Fired Heater Tube Rupture and Fire
Marathon Martinez Renewable Fuels Fire
Marathon Martinez Renewables / Marathon Petroleum Corp.
📍 Martinez, CA
Incident: November 19, 2023  •  CSB Report: March 13, 2025
0
Fatalities
8
CSB Recommendations
📋 Incident Summary

On November 19, 2023, a fired heater tube ruptured in the Hydrodeoxygenation (HDO) Unit recycle furnace at Marathon Martinez Renewables in Martinez, California. The rupture released flammable process fluids that ignited, seriously burning one operator. The Martinez facility is a converted refinery re-engineered to produce renewable diesel from plant-based feedstocks under high temperature and pressure.

The CSB found multiple contributing factors. The fired heater experienced 'afterburning' -- combustion in the convection section rather than the firebox -- which dramatically elevated tube metal temperatures. No instrumentation existed to detect afterburning, and no tube metal temperature alarms were in place. A walk-the-line failure left a valve misaligned from a prior operation, diverting process flow away from the heater and creating a low-flow condition that worsened tube overheating. No alarm detected the diverted flow.

The CSB's final report, released March 13, 2025, issued eight recommendations covering afterburning detection, tube metal temperature alarming, Walk the Line improvements, and corporate standard revisions. One recommendation to implement afterburning safeguards at the specific heater has been closed as completed.

🔎 Key Findings
Finding 1
Afterburning Caused Tube Overheating
Combustion in the convection section of the fired heater (afterburning) raised tube metal temperatures far beyond safe limits. Afterburning is a known hazard in fired heaters, but no safeguard existed to detect it.
Finding 2
No Tube Metal Temperature Alarms
No alarm system existed to alert operators when tube metal temperatures exceeded safe limits. The developing overtemperature condition was invisible to operators until tube rupture occurred.
Finding 3
Walk-the-Line Failure -- Diverted Flow
A valve was left misaligned from a prior operation, diverting process flow away from the fired heater tube. The resulting low-flow condition removed cooling to the tubes, worsening the overtemperature.
Finding 4
No Low-Flow Detection for Diverted Flow
No instrumentation or alarm detected diverted flow downstream of the flow meter. Loss of process flow through the heater was not detected before tube failure.
Finding 5
Safe Operating Limits Not Enforced
The facility lacked alarm and shutdown systems to alert operators and trigger predetermined responses when tube metal temperature safe operating limits were exceeded.
Finding 6
Gap Between Site and Corporate Standards
A comprehensive gap assessment had not been performed to confirm the Martinez facility was fully implementing Marathon Petroleum Corporation's corporate policies for process safety and fired heater operation.
🔍 Root Causes
1
Afterburning Undetected and Unaddressed
No safeguard existed to detect afterburning in the fired heater. Afterburning is a recognized cause of tube overtemperature failure and requires specific engineering controls.
2
No Tube Metal Temperature Alarming
Without tube metal temperature alarms, operators had no automated warning of the developing failure condition. Predetermined shutdown and evacuation actions require prior alarm notification.
3
Walk-the-Line Procedure Deficiencies
The Walk the Line process did not catch the misaligned valve. Effective pre-startup valve lineup verification is a critical safeguard against low-flow and misdirected flow conditions.
4
Corporate Standard Did Not Require Low-Flow Protection
The corporate Heater Application Standard did not require safeguards for scenarios where process piping diverges downstream of a flow meter -- a configuration that creates low-flow risk to the heater.
☑ CSB Recommendations
→ Marathon Martinez Renewables
Implement engineering safeguards to detect and prevent afterburning in the fired heater involved in the November 2023 incident. [STATUS: CLOSED -- Acceptable Action Implemented]
→ Marathon Martinez Renewables
After the corporate tube metal temperature alarming standard is updated, implement alarming consistent with corporate guidance to alert operators when safe operating limits are exceeded and specify predetermined response actions including heater shutdown.
→ Marathon Martinez Renewables
Improve Walk the Line performance by requiring documented valve line-up verification before all unit startups and ensuring abnormal line-ups are communicated across shifts.
→ Marathon Martinez Renewables
Complete a comprehensive gap assessment of the Martinez facility against all applicable Marathon Petroleum Corporation policies, including Operating Limits, PHA, and PSM/RMP Operating Procedures.
→ Marathon Petroleum Corporation
Update the corporate 'Process Heater Not-to-Exceed (NTE) Limits and Alarms' standard with tube metal temperature alarming guidance and predetermined response actions including shutdown and personnel removal.
→ Marathon Petroleum Corporation
Update the corporate 'Heater Application Standard' with requirements for low-flow protection where piping diverges downstream of flow meters and engineering safeguards for afterburning detection.
→ Marathon Petroleum Corporation
Confirm gap assessment results from the Martinez facility and conduct an Operations Excellence full assessment. Develop and implement corrective action items.
→ American Petroleum Institute (API)
Revise API RP 556 to include requirements for tube metal temperature alarming, low-flow protection for heaters, and engineering safeguards for afterburning detection.
💡 Lessons Learned
⚠ Safe Operating Limits for fired heaters must include tube metal temperature limits with automated alarms. Without alarming, exceeding the limit is invisible to operators until the tube fails.
⚠ Afterburning in a fired heater is a known and documented hazard that requires specific instrumentation to detect. Its absence from a standard safeguard list does not mean it cannot occur.
⚠ Walk the Line is the last verification before process flow restores energy to a heater. A missed valve misalignment during Walk the Line can create the exact low-flow conditions that rupture tubes.
⚠ When a corporate engineering standard lacks a safety requirement, that gap exists at every facility using that standard. Corporate standard deficiencies can create fleet-wide hazards simultaneously.
⚠ Predetermined response actions -- including 'shut down and evacuate' -- must be defined before an abnormal condition develops. Operators should not be formulating the response plan when tube metal temperatures are already at the alarm threshold.
PSM Elements: SOP · PHA · MI · TRN
🔨 Safety Meeting Toolbox Talk
Topic: Fired Heater Safety and Safe Operating Limits
💬Do the fired heaters in our facility have tube metal temperature monitoring and alarms? What is the predetermined response action when a tube metal temperature alarm is triggered?
💬What is 'afterburning' in a fired heater, and does our process have safeguards to detect it -- such as combustibles measurements, convection section thermocouples, or flame detectors?
💬How do we perform Walk the Line at this facility? Who verifies valve alignment before heater startup, and is there a documented sign-off for the lineup?
💬Are there any branch connections downstream of flow meters in our process where diverted flow would not be detected by the upstream flow indicator?
💬What are the Safe Operating Limits for the fired heaters in our unit? Are those limits posted in the control room and do operators know the predetermined response for each alarm?
💬When did our facility last conduct a gap assessment against corporate engineering and PSM standards? Were fired heater safeguards specifically evaluated?
✎ Team Action Items
✓Review tube metal temperature monitoring and alarm setpoints for fired heaters in your area -- verify alarms are functional and confirm the documented response action for each
✓Review the Walk the Line procedure for your unit -- verify it requires a documented valve alignment check before every heater startup, including restarts from non-routine shutdowns
✓Identify any branch connections downstream of flow meters in your fired heater system and verify that low-flow scenarios have been evaluated in the PHA
✓Confirm that Safe Operating Limits for fired heaters are posted and current -- verify all operators know the limits and response actions for each alarm
🔗 PSM Failures Behind This Incident

