Unseen Threats: NIST Uncovers Fire Hazards Lurking Above Electrical Panels

When an electrical panel catches fire, it's rarely a small incident. A circuit breaker failure can rapidly escalate into a multi-compartment blaze, damage nearby cabling, and trigger system-wide failures.

The National Institute of Standards and Technology (NIST) has released a comprehensive technical note - NIST TN 2320 - that examines just how dangerous these fires can become, especially to cable trays mounted directly above enclosures.

This 95-page report is more than a data dump. It should be a wake-up call for you. The research reveals that the thermal effects of even a small enclosure fire can extend upward and outward, threatening equipment not typically considered at risk.

In this blog, we'll walk through NIST's findings. I'll also show you how modern monitoring tools are useful for protecting infrastructure from escalating thermal threats.

The Hidden Dangers of Enclosure Fires

Enclosures used for electrical distribution, such as low-voltage circuit breakers, motor controls, and switchgear, are everywhere - in schools, hospitals, industrial facilities, and power plants. These cabinets often contain a mix of copper, polymeric insulation, panel wiring, and control boards.

When a High Energy Arc Fault (HEAF) occurs inside one of these units, it often sparks intense, long-duration fires. The NIST report documents several real-world configurations: some enclosures burned for over 40 minutes, with sustained flames and internal temperatures exceeding 860 C (1580 F).

What's more alarming is what happens outside the enclosure.

In facility design, overhead cable trays are commonly installed for routing power and communication lines. These trays are often placed 30 to 60 cm above electrical enclosures.

This placement is a standard practice driven by space constraints and layout efficiency. But NIST's experiments show that this placement can turn those trays into unintentional fire propagation pathways.

Even without direct flame contact, the radiant and convective heat from enclosure fires was found to rapidly raise the internal temperatures of overhead cables, leading to:

• Loss of conductor insulation
• Electrical shorting or arcing
• Cable sheath ignition
• Secondary fires in upper trays or rooms

This domino effect puts adjacent systems, and potentially entire facilities, at risk. This is especially risky when early alerts or automated response systems aren't in place.

Passive Protection Isn't Enough

Most fire safety strategies focus on code compliance, insulation ratings, and fire-retardant materials. But those precautions often assume flame exposure is localized and brief.

NIST's findings revealed that many cables ignite purely from thermal exposure, long before a flame ever makes contact. For example:

• Thermoplastic cables ignited in under 2 minutes when placed 36 cm above a 40 kW burner - a conservative stand-in for a burning breaker.
• Tightly packed trays delayed ignition slightly, but once combustion began, the resulting fires were intense and self-sustaining.
• Even thermoset cables, known for higher ignition thresholds, showed signs of failure and scorching, depending on proximity and plume velocity.

In real buildings, these variables - like distance, spacing, and fuel load - vary widely. This means real-time monitoring is the only reliable way to assess when a threat is developing.

The Role of Aluminum "Slugs" in Fire Modeling

A particularly clever feature of the NIST study was the use of aluminum rods ("slug calorimeters") to mimic the heat absorption behavior of real cables. These slugs have similar thermal mass and response times to typical power cables. Plus, they're easier to model and measure with sensors.

Placed alongside actual thermoplastic and thermoset cable segments, the slugs offered consistent, repeatable measurements of how fast heat accumulates above an enclosure fire.

This approach revealed two important things:

1. Internal cable temperatures rise more quickly than many realize. Once the thermal load exceeds ~200 C (392 F), polymer breakdown begins. By 300–400 C, ignition is likely, especially if electrical current or faults are present.
2. Slugs help predict ignition without needing destructive testing. Facilities can now use modeled heat transfer simulations - validated by slug data - to predict fire risk in various enclosure-cable layouts.

For safety engineers and designers, this means fire risk can be assessed and mitigated proactively during design, rather than discovered during a post-incident investigation.

When Fire Growth Outpaces Your Response Plan

Among the more startling findings was how ventilation changes fire behavior. Some of the enclosures tested had pre-existing openings from removed instrument panels or melted plastic. These vent paths allowed more oxygen in, which dramatically increased the heat release rate (HRR).

