U.S. CHEMICAL SAFETY AND HAZARD INVESTIGATION BOARD

INVESTIGATION REPORT

REPORT NO. 2008-01-I-CO

AUGUST 2010

XCEL ENERGY HYDROELECTRIC PLANT

PENSTOCK FIRE

(Five Dead, Three Injured)

 

CABIN CREEK

GEORGETOWN,

COLORADO

OCTOBER 2, 2007

KEY ISSUES:

SAFE LIMITS FOR WORKING IN CONFINED 

SPACE FLAMMABLE ATMOSPHERES

PRE-JOB SAFETY PLANNING OF 

HAZARDOUS MAINTENANCE WORK

CONTRACTOR SELECTION AND 

OVERSIGHT

EMERGENCY RESPONSE AND RESCUE
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Table of Contents

1.0 EXECUTIVE SUMMARY ...........................................................................................................10

1.1 Incident Synopsis...........................................................................................................................10

1.2 Scope of the Investigation..............................................................................................................10

1.3 Incident Description.......................................................................................................................11

1.4 Increasing Need for Penstock Recoating .......................................................................................12

1.5 Key Findings..................................................................................................................................12

1.6 Recommendations..........................................................................................................................17

1.7 Conduct of the Investigation..........................................................................................................18

2.0 XCEL ENERGY............................................................................................................................21

2.1 Cabin Creek Hydroelectric Plant ...................................................................................................21

2.1.1 Penstock............................................................................................................................22

2.1.2 Deteriorated Penstock Interior Lining Requires Replacement..........................................24

3.0 CONTRACTORS ..........................................................................................................................26

3.1 RPI Coating, Inc. ...........................................................................................................................26

3.2 KTA-Tator, Inc. .............................................................................................................................26

4.0 INCIDENT DESCRIPTION..........................................................................................................27

4.1 Pre-Incident Events........................................................................................................................27

4.1.1 Initial Evaluations of the Penstock Project Hazards.........................................................27

4.1.2 Contractor Selection .........................................................................................................28

4.1.3 Planning and Preparing for Penstock Recoating Project ..................................................28

4.1.4 Work Preparation Prior to Recoating................................................................................29

4.1.5 Removal of Old Epoxy Liner............................................................................................31

4.1.6 Additional Evaluations and Inspections of the Penstock Work Space .............................32

4.1.7 Staging Equipment and Coating Materials.......................................................................33

4.1.8 Preparation for Coating Application.................................................................................38

4.1.9 Epoxy Coating Application Problems ..............................................................................39

4.2 The Incident ...................................................................................................................................41

4.3 Emergency Response .....................................................................................................................41

4.3.1 Fire Extinguishers.............................................................................................................41

4.3.2 Initial 9-1-1 Call................................................................................................................42

4.3.3 Emergency Responders Arrive .........................................................................................43
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4.3.4 Call for Mutual Aid...........................................................................................................44

4.3.5 Attempted Entry by Early Rescuers..................................................................................44

4.3.6 Stranded Workers Still Communicating 45 Minutes into Incident...................................45

4.3.7 Emergency Responders Evaluate Further Entry into the Penstock...................................45

4.3.8 Emergency Responders Enter the Penstock......................................................................45

5.0 INCIDENT ANALYSIS................................................................................................................46

5.1 Pre-Incident Events........................................................................................................................46

5.1.1 Insufficient Ventilation .....................................................................................................46

5.1.2 Improper Equipment Choices for Fire Prevention............................................................47

5.1.3 Scheduling and Production Pressures...............................................................................52

5.2 Incident Events ..............................................................................................................................54

5.2.1 Unsafe Sprayer Flushing Method Contributed to a Flammable Atmosphere ...................54

5.2.2 Most Probable Ignition Source .........................................................................................54

5.2.3 Flash Fire Becomes Sustained Toxic Fire, Trapping Workers.........................................57

6.0 CONFINED SPACE......................................................................................................................58

6.1 Penstock is a Permit-Required Confined Space.............................................................................58

6.1.1 Initial Evaluation of the Confined Space Indicated a Permit-Required Program was 

Necessary 59

6.1.2 The Known Work Activities in the Penstock Necessitated a Permit-Required Confined 

Space Program....................................................................................................................................60

6.1.3 Permit-Required Confined Space Inadequately Declassified ...........................................61

6.2 Lack of Pre-Job Safety Planning for Hazards................................................................................62

6.3 No Monitoring Plan Established....................................................................................................64

6.4 No Evaluation of Hazards When Conditions Changed..................................................................65

6.5 Safer Solvent Not Chosen..............................................................................................................66

6.5.1 The Hazards of MEK........................................................................................................66

6.5.2 Safer Alternatives .............................................................................................................70

6.6 Xcel‘s and RPI‘s Confined Space Policies....................................................................................70

7.0 EMERGENCY RESPONSE AND RESCUE................................................................................72

7.1 Lack of Preparation by Xcel and RPI to Ensure Availability of Qualified Rescue Personnel.......73

7.2 Failure by Xcel and RPI to Arrange for Timely Rescue................................................................74

7.2.1 Requirements and Recommendations for Alternate Escape Routes or Safety Chambers 76
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7.3 Lack of a Technical/Confined Space Rescue Certification Progarm for Volunteer Firefighters...78

8.0 CONTRACTOR SELECTION AND OVERSIGHT ....................................................................80

8.1 Contractor Selection.......................................................................................................................80

8.1.1 Contractor Selection Process for the Penstock Project Request for Proposal...................80

8.1.2 RPI Safety Record ―Not Acceptable,‖ but Allowed to Bid ..............................................82

8.1.3 Contractor Selection and Safety: Historical Background .................................................83

8.1.4 Contractor Selection and Safety: Current Industry Guidelines.........................................84

8.1.5 Xcel Corporate Policies on Contractor Selection .............................................................86

8.2 Contractor Oversight......................................................................................................................87

8.2.1 Safety Addendum Added to Contract...............................................................................87

8.2.2 Xcel Cabin Creek Site Contractor Oversight Activities and RPI Safety Performance .....88

8.2.3 Xcel Corporate Policies and Other Requirements Addressing Contractor Oversight ......90

9.0 EMPLOYEE SAFETY TRAINING..............................................................................................92

9.1 Company-Specific Safety Training................................................................................................93

9.2 Training Center Safety Training ....................................................................................................94

9.3 Generic Onsite Training Provided at Cabin Creek ........................................................................96

9.4 Safety Training Needs Specific to the Penstock ............................................................................98

9.4.1 Substituting Non-flammables for Flammable Solvents....................................................99

9.4.2 Safe Handling and Use of Flammables.............................................................................99

9.4.3 Flammable Atmospheres and Confined Space Entry .....................................................100

9.4.4 Fire Prevention and Mitigation .......................................................................................100

9.4.5 Proper and Safe Use of the Sprayer and Associated Equipment ....................................101

10.0 REGULATORY AND INDUSTRY STANDARDS ANALYSIS..............................................103

10.1 Hazards of Confined Space Work in Potentially Flammable Atmospheres Inadequately Covered 

in Existing Standards ................................................................................................................................103

10.2 Other Regulations and Safety Guidelines Set Protective LEL Limits for Work in Potentially 

Flammable Atmospheres ..........................................................................................................................106

10.3 Colorado Public Utilities Commission ........................................................................................108

11.0 FLAMMABLES USED IN CONFINED SPACES: OTHER INCIDENTS ...............................111

12.0 ROOT AND CONTRIBUTING CAUSES..................................................................................113

12.1 Root Causes .................................................................................................................................113

12.2 Contributing Causes.....................................................................................................................114
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13.0 RECOMMENDATIONS.............................................................................................................116

REFERENCES .........................................................................................................................................125

APPENDIX A: INCIDENT TIMELINE ..............................................................................................131

APPENDIX B: REGULATORY HISTORY OF RPI COATING, INC. ...........................................136

APPENDIX C: INVENTORY OF FLAMMABLE AND COMBUSTIBLE MATERIAL IN 

PENSTOCK.............................................................................................................................................146

APPENDIX D: EVALUATION OF IGNITION SOURCES..............................................................147

D.1 Static Ignition of Explosive MEK Vapor-Air Mixture inside Sprayer Base Hopper...................147

D.2 Stray Current Ignition of Explosive MEK Vapor-Air Mixture inside the Sprayer Base Hopper 153

D.3 Ignition of Explosive MEK Vapor-Air Mixture by Halogen Lights atop the Sprayer ................155

D.3.1 Ignition Caused by Halogen Lamps................................................................................157

D.4 Hot Surface Ignition by the Sprayer Heater(s).............................................................................161

