a documented procedure for valve isolation supports regulatory compliance and post-event audits. It shows that you have a proactive, systematic approach to safety and emergency planning.

Custom Valve Isolation Tracing: The Real Game-Changer

Out-of-the-box tracing tools are helpful, but custom-built valve isolation traces bring the functionality to the next level. Tailored to your network’s real-world logic, these traces can:

• Prioritize valves based on accessibility (valve boxes)
• Define standard barriers such as closed valves or reg stations
• Automatically include critical facilities unless flagged
• Provide multi-scenario options (manually placed squeeze points)
• Return not just isolated mains, but affected services and customer meters

With custom tracing, GIS becomes more than a map, it becomes a decision-making engine.

If your company’s GIS data quality isn’t ready to support building a reliable isolation subnetwork (disconnected features, inaccurate valve status, missing attributes), there are still several actionable steps you can take to move toward operational readiness.

1. Launch a Focused Data Improvement Initiative

What to do:

• Prioritize areas with high customer density or critical infrastructure.
• Perform targeted QA/QC to update and connect gas mains, valves, and services.
• Leverage existing as-built drawings, field notes, and valve cards to enhance attribution.

Why it matters: You don’t need perfect data everywhere, so start where it counts most.

2. Use Partial or Simplified Tracing Models

What to do:

• Build “pseudo-subnetworks” using basic topology rules (trace from incident point upstream/downstream without relying on full subnetwork controller logic).
• Use buffers or proximity tools to approximate customer impact.

Why it matters: Even without a full subnetwork model, simplified tools can still provide actionable insights during emergencies.

3. Integrate Field Verification into Maintenance Workflows

What to do:

• Equip field crews with mobile GIS apps to collect missing valve data (open/closed, valve box present).
• Use valve inspection and leak survey programs to opportunistically validate and correct GIS features.

Why it matters: Data improvement becomes part of daily operations instead of a one-off project.

4. Develop a Trace-Ready “Pilot Area”

What to do:

• Identify one well-documented part of the system and build out a fully connected, trace-enabled subnetwork there.
• Use this area for training, demonstrating value, and benchmarking improvements.

Why it matters: Proving the value of tracing in one area builds the case for broader investment.

5. Establish Data Governance and Standards

What to do:

• Create documentation on required data fields for valves, mains, and services
• Enforce rules for how new construction gets added to GIS, including traceability.

Why it matters: Good data starts with clear expectations and accountability.

6. Work with Operations to Build “Valve Isolation Playbooks”

What to do:

• Even without GIS automation, collaborate with operations to document common shutoff scenarios and create maps or look-up tables.
• Later, these can be built into formal GIS tools when data quality improves.

Why it matters: Why it matters: Your GIS can still support response planning even with static or semi-manual tools.

Wrapping Up

Building and maintaining an isolation subnetwork in your gas GIS is no small feat. It takes collaboration between GIS, field engineers, and operations teams, but the payoff is huge: faster responses, better communication, and safer communities.  GIS professionals have the skills and tools to be key players in emergency response, not just after the fact but in the moment. A well-maintained isolation subnetwork, along with intelligent valve tracing tools can reduce response times, support safer operations, and garner trust across the company.