In one case, covering a previously open vent delayed fire growth. In another, adding panel wire to the upper compartments turned a modest fire into a multi-compartment blaze.

The takeaway here is: fire development inside enclosures is unpredictable and can escalate rapidly once it finds new fuel or airflow.

This creates a major problem for facilities that depend on:

• Visual inspections
• Audible local-only alarms
• Manual detection of equipment overheating

These approaches are slow, inconsistent, and unreliable during off-hours - which is precisely when these fires often go unnoticed.

Digitize Monitoring Platforms Can Help

Digitize systems like the Prism LX address this gap head-on with support for:

• Thermal sensor integration (including slug-like thermocouples)
• Zone-specific alerting
• Relay activation for suppression or alarms
• UL 864-compliant remote reporting

Prism LX lets facility managers monitor cable trays, enclosure zones, and breaker compartments in real time. If temperatures exceed critical thresholds - even before visible fire appears - the system can:

• Trigger alerts via text or email
• Log events to support post-incident analysis
• Activate ventilation or suppression relays
• Notify off-site command centers instantly

This functionality is especially useful for critical facilities like:

• Power substations and switchyards
• Data centers and control rooms
• Transit depots and airport infrastructure
• Industrial automation cabinets
• Nuclear or military facilities (like those studied by NIST)

Retrofit Without Ripping Out

One of the biggest concerns facility managers face is cost. Pricing is especially a concern when fire system upgrades are perceived as requiring total infrastructure replacement.

But the beauty of the Prism LX is that it's designed for backward compatibility. Rather than tearing out old breaker panels or rewiring the entire building, you can:

• Use interface modules to capture inputs from legacy equipment
• Connect standalone sensors to critical zones
• Set custom thresholds for specific components or zones
• Rely on redundant power paths and failover units to ensure 24/7 uptime

That means you get predictive insight and compliance-grade monitoring without swapping out a ton of equipment.

Thermal Ignition Timelines: Measured and Predictable

Let's dive into some quantitative highlights from the NIST report:

Test #	Cable Type	Mounting Height	Ignition Time
36	Thermoplastic	36 cm	1:30 min
37	Thermoplastic	56 cm	4:00 min
39	Thermoset	36 cm	1:30 min
45	Thermoset (dense pack)	36 cm	50:00 min (minor ignition only)
46	Thermoset	36 cm	12:00 min
47	Thermoplastic	36 cm	<1:00 min
48	Thermoplastic	56 cm	3:00 min

As the data shows, packing density, cable composition, and proximity all influence ignition. The danger zone consistently begins within the first 1 to 5 minutes of exposure.

Take a Modern Approach to Fire Planning

This kind of timeline is far too short for anything but an automated monitoring system. By the time someone notices smoke, the internal temperatures may already have exceeded critical limits. And once ignition occurs, fire can spread along cable trays, into junction boxes, or up vertical risers.

This is why modern fire response must be automated and predictive, not reactive.

Digitize platforms help you make this shift by:

• Integrating with real-world fire data
• Monitoring thermal conditions near high-risk enclosures
• Alerting facilities before ignition thresholds are crossed
• Providing data to inform future design or retrofits

When paired with detailed sensor layouts and cable tray mapping, this approach can turn your building into a self-aware safety environment.

Don't Wait for a Crisis to Reveal the Gaps

NIST's report offers a critical reminder: electrical fires don't stay contained. They radiate heat, ignite secondary systems, and spread through pathways we often overlook.

The real risk lies in failing to see the big picture - and failing to monitor it in real time.

Digitize is here to help you connect the dots from physical risk to predictive insight.

Take the Next Step Toward Intelligent Fire Safety

If you're overseeing electrical safety in a complex facility, the time to act is now. Fires don't wait. Neither should your monitoring strategy.

Call Digitize at 1-800-523-7232
Or email info@digitize-inc.com

Ask how Prism LX and related tools can turn the latest fire science into real-world protection for your facility.