D.5. Compression Ignition inside One of the Sprayer Piston Pumps..................................................161

D.6 Electrical Spark from Heater Control Box...................................................................................161

APPENDIX E: MEK FLAMMABILITY PROPERTIES AT PENSTOCK CONDITIONS ..........162

APPENDIX F: LOWEST MINIMUM IGNITION ENERGY AT PENSTOCK CONDITIONS ...166

APPENDIX G: WORK ACTIVITIES ALLOWED IN POTENTIALLY EXPLOSIVE 

ATMOSPHERES....................................................................................................................................168

APPENDIX H: APPLICABLE OSHA CONFINED SPACE STANDARDS....................................175

H.1 OSHA General Industry Standards (29 CFR 1910).....................................................................175

H.2 Electrical Power Generation (29 CFR 1910.269)........................................................................175

H.3 Permit-Required Confined Spaces (29 CFR 1910.146)...............................................................176

APPENDIX I: CSB CONFINED SPACE INCIDENTS DATA INCLUSION CRITERION AND 

LIMITATIONS.......................................................................................................................................177

APPENDIX J: SIMILAR RECENT CONFINED SPACE INCIDENTS INVOLVING 

FLAMMABLES INVESTIGATED BY THE CSB..............................................................................179

13.1.1 ConAgra Foods Processing Plant Explosion ..................................................................179

13.1.2 TEPPCO Terminal Explosion.........................................................................................179
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Figures

Figure 1. Location of hydroelectric plant, reservoirs, and penstock pathway ............................................22

Figure 2. Penstock configuration ................................................................................................................23

Figure 3. Upper reservoir mushroom access hatch .....................................................................................24

Figure 4. Access door cut into penstock for recoating work.......................................................................30

Figure 5. The epoxy sprayer system used within the penstock...................................................................34

Figure 6. The solvent pump on the back side of the epoxy sprayer............................................................35

Figure 7. Aerial view of equipment arrangement in work area of the penstock .........................................36

Figure 8. Depiction of contractors working with the sprayer immediately prior to the flash fire ..............37

Figure 9. Depiction of contractors recoating the penstock interior near the temporary west bulkhead......38

Figure 10. Remains of the halogen light sitting atop the sprayer inside the penstock (left); the same 

remains being compared to an exemplar halogen light (right). ..........................................................50

Figure 11. The winding, steep and narrow road from Georgetown to the Xcel hydroelectric plant...........76
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Acronyms and Abbreviations

AIHA American Industrial Hygiene Association

ANSI American National Standards Institute

API American Petroleum Institute

APPA American Public Power Association

ASTM American Society for Testing and Materials

ATSDR Agency for Toxic Substances and Disease Registry

ATV all-terrain vehicle

BLS Bureau of Labor Statistics

CBI Colorado Bureau of Investigation

CCC Certified Coatings Company

CCFA Clear Creek County Fire Authority

CDFS Colorado Division of Fire Safety

CFOI Census of Fatal Occupational Injuries 

CSB U.S. Chemical Safety and Hazard Investigation Board

CURT Construction Users Roundtable

EMR experience modification rate

EPA Enviornmental Protection Agency

EPRI Electric Power Research Institute

ESD Emergency Services District

FACE Fatality Assessment and Control Evaluation 

FERC Federal Energy Regulatory Commission

FSA Formal Settlement Agreement

HSEES Hazardous Substances Emergency Events Surveillance

IChemE Institution of Chemical Engineers

IDLH Immediately Dangerous to Life and Health

IIPP Injury and Illness Prevention Program

IMIS Integrated Management Information System

LEL Lower Explosivity Limit

LFL Lower Flammability Limit

MEK methyl ethyl ketone

MSDS Material Safety Data Sheet

MW megawatt
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NACE National Association of Corrosion Engineers

NFPA National Fire Protection Association

NIOSH National Institute of Occupational Safety and Health

OIICS Occupational Injury and Illness Classification 

OSHA Occupational Safety and Health Administration

PHA Process Hazard Analysis

PPE Personal Protective Equipment

ppm parts per million

PSCo Public Service Company of Colorado

psig pounds per square inch gauge

PSCo Public Service Company of Colorado

PSM Process Safety Management

PUC Colorado Public Utilities Commission

QP 1 Qualification Procedure No. 1

RFP Request for Proposal

SCBA Self Contained Breathing Apparatus

SCPDI Southern California Painting and Drywall Industries 

SSPC Society of Protective Coatings (formally Steel Structures Painting Council)

TRB Transportation Research Board of the National Academies
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1.0 Executive Summary

1.1 Incident Synopsis

On October 2, 2007, a chemical fire inside a permit-required confined space1at Xcel Energy‘s 

hydroelectric plant in a remote mountain location 45 miles (72 kilometers) west of Denver, Colorado, 

killed five and injured three workers. Industrial painting contractors were in the initial stages of recoating

the 1,530-foot (466-meter) steel portion of a 4,300-foot (1,311-meter) enclosed penstock2tunnel with an 

epoxy coating product when a flash fire occurred. Flammable solvent being used to clean the epoxy 

application equipment in the open penstock atmosphere ignited, likely from a static spark. The initial fire 

quickly grew as it ignited additional buckets of solvent and substantial amounts of combustible epoxy 

material, trapping and preventing five of the 11 workers from exiting the single point of egress within the 

penstock. Fourteen community emergency response teams responded to the incident. The five trapped 

workers communicated using handheld radios with co-workers and emergency responders for 

approximately 45 minutes before succumbing to smoke inhalation.

1.2 Scope of the Investigation

Catastrophic workplace accidents typically are not the result of a single error or one piece of faulty 

equipment; rather, higher-level safety system deficiencies are often found at facilities where such 

accidents occur. It has also been established that accident prevention is most effective when these 

 

1 The US Occupational Safety and Health Administration (OSHA) defines, in its general industry rule, a confined 

space as having three attributes: (1) large enough to enter and perform work; (2) limited access and egress; and (3) 

not designed for continuous occupancy. OSHA states that a permit-required confined space has one or more of the 

following characteristics: ―(1) contains or has the potential to contain a hazardous atmosphere; (2) contains 

material that has the potential for engulfing an entrant; (3) has an internal configuration such that an entrant could 

be trapped or asphyxiated by inwardly converging walls or by a floor that slopes downward and tapers to a smaller 

cross section; or (4) contains any other recognized serious safety or health hazard. OSHA has identified one type 

of hazardous atmosphere as  ̳[f]lammable gas, vapor or mist in excess of 10% of its lower flammable limit (LFL)‘ 

[29 CFR 1910.146(b)].

2 A penstock in hydroelectric service is typically an enclosed conduit such as a tunnel or pipe that delivers a flow of 

water to a turbine that generates electric power
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systemic causes are understood and learned.3 As such, the U.S. Chemical Safety Board (CSB) examined 

both the technical and organizational causes of the fire at Xcel Energy‘s Cabin Creek penstock. 

The investigation found that a number of safety issues contributed to the accident, including a lack of 

planning for hazardous work, inadequate contractor selection and oversight, and insufficient regulatory 

standards pertaining to the use of flammables within confined spaces. The investigation also examined the 

technical aspects of recoating a penstock, the work conditions of the unique confined space, and the 

training the contractors received prior to starting work. Finally, the CSB evaluated aspects of emergency 

response, including planning for timely and qualified rescue and the need for certified confined space 

rescue responders in the state of Colorado.

1.3 Incident Description

On October 2, 2007, a work crew of industrial painters employed by RPI Coating, Inc. (RPI) began 

applying a new epoxy coating to the steel interior section of the penstock4at the Cabin Creek 

hydroelectric plant operated by Xcel Energy, Inc. (Xcel), located south of Georgetown, Colorado. 

Shortly after the epoxy application commenced, the work crew experienced problems with the spraying 

process, resulting in poor coating quality. Spraying was terminated and the crew began cleaning the 

sprayer system equipment with a flammable solvent, methyl ethyl ketone (MEK),5to remove epoxy

residue before taking the equipment out of the penstock. During this cleaning operation, MEK vapors 

 

3 The Center for Chemical Process Safety (CCPS) states that identifying the underlying or root causes of an incident 

has a greater preventative impact by addressing safety system deficiencies and averting the occurrence of 

numerous other similar incidents, while addressing the immediate cause only prevents the identical accident from 

recurring (1992). 

4 The Cabin Creek penstock is a tunnel with a diameter that varies between 12 and 14 feet that runs between two 

reservoirs; water flows from the upper reservoir to the lower reservoir through the penstock, passing over turbines 

which produce electricity (see Section 2.1.1.1).

