Tesoro Martinez Refinery Sulfuric Acid Spill

📋 Incident Summary

On February 12, 2014, approximately 84,000 pounds of concentrated sulfuric acid was released at the Tesoro refinery in Martinez, California, burning two workers who suffered first and second degree acid burns. A compression fitting at a sulfuric acid sampling station had been inadequately tightened during a recent maintenance activity, and the fitting failed under the acid line operating pressure, releasing the highly corrosive liquid. The incident was not the first — Tesoro Martinez had experienced 15 separate sulfuric acid spills in the five years preceding this event.

The pattern of 15 acid spills in five years demonstrates a systemic failure in the management of sulfuric acid hazards at the refinery. The CSB found that Tesoro had not investigated the causes of prior acid spills as precursor events requiring corrective action. Compression fittings on sulfuric acid lines had been identified as a maintenance problem in prior events, but no systematic engineering review or fitting replacement program had been implemented.

The CSB investigation was complicated by Tesoro initial refusal to allow CSB investigators access to the incident site and evidence. The CSB noted that this obstruction delayed the investigation and raised concerns about the broader safety culture at the facility. The CSB ultimately issued six recommendations targeting both the technical failures and the management culture deficiencies at Tesoro Martinez.

🔎 Key Findings

Finding 1

15 Acid Spills in 5 Years Before This Incident

Tesoro Martinez had experienced 15 sulfuric acid spills in the five years preceding the 2014 incident. Each spill was a near-miss for a more serious injury. None were adequately investigated as systemic precursors.

Finding 2

Inadequately Tightened Compression Fitting Failed

A compression fitting at a sulfuric acid sampling station had been inadequately tightened during a recent maintenance activity. The fitting failed under operating pressure, releasing 84,000 lbs of concentrated sulfuric acid.

Finding 3

84,000 Lbs Concentrated Sulfuric Acid Released

The fitting failure released approximately 84,000 pounds of concentrated sulfuric acid, burning two workers who were in the vicinity of the release.

Finding 4

Compression Fittings on Acid Lines as Recurring Problem

Prior acid spills at Tesoro Martinez had involved compression fittings as a contributing factor. No systematic engineering review or fitting replacement program had been implemented in response.

Finding 5

Tesoro Initially Denied CSB Access to Incident Site

Tesoro initially refused to allow CSB investigators access to the incident site and evidence, obstructing the investigation. This action reflected safety culture concerns beyond the immediate technical failure.

Finding 6

Two Workers Burned by Concentrated Acid

Two workers suffered first and second degree burns from the sulfuric acid release. Concentrated sulfuric acid causes severe, deep tissue burns on contact with skin.

🔍 Root Causes

Failure to Learn from 15 Prior Acid Spills

The fundamental failure was treating 15 acid spills in five years as individual incidents rather than as a pattern requiring systemic investigation, engineering solutions, and management accountability.

Inadequate Mechanical Integrity for Acid Fittings

The compression fitting that failed had been inadequately tightened during maintenance. The MI program did not include adequate verification of fitting tightness or replacement of compression fittings in concentrated acid service.

Inadequate Near-Miss Investigation and Corrective Action

Prior acid spills involving compression fittings were not investigated as systemic near-misses. Corrective actions from prior events did not eliminate the fitting failure mechanism.

Safety Culture Deficiency — Investigation Obstruction

Tesoro initial refusal to allow CSB site access reflected a safety culture that prioritized controlling information over learning from incidents — a systemic management deficiency beyond the technical failure.

☑ CSB Recommendations

→ Tesoro

Conduct a comprehensive investigation into the root causes of all 15 sulfuric acid spills in the five years preceding the 2014 incident and implement systemic engineering and management corrective actions.

→ Tesoro

Implement an engineering review and replacement program for compression fittings in concentrated sulfuric acid service, replacing with fittings of demonstrated reliability in acid environments.

→ Tesoro

Implement a near-miss investigation program that specifically tracks and analyzes all acid spills and releases as precursor events requiring corrective action, with management accountability for closure.

→ California OSHA

Require facilities with repeated process safety incidents to submit corrective action programs for regulatory review and approval, with defined timelines and accountability for implementation.

→ CSB / OSHA

Address investigator site access obstruction in process safety enforcement, clarifying the legal obligations of covered facilities to provide investigator access.

💡 Lessons Learned

⚠ Fifteen acid spills in five years is not a series of individual accidents — it is a pattern of systemic failure that screams for engineering investigation and management accountability. Each spill that is not investigated is a wasted warning.

⚠ Near-miss events are the most valuable data an organization has for preventing serious injuries. A spill of concentrated sulfuric acid without a fatality is a near-miss. Fifteen of them without investigation is fifteen wasted opportunities.

⚠ Compression fittings in concentrated mineral acid service deserve engineering scrutiny. If compression fittings have been involved in multiple releases, engineering should evaluate whether they are appropriate for the service or should be replaced with a more reliable fitting type.

⚠ Safety culture is reflected in how organizations respond when their failures are investigated. Obstruction of an incident investigation is an indicator of a culture that has not accepted accountability for process safety performance.

⚠ Repeating acid spills and burns demonstrate that personal protective equipment alone is not adequate to protect workers from acid release hazards. Engineering controls — better fittings, proper maintenance procedures, and investigative follow-through — are required.

PSM Elements: MI · INC · SOP · HOW · EP

🔨 Safety Meeting Toolbox Talk

Topic: Acid Spill Prevention & Near-Miss Pattern Recognition

💬Does our facility track and investigate all acid spills and releases as near-miss events requiring root cause analysis and systemic corrective action — not just as routine maintenance cleanup items?

💬Have compression fittings, sampling connections, and other small-bore fittings in concentrated acid service been reviewed for fitness-for-purpose in the specific service conditions they are exposed to?

💬When the same type of failure has occurred multiple times at our facility, is there a defined process for escalating to a systemic root cause investigation rather than individual incident reports?

💬Are workers in acid handling areas equipped with adequate personal protective equipment, emergency eyewash and shower stations, and procedures for responding to acid contact?

💬Does our safety culture reflect a commitment to transparent incident reporting and investigation — including cooperation with regulatory and external investigators when incidents occur?

✎ Team Action Items

✓Pull all maintenance work orders and incident reports related to acid fittings and connections in the past three years — identify any patterns of recurring failure and confirm they have been investigated systemically

✓Review all compression fittings and small-bore connections in concentrated acid service in your area — verify they are the appropriate fitting type for the service and have been tightened per manufacturer specifications

✓Confirm that all acid spills and releases in your area — even minor ones cleaned up without injury — are reported and captured in the near-miss investigation system

✓Verify that emergency eyewash and safety shower stations are within 10 seconds travel of all acid handling areas and that they have been flushed and flow-tested within the past month

🔗 PSM Failures Behind This Incident

This incident traced to breakdowns across 5 PSM elements (MI · INC · SOP · HOW · EP). Each represents a documented gap that process safety documentation and consulting can close before a similar event occurs at your facility.

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.

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Incident Investigation

Near-misses and prior incidents almost always signal the exact failure mode that eventually becomes fatal. When investigation is absent or superficial, those warnings go unheeded until consequences arrive.

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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.

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Hot Work Permits

Unauthorized or poorly controlled ignition sources near flammable atmospheres are entirely preventable. A rigorous hot work permit system with pre-job atmospheric testing closes this pathway.

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Employee Participation

OSHA PSM requires workers to be meaningfully involved in hazard analyses and procedure development — not just trained on the finished product. Active participation catches gaps that management alone misses.

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