This incident traced to breakdowns across 4 PSM elements (SOP · PHA · MI · TRN). Each represents a documented gap that process safety documentation and consulting can close before a similar event occurs at your facility.

Operating Procedures (SOPs)
Operators cannot reliably hold safe operating limits without clear, current, enforced procedures. Deviation from acceptable operating conditions — a root cause here — is a direct consequence of SOP failure.
Supporting documents in our library →
Process Hazard Analysis (PHA)
A structured PHA or HAZOP study exists to identify exactly these scenarios before they occur. When PHA is absent, superficial, or overdue for revalidation, hazards operate unseen until they kill someone.
Supporting documents in our library →
Mechanical Integrity (MI)
Equipment must be designed, inspected, and maintained to operate safely in its intended service. Mechanical integrity failures — degraded equipment, missed inspections, deferred repairs — contributed to loss of containment here.
Supporting documents in our library →
Training & Operator Competency
Workers must understand process hazards — not just the steps on the page. Training records, refresher frequency, and verified competency are all OSHA PSM requirements that gaps here violated.
Supporting documents in our library →
Process Safety Management Consulting & Document Library
📂
PSM Document Library
32 ready-to-deploy PSM documents covering all 14 OSHA elements — procedures, checklists, and audit templates built for facilities operating under 29 CFR 1910.119.
Browse the Library →
📊
Free PSM Health Score
Find out where your PSM program stands across all 14 OSHA elements. Our free health score surfaces your biggest gaps in under 10 minutes — no account required.
Check Your Score →
📞
Consulting Services
PHA facilitation, PSM program builds, compliance audits, and OSHA inspection support. Transparent flat-fee pricing — no retainer required to get started.
View Pricing →
📋 Explore the full incident library: All 132 CSB Case Studies →