5 Methyl ethyl ketone (MEK) is an organic chemical compound often used as a solvent in painting activities listed 

by the National Institute for Safety and Health (NIOSH) as ―highly flammable.‖ NIOSH MEK International 

Chemical Safety Cards, 1998. MEK is a Class IB flammable liquid, with a flash point below 73°F (23°C) and 

boiling point at or above 100°F (38°C). NIOSH Pocket Guide to Chemical Hazards, 2005
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inside one of the two epoxy hoppers ignited and flashed. The resulting fire grew quickly, consuming 

several other open containers of MEK and numerous buckets of epoxy material positioned around the 

sprayer. 

Four RPI crew members positioned on the side of the fire nearest the exit evacuated the penstock, 

although three were later treated for injuries: one received minor burns, one fractured his arm, and another 

suffered breathing difficulties. Five additional crew members trapped opposite the exit were unable to 

evacuate due to the fire and narrow configuration of the penstock. The five workers later succumbed to 

smoke inhalation inside the penstock and died.

1.4 Increasing Need for Penstock Recoating

Many hydroelectric plants have steel penstocks that have not been relined or recoated for many years. In 

North America, estimates suggest that 3 million feet (1 million meters) of in-service penstocks exist. 

Interior coatings and linings are required to maintain the structural integrity and serviceability of 

penstocks to prevent corrosion and provide water tightness. When periodic internal inspections uncover 

linings that have deteriorated to the extent that rehabilitation is no longer possible, repair projects are 

initiated to remove the old penstock linings and replace them with newer epoxy coatings that typically 

have a 20- to 30-year service life (EPRI, 2000, ch. 1-3). Removing the old linings and applying new 

interior coatings in penstocks present special hazards to workers, including potential flammable and/or 

toxic atmospheres and limited access and egress within these confined spaces.

Because of the serious nature of this incident and the unique hazards associated with penstock coating 

work, the CSB launched an investigation to determine root and contributing causes and to make

recommendations to help prevent similar incidents.

1.5 Key Findings

1. On the day of the incident, approximately 16 gallons (61 liters) of highly flammable methyl ethyl 

ketone (MEK) solvent stored in plastic buckets was used in the penstock to clean the epoxy 
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sprayer and associated equipment. The cleaning involved pouring MEK into the sprayer‘s two 

hoppers and circulating it through the sprayer in the open penstock atmosphere. A number of 

ignition sources present or created by the work activity were not eliminated or controlled. The 

circulation of MEK through non-conductive hose likely led to static discharge, igniting the MEK 

in the sprayer hopper and resulting in a flash fire.

2. Xcel and RPI managers were aware of the plan to operate the epoxy sprayer inside the penstock 

and the need to use solvent to clean the sprayer and associated equipment in the open penstock 

atmosphere during the epoxy application portion of the project. However, they did not perform a 

hazard evaluation of the epoxy recoating work; as a result, they failed to identify serious safety 

hazards involving use of flammable liquids within the confined space. Effective controls were not 

evaluated or implemented during their pre-job safety planning, such as substituting MEK with a 

non-flammable solvent. 

3. During the recoating project, neither Xcel nor RPI treated the Cabin Creek penstock as a permitrequired confined space, nor did they re-evaluate hazards in the space caused by changing work 

activities. Such activities included the introduction of flammables into the penstock, hot work

within the confined space, and the switch from abrasive blasting to recoating of the penstock 

interior.

4. Neither Xcel‘s nor RPI‘s corporate confined space programs adequately addressed the special 

precautions necessary to safely manage the hazard of potential flammable atmospheres. Their 

policies and procedures did not address the need for a confined space monitoring plan or the need 

for continuous monitoring in the work area where flammables were being used. Neither of their

permit-required confined space policies or permit forms required or established a maximum 
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permissible percentage of the lower explosive limit (LEL)6for safe entry and occupancy inside a 

permit space.

5. On the day of the incident, RPI monitored the atmosphere of the penstock, a permit-required 

confined space, for flammable atmospheres only at is entrance, 1,450 feet (442 meters) from the 

work activities, rather than where flammables were being used. 

6. The majority of RPI employees working at Cabin Creek had not received comprehensive formal 

safety training; effective training on company policies; or site-specific instruction addressing 

confined space safety, the safe handling of flammable liquids, the hazard of static discharge, 

emergency response and rescue, and fire prevention. The Joint Apprenticeship Training 

Committee and Center, established by the parties to the Painters and Allied Trades District 

Council 36 Master Labor Agreement (including RPI), provide comprehensive safety training on 

these topics as part of its apprenticeship program, but most of the painters hired by RPI had not 

taken these courses nor had they otherwise received documented equivalent safety training.

7. The U.S. Occupational Safety and Health Administration‘s (OSHA) Permit-Required Confined 

Spaces Rule for general industry establishes no maximum permissible percentage of the LEL for 

safe entry and occupancy inside a permit space. OSHA has interpreted its rule to allow working 

in a permit-required space where the atmosphere is above 10 percent of the LEL.7 However, the 

rule defines a flammable concentration above 10 percent of the LEL as a hazardous atmosphere 

―that may expose employees to the risk of death, incapacitation, impairment of ability to self-

 

6

 LEL is defined as ―that concentration of combustible material in air below which ignition will not occur‖ in 

Recommended Practice for Handling Releases of Flammable and Combustible Liquids and Gases, NFPA 329 

(2005). The terms LEL and lower flammability limit (LFL) have different definitions but are commonly used 

interchangeably. This report uses LEL except where citing other sources that use LFL in their standard or 

regulation. The OSHA Permit-Required Confined Space Standard 29 CFR 1910.146 uses the term LFL in its 

provisions.

7 Letter to Macon Jones, Blasting Cleaning Products LTD, from John B. Miles Jr., Director, dated September 4, 

1996, concerning entry into a confined space when the LFL is greater than 10 percent.
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rescue...injury, or acute illness‖ [29CFR 1910.146(b)]. Other OSHA regulations addressing 

confined and enclosed spaces in the maritime industry and other sectors prohibit entry and work 

activities above a specific percentage of the LEL (such as 10 percent). The recent trend of 

consensus safety guidance and regulatory requirements from other jurisdictions has been to 

establish safe work limits for confined space flammable atmospheres substantially below the 

LEL.

8. The CSB identified identified 53 serious flammable atmosphere confined space incidents 

involving fires and explosions from 1993 to April 2010; 57 percent involved a fatality. These 

incidents caused 54 injuries and 45 fatalities, a majority of which occurred since 2003. These 

flammable atmosphere incidents include two the CSB investigated in 2009 where confined space 

explosions resulted in four fatalities.

9. The penstock had only one egress point. Published safety guidance for penstocks discusses the 

importance of alternative escape routes in the event of an emergency (ASCE, 1998, pp. 2-8). Xcel 

Energy had identified the sole egress point as a major concern in the penstock planning as had 

RPI personnel; however, no remedial action was taken. When the flash fire occurred, five RPI 

workers who were on the side of the sprayer opposite the exit became trapped by the growing fire 

and restricted egress. 

10. The planned use of flammable solvent in the open atmosphere inside the penstock created the 

potential for an immediately dangerous to life or health (IDLH)

8

flammable atmosphere. Xcel‘s

and RPI‘s emergency response plan for rescue services for the penstock reline project was to call 

 

8

IDLH, or Immediately Dangerous to Life or Health, is a personal exposure limit for a chemical substance set forth 

by the National Institute of Occupational Safety and Health (NIOSH); it is typically expressed in parts per million 

(ppm). OSHA‘s Permit-Required Confined Spaces rule for general industry states that IDLH ―means any condition 

that poses an immediate or delayed threat to life or that would cause irreversible adverse health effects or that 

would interfere with an individuals ability to escape unaided from a permit space‖ [29 CFR 1910.146(b)]. 
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9-1-1 emergency dispatch. No emergency responders with confined space technical rescue 

certification were at the hydroelectric plant and immediately available for rescue on the day of the 

incident, and the approximate response time of the closest identified certified community rescue 

service was approximately 1 hour and 15 minutes. The trapped workers died from smoke 

inhalation approximately 1 hour before this response service arrived on site.

11. While the Colorado Division of Fire Safety (CDFS) does not track technical rescue certification 

in the state, available evidence indicates a limited number of Colorado emergency response 

organizations with personnel certified individually by an accredited program in technical rescue. 

The CDFS has a voluntary accredited certification program for firefighters and hazardous 

materials responders but does not offer certification for technical rescue, including confined space 

rescue. 

12. Xcel‘s prequalification process9for determining which potential contractors were allowed to 

participate in the Cabin Creek bid process considered only the contractors‘ financial capacity and 

did not disqualify bidders based on unacceptable past safety performance. 

13. Once prequalified, Xcel reviewed and ranked the contractors‘ proposals, considering factors such 

as past performance, quality, and safety records in addition to price. RPI received the lowest 

score, ―zero,‖ in the safety category, which, according to Xcel‘s evaluation form, meant that the 

proposal should have been automatically rejected. However, RPI was still allowed to compete for 

the contract. While another contractor‘s proposal was judged the best from a technical and quality 

perspective, RPI‘s proposal received the highest ranking in the evaluation process, based 

primarily on low price.

 

9 When contractors are selected, an initial prequalification process is often used during which each potential 

contractor must meet basic qualifications. In this case, Xcel‘s prequalification process considered only the 

financial capacity of the potential contractor.
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14. Due to concerns about RPI‘s record of injuries and fatalities in past projects, Xcel added a safety

addendum to the penstock recoating contract affirming that Xcel would ―closely observe‖ RPI‘s 

safety performance during the recoating project. During the initial penstock project activities 

prior to the incident, Xcel managers became aware of several significant safety problems 

attributable to RPI, including a recordable injury where an RPI worker was sent to the hospital; 

the evacuation of the penstock due to high readings of carbon monoxide, a toxic gas; and 

electrical problems that resulted in the destruction of penstock equipment. These problems did not 

result in Xcel increasing its scrutiny of RPI‘s safety performance or taking corrective action.

15. Prior to the incident, Xcel corporate officials had not conducted safety audits examining company 

adherence to its corporate policies on contractor selection and oversight at each of its powergenerating facilities. 

1.6 Recommendations

As a result of this investigation, the CSB makes recommendations to the following recipients:

U.S. Occupational Safety and Health Administration (OSHA)

Governor of Colorado 

Colorado Public Utilities Commission

Director of the Colorado Division of Fire Safety

Director of the Colorado Division of Emergency Management 

Xcel Energy

RPI Coating

American Public Power Association

Society for Protective Coatings 
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Southern California Painting and Drywall Industries Joint Apprenticeship and Training 

Committee

Section 13.0 of this report provides the detailed recommendations.

1.7 Conduct of the Investigation

The CSB investigation team arrived at the incident scene on October 3, 2007, the day after the incident. 

They joined the Incident Command structure and began on-scene investigation activities. That same day, 

Incident Command demobilized, and emergency responders disbanded after the five deceased RPI crew 

members were removed from the penstock. Investigative teams from the Colorado Bureau of 

Investigation (CBI), OSHA, and the CSB remained onsite and worked with Xcel management to protect 

and preserve evidence at the Cabin Creek site within the penstock, as well as those areas of the Cabin 

Creek site relevant to the case, including the upper reservoir.

After careful and extensive pre-entry safety planning with all involved parties, the CSB entered the 

penstock on two separate occasions (November 6 and 11, 2007) to examine the incident scene, and was 

present onsite when evidence was removed from the penstock on December 19, 2007. Investigators 

video-and photo-documented evidence, took numerous size and distance measurements, and physically 

examined all items within the penstock. Through joint agreements with all involved parties, the 

equipment and associated evidence within the penstock were removed to a secure site; the evidence was 

more thoroughly examined on two separate occasions: December 12, 2007, and January 7, 2009. 

The team conducted more than 54 interviews throughout the course of its investigation, collecting the 

testimony of employees from the various companies involved in the penstock project, emergency 

responders, officials from the sprayer system manufacturer, supervisors from other contractors involved 

in penstock recoating work, Colorado state officials, and union training center representatives. The CSB 

examined a variety of company documents, including those pertaining to contractor selection and 

management, safety policies and practices, and employee training, as well as the contractual agreements
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19

between Xcel and the various contractors involved in the penstock project. Samples of material taken 

from burned buckets and the sprayer hoppers were also tested in a laboratory for identification and 

composition analysis. This investigative work activity was coordinated with OSHA, the CBI, and the 

various companies involved in the penstock coating project. 

The CSB encountered a number of obstacles and lack of cooperation in regard to the involved parties of

the investigation, including Xcel and RPI. Xcel failed to fully respond to a number of CSB requests for 

both records and interrogatories. The CSB required the assistance of the U.S. Attorney‘s Office for the 

District of Colorado, Civil Division, to attempt to obtain information relevant to its investigation from 

Xcel. RPI did not respond to numerous interrogatory requests and a number of RPI managers asserted 

their constitutional right against self incrimination. 

Near the end of the CSB‘s investigation in the spring of 2010, Xcel and RPI who faced criminal charges 

arising from the Cabin Creek fatalities took the unprecedented step of going to federal court to block the 

publication of the CSB report.10 Ultimately, the presiding judge squarely rejected Xcel‘s effort to prohibit 

publication of the CSB‘s findings and recommendations:

Based on the evidence presented at the June 24, 2010 hearing, the arguments, and the applicable 

law, I find Defendants‘ arguments to be without merit. Moreover, the Defendants cite no 

authority in support of their request that I bar the issuance of the CSB‘s final Cabin Creek report. 

First, I find the CSB acted as an independent federal agency in conducting its investigation and 

drafting its report as required by 42 U.S.C. §7412(r)(6)(A)-(S). There is no evidence whatsoever 

that the CSB acted in concert with the prosecution in investigating this accident or intentionally 

delayed the issuance of its report.11

While CSB‘s position was supported by a federal district judge, Xcel and RPI‘s legal action delayed 

completion of the CSB report for several months, and diverted CSB resources from other ongoing 

 

10 United States v. Xcel Energy, Inc., et al., No. 09-cr-00389-WYD (District of Colorado).

11 Id. Order of June 30, 2010 (docket #178).
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investigations. Despite the clear findings to the contrary in the judge‘s ruling, Xcel representatives 

continued to make unsupported claims that the CSB had delayed release of its report to prejudice Xcel in 

the federal criminal prosecution in which the company is a defendant. 

Finally, in early August 2010, an Xcel attorney provided an incomplete draft of the CSB report to the 

media on the eve of the Board‘s completion of its work. This last Xcel effort caused yet further delays in 

the process, and has created a risk that Xcel‘s Directors and shareholders will draw incorrect conclusions 

about the accident at Cabin Creek. Accordingly, the Board included in this report a formal 

recommendation that Xcel shareholders be directly notified by management of the significant findings 

and recommendations of this report, and of the actions Xcel management intends to take to implement 

needed safety improvements.
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2.0 Xcel Energy

Xcel Energy (Xcel) is a Minneapolis, Minnesota-based holding company founded in 1909 with four 

wholly owned regulated utility subsidiaries that serve electric and natural gas customers in eight western 

and Midwestern states: Colorado, Michigan, Minnesota, New Mexico, North Dakota, South Dakota, 

Texas, and Wisconsin. The company employs nearly 12,000; serves 3.3 million electricity and 1.8 million 

natural gas customers; and exceeds $9 billion in revenues annually (2008).

2.1 Cabin Creek Hydroelectric Plant

The Public Service Company of Colorado12 (PSCo) Cabin Creek hydroelectric plant, which began 

operating in 1967, is located off Guanella Pass, a partially paved road that winds through a remote area in 

the Rocky Mountains [10,018-foot (3053 meters) elevation] approximately 6 miles (10 kilometers) south 

of the Georgetown, Colorado and 45 miles (72 kilometers) west of Denver. PSCo is a subsidiary of Xcel; 

this report will refer to PSCo and Xcel Energy collectively as Xcel.

Cabin Creek is a pumped storage plant, with upper and lower water reservoirs totaling 1,977 acre-feet

(2439 megaliters), used to generate electricity primarily during peak demand periods. Electricity is 

generated by releasing water from the upper reservoir where it flows into an intake structure, which is 

connected to a penstock; the water passes through turbines before being deposited in the lower reservoir

(Figure 1). The flowing water rotates the turbines, which turn shafts that power the generators, producing

electricity. When electricity use is low, the water is pumped back into the upper reservoir through the 

penstock to be used again. The plant has two generators capable of producing 150 megawatts (MW) of 

electricity for 4 hours.

 

12 The Public Service Company of Colorado, a Denver-based company founded in 1869, is a regulated utility 

company in Colorado that operates seven coal, six hydroelectric, and two natural gas plants, and one wind turbine 

field, to provide electricity and natural gas utility services to 1.3 million customers located in Denver, other 

Colorado cities, and some rural areas.
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Figure 1. Location of hydroelectric plant, reservoirs, and penstock pathway

2.1.1 Penstock

The penstock is 4,163 feet (1,269 meters) long from the upper reservoir‘s intake to the point at which the 

penstock splits into two pipes to feed the turbines in the powerhouse. Of this space, 3,123 feet (952

meters) can be traveled by foot. RPI was hired by Xcel to recoat roughly one-half of this relatively 

horizontal space (1,560 feet, or 475 meters, at a 2 degree incline). This section of the penstock is 12 feet 

(3.7 meters) in diameter, welded and steel-lined. The remaining portions of the penstock going up into the 

mountain vary in length and degree of gradient, with the 55 degree section too steep to traverse (Figure 

2). The last 1,040 feet (317 meters) of the penstock requires climbing aids, ropes, or ladder structures to 

be traversed.
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Figure 2. Penstock configuration

At the highest elevation point of the penstock in the upper reservoir is the intake structure known as the 

―mushroom.‖ The mushroom is a 40-foot (12 meter) tall, cylindrical concrete and steel tower with 

screened openings near the top that open to the penstock. The mushroom has an access hatch 

approximately 20 feet (6.1 meters) above grade at a reverse incline position that requires climbing skill 

and significant physical strength to enter (Figure 3).
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Figure 3. Upper reservoir mushroom access hatch

While the penstock runs underground for most of its length, as it exits the mountain rock face near the 

lower reservoir, a 15-foot (4.6 meter) section is accessible from the powerhouse yard. In this portion of 

the penstock, a 4 by 6 foot (1.2 by 1.8 meter) opening was flame-cut into the steel penstock pipe to 

provide access for the recoating project workers and equipment. 

2.1.2 Deteriorated Penstock Interior Lining Requires Replacement

During the fall 2000 plant outage,13 a Federal Energy Regulatory Commission14 (FERC)-mandated 

internal inspection of the penstock found numerous indications of deterioration of the epoxy coating 

(flaking, blistering, and checking) in the interior of the steel-lined pipe section, which resulted in areas of 

 

13 An outage is a period when a plant, such as this one, is not in normal operation because of maintenance work 

and/or inspections.

14 FERC is a self-funded, independent regulatory agency within the U.S. Department of Energy with jurisdiction 

over electricity sales, wholesale electric rates, hydroelectric licensing, natural gas pricing, and oil pipeline rates. 

FERC also reviews and authorizes liquefied natural gas (LNG) terminals, interstate natural gas pipelines, and 

approximately 1,600 non-federal hydropower projects in the U.S. 
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25

rusting and pitting corrosion to the steel pipe. Although the structural integrity of the pipe had not been 

compromised, the inspection report recommended repairs to the coating before more damage resulted.

After obtaining an extension for repairs from FERC for several years, a project to remove the lining and 

replace it with a new epoxy lining was scheduled for the fall 2007 outage.
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3.0 Contractors

3.1 RPI Coating, Inc.

Xcel selected RPI Coating, Inc. (RPI), a commercial painting and coating company headquartered in 

Santa Fe Springs, California, to remove the old liner from the steel portions of the Cabin Creek penstock 

and apply the new epoxy (for additional information on the selection process, see Sections 4.1.2 and 8.0).

RPI, which operated as Robison-Prezioso, Inc. until 2007, was ranked the nation's seventh-largest 

specialty paint company based on revenues in 2005, according to the Engineering News-Record (2005).

At the time of the incident, RPI had approximately 275 employees and more than 13.5 million in annual 

sales.

Prior to this incident, when RPI was still Robison-Prezioso, federal and state OSHA had inspected the 

company 46 times since 1972. Of these inspections, 31 had been initiated due to a complaint, referral, or 

accident; 90 violations were issued with fines totaling $135,569. Some violations were issued after

accidents that had resulted in serious injuries and/or fatalities to employees (Appendix B). 

3.2 KTA-Tator, Inc.

Xcel hired KTA-Tator, Inc. (KTA), a 250-employee consulting/engineering firm, for several work tasks 

associated with the penstock project. These tasks included writing the technical specifications for the 

application of the new epoxy coating in the penstock, assisting in the selection of the coatings contractor 

by reviewing and evaluating submitted bids, helping resolve technical issues arising from application of 

the coating, and performing periodic quality control checks to ensure proper old coating removal and new 

coating application.

15

 

15 The first three tasks were completed by a KTA chemical engineer specializing in coatings applications in the 

water and power industries; the fourth was performed by a KTA coatings inspector certified by the National 

Association of Corrosion Engineers (NACE).
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4.0 Incident Description

The penstock fire occurred on October 2, 2007, but the recoating project had been initiated months 

earlier. 

4.1 Pre-Incident Events

4.1.1 Initial Evaluations of the Penstock Project Hazards

Almost a year before the October 2, 2007, incident, Xcel conducted a hazard assessment of the penstock 

project, which was later provided to potential contractors during the bidding process. However, this 

―Safety and Health Hazard Assessment Survey‖ focused only on the abrasive blasting portion of the 

recoat project work and did not examine the risks of epoxy recoating associated with the penstock, the use 

of flammables inside the confined space, or the limited access and egress of the penstock. This was the 

only hazard assessment Xcel conducted for the entire penstock recoating project.

Later in the penstock project development process, during the spring of 2007, a civil engineer employed 

by Xcel highlighted a number of difficulties specific to the unique and challenging penstock work that 

would affect the success of the project in his document, ―Cabin Creek Penstock Major Items of Concern.‖ 

Within the document, the civil engineer identified the need for an additional point of access, as the 

penstock‘s single entryway – a 20-inch (51 centimeters) man hole – was the only existing penstock 

opening at the start of the project. The civil engineer also discussed the challenges of trying to achieve the 

necessary temperature conditions within the penstock for successful epoxy application and the significant 

difficulties of completing the project in the 10 weeks allotted, suggesting that the harsh weather 

conditions typical of October and November in the Colorado mountains would hinder timely completion.

These concerns were given to the Xcel Cabin Creek principal engineer, who later became responsible for 

preparing for the project with RPI, and a number of other Xcel employees, prior to the start of the 

recoating work. Yet neither Xcel‘s submission to the potential bidders for the recoat project, nor RPI‘s bid 

response, discussed methods for minimizing or rectifying the concerns raised by the civil engineer. 
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4.1.2 Contractor Selection

Xcel issued a Request for Proposal (RFP) for a competitive bidding process to several contractors in July 

2007. The contractor selected to perform the work was to be chosen based upon the ―best value/best 

overall evaluated offer,‖ which was supposed to consider factors such as schedule, price, qualifications,

and safety performance (TRB, 2006, p.S-3). The Xcel process also included an initial prequalification 

step that examined the contractors‘ financial capacity to carry out the work but did not consider safety 

performance.

Due to key safety criteria deficits in RPI‘s safety record, Xcel rated the company as ―zero‖ in that 

category, which should have meant its automatic disqualification from the bidding process; however. 

RPI‘s bid was not rejected, and it was eventually awarded the contract despite its poor safety record 

(Section 8.0). 

4.1.3 Planning and Preparing for Penstock Recoating Project

While RPI employees prepped the job site, Xcel held a preconstruction meeting for the penstock recoating 

project on September 5, 2007, attended by an RPI vice president, the RPI Safety and Quality Control 

representative, and two RPI project foremen. During this meeting, the Xcel project manager indicated that 

this was a ―high profile project with [the] attention of FERC‖ and that a high standard toward quality 

control needed to be maintained. On September 10, at the request of RPI‘s safety director, an instructor 

with the Southern California Painting and Drywall Industries (SCPDI) District 36 Training Center 

conducted a six-hour safety refresher training session at the Xcel Cabin Creek site for some RPI industrial 

painters to address gaps that the Xcel safety director had identified in RPI‘s contract bid submissions. 

Only nine of the 14 RPI crew members were on site to attend this general safety training, and no make-up 

session was offered to those not in attendance (Section 9.0).
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4.1.4 Work Preparation Prior to Recoating 

Before the old liner could be removed from the steel sections and the new epoxy applied, the plant was

shut down and water drained from the penstock. This occurred during the first week of September 2007, 

as a number of RPI personnel began arriving at the Cabin Creek site to set up for the job. 

After the water was drained from the penstock, a 4-foot wide by 6-foot (1.2 by 1.8 meters) tall access 

opening was flame-cut16 into the side of the steel penstock pipe for personnel and equipment access. 

Wooden stairs and a ladder at the access door provided means for personnel to enter and exit the penstock

(Figure 4). 

Xcel and RPI personnel then entered the penstock to remove standing water, dead fish, mud, and debris. 

Eyewitnesses reported that the penstock was extremely slippery due to moss buildup, and that personnel 

often slipped during initial entries. One RPI employee dislocated his shoulder when he slipped and fell. 

 

16 The access opening was cut by a specialty welding contractor.
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Figure 4. Access door cut into penstock for recoating work

To contain the sandblasting debris and control ventilation, RPI built a wooden bulkhead west of the 

penstock area to be recoated (―west bulkhead‖), with a 2 by 2 foot (0.7 by 0.7 meter) access hatch near 

the bottom, and sealed it against the walls of the penstock with foam. RPI built a second sealed wooden 

bulkhead about 20 feet east of the penstock‘s access door (―east bulkhead‖). Two 20-inch (51 

centimeters) diameter flexible ventilation ducts, connected to dehumidification, heating, and dust 

collection equipment located outside the penstock, were brought into the penstock to dry and dehumidify 

the air and collect dust. The air supply duct was routed along the penstock wall and terminated near the 

west bulkhead at the steel/concrete transition where the air was discharged; the air return duct terminated 

near the penstock access door.

Compressed air and 120/240-volt electrical service were brought into the penstock to power equipment 

and provide lighting. Power cables for the electrical service were connected to a portable transformer 
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located outside the penstock. A 240-volt heavy gauge power cable (6 AWG17) ran along the penstock 

floor from the access door and terminated at power distribution centers (commonly called ―spider 

boxes‖), one of which was located about 100 feet (30.5 meters) from the west bulkhead to provide power 

to the work area; this cable had non-watertight twist lock connector fittings joining sections of cable. The 

spider box contained 240- and 120-volt GFCI-protected electrical power supply outlets. On the day of the 

incident, the electric heaters on the sprayer, halogen work lights positioned on top of the sprayer, and 

explosion-proof lighting mounted on a scaffold immediately adjacent to the bulkhead were plugged into 

this spider box.

On September 16, 2007, another contractor performing inspection work inside the penstock complained 

to Xcel about being delayed entry into the penstock for 2 hours due to high carbon monoxide (CO) levels; 

he also noted a problem with RPI‘s electrical service inside the penstock when some of the contractor‘s 

testing equipment was damaged after it was plugged into an RPI spider box. An RPI foreman later 

rewired this electrical box, which was located near the sprayer on the day of the incident. 

4.1.5 Removal of Old Epoxy Liner

Beginning on September 20, 2007, RPI sandblasted and removed the old liner from the the steel section

immediately east of the west bulkhead; sandblasting continued until September 28, when the first 500-

foot section was completed. On September 22, the Xcel project manager for the penstock recoating work 

observed RPI conducting abrasive blasting inside the penstock, noting that ―[w]ork conditions inside the 

penstock are highly hazardous on many levels. In the best of conditions, the coating removal is dirty, 

nasty work.‖ Beginning September 28 and continuing for 4 days, leaks were patched, and the abrasive 

 

17 AWG (American Wire Gauge) is a U.S. standard set of non-ferrous wire conductor sizes.
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blasting medium was vacuumed up and removed from the penstock. An Xcel worker entered the penstock 

during this period on two occasions to weld weep holes to stop leaks.

18

4.1.6 Additional Evaluations and Inspections of the Penstock Work Space

On September 22, KTA conducted its own initial pre-job hazard assessment of the penstock. In this 

assessment, the KTA inspector noted that the Material Safety Data Sheets (MSDSs) for all coatings and 

solvents to be used in the project were available and would be reviewed relative to personal protective 

equipment (PPE) and respiratory protection needs, and that the contractor and Xcel project manager were 

told about this review. In the assessment, the use of solvents was once again identified when the need for 

eye protection was pinpointed due to the use of ―solvents, paints, abrasives, etc.‖ According to the 

assessment document, the project manager was to be advised on the use of solvent.

In this same inspection, the KTA inspector also indicated that the project would require workers to enter a 

work area classified as a permit-required confined space. By delineating the space as such, several 

requirements were outlined to be followed, including review entry procedures and entry permit, verify 

that air monitoring is performed prior to and during entry, verify that an attendant is present and rescue 

equipment is onsite, and use respiratory protection in accordance with controlling employer‘s entry 

procedures. Despite these requirements, entry procedures were not developed and the required daily 

permits were incomplete and lacking detail pertaining to the hazards of the day‘s work activities. Air 

monitoring was performed almost exclusively at the entrance, about 1,450 feet (442 meters) away from 

the actual work area within the penstock. Finally, rescue equipment was not available and ready for use 

onsite throughout the project or on the day of the incident.

Two days later, on September 26, the KTA inspector conducted an inspection of the penstock interior, 

indicating in his documentation that thinner would be used as part of the coating materials‘ mixing and 

 

18 Neither Xcel Energy nor RPI could provide copies of hot work permits for this welding work to the CSB. 
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pre-application process. Thinner/solvent was required to be run through the sprayer system equipment 

(including hoses, nozzles, and the sprayer itself) prior to the introduction of the epoxy components. This

step ensured that the machine was completely free of all residue or contaminants prior to usage for actual 

spraying.19

On October 1, an Xcel safety consultant inspected RPI employees working in the penstock, but noted no

unsatisfactory conditions.

Sandblasting activities, including hand-sanding and grinding of the walls, were completed on the morning 

of October 2, and 13 RPI crew members20 began preparing the penstock interior for the new coating. No 

reevaluation of the safety hazards was held that morning to specifically assess new risks that could be 

associated with the change in planned work activities from sandblasting to epoxy coating application, nor 

were special precautions taken within the work environment beyond those put in place prior to the start of 

the sandblasting operation. 

4.1.7 Staging Equipment and Coating Materials

The sprayer, a plural component (two-part) epoxy spraying system manufactured by Graco, is typically 

used in industrial epoxy application projects (Figure 5). 

 

19 In the September 26, 2007, KTA Inspection Report, ―Task Summary: Coating Observation Hold Points,‖ the 

inspector indicates that thinner would not be used in any ratio with the paint during either the first or second coat 

of paint. More traditional types of paint require a thinner or solvent to adjust the viscosity of the paint for proper 

application. However, the Duromar HPL-2510 two-part epoxy selected as the paint for the penstock interior did 

not require thinner to be added, as the two parts of the epoxy themselves are mixed according to a specific ratio of 

hardener to base. While a thinner or solvent was unnecessary for the actual paint mixture to be applied to the 

penstock interior, the solvent was needed to flush the sprayer system and clean equipment prior to and throughout 

the spraying process to keep the machine running smoothly for proper application of the two-part epoxy.

20 One of the 14 contractors left the site prior to October 2nd for personal reasons. 
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Figure 5. The epoxy sprayer system used within the penstock

Each epoxy component – a base and a hardener – is poured into its respective hopper, and each flows

through a heater to achieve the proper application viscosity. Pumps for each component force the heated 

material through separate hoses to a mixing block, where the hardener and base are homogeneously 

blended. This separation of heating prior to mixing is necessary because once the two components blend, 

they begin to ―set,‖ forming an epoxy bond that hardens rapidly. The combined epoxy product is then 

carried through a hose from the mixing block to the spray wand for surface application. Workers stated 

that the epoxy components used in the Cabin Creek project, once mixed, had a short ―pot life‖—a period

of approximately 20 minutes before they began to permanently harden together.

21

 

21 The epoxy product data sheet gives the ―pot life‖ as 45 minutes at 70 oF, but the workers described the period 

before the mixed epoxy began to set up as much shorter in actual working conditions.
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Solvent, such as MEK, is needed if problems arise when applying the epoxy mixture. If the combined

epoxy product was to set, it would harden within the hoses and spray wands, destroying the equipment. 

Solvent would be used to flush out the mixing block and hoses to the spray wands to ensure that the 

epoxy mixture was fully removed from the equipment and would not permanently render it unusable. 

Solvent would be introduced into these portions of the spray system using a third smaller pump on the 

back of the machine that would take in solvent from an open bucket placed on the ground at the back of 

the sprayer (Figure 6). A hose ran directly from this pump to the mixing block.

Figure 6. The solvent pump on the back side of the epoxy sprayer

The sprayer was positioned in the penstock on wheeled scaffolding, which the RPI crew called the 

―stage,‖ about 1,450 feet (442 meters) from the access door and approximately 90 feet from the west

bulkhead (Figure 7). The controls for the sprayer faced the west bulkhead, so that when a contractor was 

in position to manipulate the controls, he was looking in the direction of the access door, with the sprayer 

between him and that single point of egress. 
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Figure 7. Aerial view of equipment arrangement in work area of the penstock

In the hour leading up to the incident, five of the 13 contractors were working around the sprayer system

(Figure 8). Three of these individuals – two of whom were foremen – worked the controls of the sprayer, 

while two others were stationed on the sides, each responsible for manning a hopper. Four additional 

contractors were runners, bringing epoxy, solvent, and other equipment to and from the work area to 

assist the five at the sprayer, and one person was stationed as the ―hole watch‖ attendant at the access 

door 1,450 feet (442 meters) away.

22

 

22 Among other responsibilities, the assigned ―hole watch‖ is responsible for tracking who enters the confined space 

and the duration of time each spends within the space.
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Figure 8. Depiction of contractors working with the sprayer immediately prior to the flash fire
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The last two of the 13 contractors – besides the general foreman – were at the far end of the work area 

near the temporary west bulkhead, preparing to begin recoating the penstock interior using a wheeled 

scaffold that had been built for the crew as they used spray wands to recoat the penstock interior (Figure 

9).

Figure 9. Depiction of contractors recoating the penstock interior near the temporary west bulkhead

4.1.8 Preparation for Coating Application

In preparation for applying the epoxy, approximately 10 gallons of MEK was brought into the penstock in 

5-gallon plastic buckets to flush out the entire sprayer system prior to applying the epoxy. This flushing 

cleans out the mixing block and combined epoxy product hose lines to the spray wands and involves

pouring MEK into each of the hoppers and re-circulating the solvent through the sprayer from the hopper 
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to the discharge of the pump.23 This full flushing process ensures that all foreign matter, debris, and 

leftover epoxy products are completely removed from the equipment before new epoxy products are 

introduced. 

MEK is highly flammable and can produce hazardous atmospheres with air and be ignited under almost 

all ambient temperature conditions (NIOSH, 1998; NFPA 2007b, Table 6.2) (Section 6.5.1 details the 

hazards of MEK).

On October 2, after this flushing process was completed, the open buckets of used MEK were kept within

the sprayer area for future use. Immediately prior to the incident, at least eight buckets of epoxy and three 

buckets [about 11-12 gallons (42-45 liters)] of MEK were on the stage. One of these buckets was a 5-

gallon (19 liters) pail that sat open underneath the solvent pump on the back side of the sprayer. A 

halogen lamp sat on top of the pumps, projecting light onto the hoppers. In addition, more than 95 plastic 

buckets of base and hardener epoxy products were distributed throughout the penstock (Appendix C 

provides an inventory of epoxy and solvent within the penstock at the time of the incident).

The KTA inspector and RPI general foreman examined the penstock work area and determined that the 

contractors could begin applying epoxy. The inspector and general foreman then left the site for lunch at 

about 1:10 pm, while the other 12 RPI workers remained at the site, 11 of whom continued working 

within the penstock.

24

4.1.9 Epoxy Coating Application Problems

The application process did not go smoothly, and solvent (MEK) had to be used several times to flush out 

the equipment. Eyewitnesses reported that the sprayer was not flowing accurate hardener-to-base ratios 

 

23 This preparatory cleaning of the equipment is discussed in the Duromar epoxy application guide and the Graco 

sprayer manual as normal practice during general commercial or industrial painting prior to introducing epoxy into 

the sprayer system.

24 The twelfth contractor was the attendant stationed at the access door.
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and that its electronic display continually gave error readings, which automatically shut down the sprayer.

Because of ―fingering,‖ or uneven application of the epoxy to the surface, the contractors were able to 

spray only about a 10-foot (3-meter) area of the penstock wall interior. 25

Each time the sprayer shut down, the contractors ran MEK from the sprayer‘s solvent pump to the mixing 

block, through the two hoses of combined epoxy product to the spray wands, where the solvent flushed 

the epoxy out of the hoses into plastic buckets.

This flushing between attempts of epoxy application occurred approximately four times before one of the 

RPI foremen decided that the contractors would be unable to apply the epoxy evenly. He instructed the 

contractors to flush the entire sprayer system by circulating MEK through all the equipment in 

preparation for removing the sprayer from the penstock.

After flushing the mixing block and the spray wands, the two contractors at the west bulkhead who had 

been operating the spray wands took the buckets containing a mixture of MEK and epoxy waste to the 

sprayer area. Other members of the crew began cleaning out the sprayer by removing the epoxy products 

within each hopper. 

Another contractor brought in about 6 more gallons (23 liters) of MEK in several trips using 2-gallon (7.6 

liters) plastic buckets that had originally contained the hardener. As a result, about 11-12 gallons (42-45 

liters) of pure MEK and another 12 gallons (45 liters) of epoxy/MEK waste product [of which about 5 

gallons (19 liters) were MEK] were in close proximity to the sprayer.

At this time, two of the contractors retrieved some of the nearby buckets of MEK to flush out the sprayer 

system, while two others began walking toward the access door to retrieve even more buckets of the 

solvent. MEK was poured into the hardener side and circulated through the sprayer system. The 

 

25 ―Fingering‖ is painting jargon for uneven paint application: when a thick residue of paint is left in long vertical 

lines, like fingers, up and down a surface.
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contractors then poured MEK in the base hopper for circulation. This circulation through the base side of 

the sprayer was ongoing when the initial flash fire occurred. 

4.2 The Incident

At approximately 1:55 p.m., on Tuesday, October 2, 2007, a flash fire ignited at the sprayer in the 

immediate vicinity of the base hopper while the contractors were flushing the system with MEK. An RPI

contractor was circulating the MEK from the base hopper through the pump, discharging the solvent back 

into the hopper through a nylon hose. At the time of the ignition, the contractor was holding the end of the 

hose equipped with a metal fitting inside the base hopper; he reported witnessing the initial flash arising 

from the interior of the hopper. The burning solvent forcefully erupted from the hopper and sprayed onto 

the contractor and the surrounding area. The flash fire caught the contractor‘s sleeve on fire and quickly 

engulfed the buckets of MEK. Another contractor, who left the work area to retrieve portable fans to help 

dissipate the strong MEK odor, was about 40-50 feet (12-15 meters) from the sprayer when the fire 

ignited. Two others, on their way out of the penstock to retrieve more MEK, heard a loud rumble; they 

turned in the direction of the noise and saw a flash of fire that seemed to roll toward them. These 

eyewitnesses reported that the fire appeared to come from the base hopper.

This rapidly growing fire separated the contractors who were standing on either side of the equipment. 

The five contractors who were on the far side of the sprayer found their exit blocked by the fire and were 

unable to escape. The trapped men shouted for fire extinguishers.

4.3 Emergency Response

4.3.1 Fire Extinguishers

No fire extinguishers were staged near the sprayer where the initial fire started. After the initial flash, the 

fire died down enough for those trapped behind the sprayer to communicate with the survivors on the 

other side. Those trapped instructed the others to retrieve extinguishers. The contractors on the side of 
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sprayer with access to the entrance ran about 1,450 feet (442 meters) down the penstock to retrieve the 

fire extinguishers, which were located outside of the penstock. 

While they ran for the access door, several flash fires ignited and loud booms reverberated down the 

penstock as the initial fire ignited the solvent and caused the epoxy buckets surrounding the sprayer to 

burst. The fire increased in size and intensity and spread to additional epoxy buckets in the vicinity of the 

sprayer. The trapped men retreated uphill, away from the sprayer and farther up into the penstock.

With extinguishers in hand, two of the crew ran back inside toward the fire and sprayer with the intention 

of putting out the fire. The thick black smoke reduced their visibility to almost zero and made breathing 

difficult; as a result, they could not get near enough to the sprayer and burning epoxy products to 

effectively extinguish the fire. This initial attempt, and all additional re-entries the work crew made to 

extinguish the fire, failed.

4.3.2 Initial 9-1-1 Call

One of the crew members who retrieved the first two fire extinguishers from outside the penstock handed 

the extinguishers to his coworkers before running to the nearest phone, located at the Cabin Creek 

powerhouse entrance east of the penstock. He called the Cabin Creek power house control board, 

notifying them of the penstock fire and need for 9-1-1 assistance.

Clear Creek County Emergency Dispatch received the first 9-1-1 call from an Xcel control room operator 

at 2:03 p.m. The caller told the 9-1-1 operator that there was a fire in the penstock, but did not explain that 

the penstock was a confined space or that specialized rescue personnel and equipment would be required 

to fight the fire and rescue trapped workers.26 The 9-1-1 operator immediately broadcast a request to Clear 

 

26 The caller told the 9-1-1 operator that there was ―a fire in our penstock...in our tunnel...outside on our surface 

deck, outside of the plant...on the surface.‖ 
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Creek County Emergency Services27 to respond to the Cabin Creek site, indicating that there was a fire on 

the ―surface deck.‖

The RPI worker also called the company corporate office to notify management of the emergency. He 

then went back to the access door of the penstock and found that the RPI general foreman and KTA 

inspector had arrived.

During this time the trapped workers used a radio to remain in communication with the crew that 

escaped.

28

4.3.3 Emergency Responders Arrive

Upon arriving at the Cabin Creek site, emergency responders established an Incident Command structure. 

At 2:11 p.m., the first Clear Creek County Sheriff‘s officers arrived on the scene, followed shortly by a 

volunteer paramedic and firefighter from the Clear Creek County Fire Authority (CCFA). These 

responders saw no signs of a surface fire when they arrived. Xcel and RPI employees quickly informed 

them that the fire was inside the penstock and that several workers were trapped. At 2:20 p.m., the 9-1-1 

center broadcast an update indicating that the fire was 1,000 feet (305 meters) inside the penstock tunnel 

and below ground. The message also informed responders that they would need 1,000 feet (305 meters) of 

hose and the equipment necessary to fight an underground fire.

The CCFA responders lacked the necessary equipment and resources to safely enter the penstock; they 

were also concerned that they lacked the appropriate training to perform rescue within the confined space.

 

27 Clear Creek Fire Authority (CCFA) is a consolidated fire protection and emergency service agency serving the 

municipalities of Empire, Georgetown, Idaho Springs, and Silver Plume, and the unincorporated lands of Clear 

Creek County previously represented by the Clear Creek Emergency Services District (ESD). CCFA‘s territory 

includes I-70 (Colorado‘s primary east-west transportation corridor); Clear Creek (a rafting river); four 14,000-

foot (4,300 meters) peaks; two ski areas; several hundred abandoned mines; and residential and business districts. 

(Colorado Division of Emergency Management, http://dola.colorado.gov/dem/operations/operations.htm, accessed 

July 30, 2010).

28 The CSB determined this timeline by correlating events discussed in interviews with security video footage of the 

area outside the penstock.
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4.3.4 Call for Mutual Aid

CCFA personnel en route to the site, based on information broadcast over their radios (i.e., that the fire 

was located deep inside the penstock and that workers were trapped), contacted Denver‘s West Metro Fire 

Protection District (West Metro) to request firefighting and rescue assistance.29 West Metro Emergency 

Response personnel are located on the west side of Denver, approximately 1 hour and 15 minutes travel 

time (about 45 miles or 72 kilometers) from Cabin Creek.

At one point, firefighters requested and received the MSDSs from RPI.

At 2:30 p.m. the Incident Commander contacted Climax Molybdenum Company‘s (Henderson Mine) 

mine rescue team to request support in rescuing the stranded workers.

4.3.5 Attempted Entry by Early Rescuers

Approximately 45 minutes after the initial fire, but before West Metro or Henderson Mine emergency 

personnel arrived, four Clear Creek firefighters entered the penstock to assess the fire and the prospect of 

rescuing the five trapped RPI employees. Wearing protective fire-fighting clothing and self-contained 

breathing apparatuses (SCBAs), they used a small gasoline-powered all-terrain vehicle (ATV)30 to 

explore the penstock. Because of the smoke and lack of visibility, they were able to move only about 200 

feet (61 meters) into the penstock before they stopped and returned to the entrance, concluding that they 

were unable to extinguish the fire and/or rescue the trapped workers. CCFA did not attempt further entry 

into the penstock until after Henderson Mine rescue personnel cleared the penstock.

 

29 West Metro and CCFA have a Mutual Aid agreement for technical firefighting and confined-space rescue.

30 The ATV was placed in the penstock at the beginning of the project to transport personnel and supplies 

throughout the steel portion to be recoated.
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4.3.6 Stranded Workers Still Communicating 45 Minutes into Incident

Radio communications between the trapped contractors and those outside the penstock continued for 

about 45 minutes after the initial flash fire. The trapped workers were instructed to move to the upper end 

of the penstock, away from the burning sprayer, epoxy, and solvent.

4.3.7 Emergency Responders Evaluate Further Entry into the Penstock

West Metro arrived at the Cabin Creek site around 3:40 p.m., but because they did not know about the

conditions inside the penstock—whether explosive hazards existed—they did not enter to fight the fire or 

attempt rescue. Instead, they joined CCFA and another rescue group, Alpine Rescue, at the top of the 

penstock (the mushroom). Upon arrival at the mushroom, West Metro was told that breathing air bottles 

and respirators, a light, and a radio were lowered down into the vertical portion of the penstock in the 

hopes of reaching the trapped contractors. This activity posed its own difficulties due to the winding potholed road leading to the mushroom and the challenges of using the mushroom‘s access hatch.

4.3.8 Emergency Responders Enter the Penstock

The first of two Henderson Mine rescue teams arrived shortly after 4:00 p.m. and prepared to enter the 

penstock at the access door.

Sometime between 4:45 p.m.and 5:30 p.m., Xcel operations personnel reversed the penstock ventilation 

fans to try and reverse the penstock airflow and draw the smoke away from the stranded workers.

Henderson Mine responders entered the penstock at 5:45 p.m. After verifying that the fire had burned out,

they continued up the penstock to determine if any of the workers had survived. They found the first body 

approximately 100 feet (30.5 meters) uphill of the fire. The four remaining were located even further 

uphill, near the point at which the penstock‘s incline abruptly steepens. Post incident, it was determined at 

all five died of asphyxiation shortly after radio communications ceased, at approximately 2:45 p.m.
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5.0 Incident Analysis

The CSB found that numerous safety issues collectively contributed to the October 2, 2007, incident.

5.1 Pre-Incident Events

Insufficient ventilation, improper equipment for fire prevention, and a tight schedule created an unsafe 

work environment even before the epoxy application activities began.

5.1.1 Insufficient Ventilation

Adequate ventilation was an important safety issue of the penstock work environment. The work area 

being sandblasted and coated was sandwiched between two wooden bulkheads built to confine the 

sandblasting medium and epoxy coating materials, and to isolate the work area space of the penstock. 

Ventilation and the control of nuisance dust was to be accomplished using two desiccant-style 

dehumidifiers that would force air into the space at a rate of approximately 13,000 cubic feet per minute 

(CFM).31 Additionally, a 12,000 CFM dust extractor was to be used that would pull air out of the 

penstock and remove dust particles before discharging the air outside. This ventilation setup, if operating 

optimally, equated to approximately 4.4 air changes per hour (ACH)32 in the work area between the two 

bulkheads.33 In constrast, the Flammable and Combustible Liquids OSHA standard requires a room that 

simply stores flammable and combustible liquids be ventilated at a rate of six air changes per hour in 

order to prevent explosive vapors from accumulating [29 CFR 1910.106(d)(4)(iv)]. None of the 

 

31 The inlet air was delivered into the work area via a 20-inch (52-centimeter) diameter flexible plastic supply duct 

magnetically attached near the floor of the metal-walled penstock. The return duct located near the access door 

directed the air from the penstock through the dust collector before it was discharged to the outside atmosphere. 

During sandblasting, additional portable blowers and fans moved the dust-laden air down the penstock toward the 

east bulkhead near the access door. The additional portable blowers or fans were not used while the epoxy coating 

was being applied.

32 The number of times air is replaced in an hour.

33 Volume of Air: 13,000 CFM x 60 min = 780,000 CFH; Volume of Space: (6 ft)2

x 1560 ft x π = 176,432 ft3; Air 

Changes: 780,000 CFH/176,432ft3 = 4.4 air changes per hour
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ventilation design documents obtained by the CSB indicated any analysis of the adequacy of 4.4 air 

changes per hour in relation to the dissipation of flammable vapors in the work space. The penstock‘s 

ventilation setup was designed soley for the purpose of ensuring the penstock ambient conditions were 

optimal for the sandblasting and epoxy application activities.

After using MEK to clean the spray wands on the scaffold near the west bulkhead, one of the contractors

left the work area to get a fan to dissipate the buildup of solvent ―fumes‖ that he smelled through his 

respirator. He told the CSB that, as he squeezed past the scaffold holding the sprayer, there was ―no air 

movement at all‖ in the vicinity of the sprayer. Post-incident, OSHA cited RPI for not ensuring 

ventilation equipment provided acceptable confined space entry conditions [OSHA 21 Mar 2008, 

inspection 310470034, citation 2(8)]. While adequate ventilation is a necessary component for managing 

the hazards of confined space work, the CSB has concluded that ventilation alone was insufficient to 

safely control the risks of using flammables in the open atmosphere of the penstock.

5.1.2 Improper Equipment Choices for Fire Prevention

Penstock recoating equipment choices made by RPI personnel, including management officials, increased 

the likelihood of a fire. 

5.1.2.1 Decision not to Use Heated Hose Lines

The CSB determined that the primary reasons for the epoxy application difficulties were due to the 

inability to achieve and maintain the necessary temperatures of the epoxy components for application, 

which likely would have been avoided had heated hose lines been used. Heated hoses are often used in 

specialized industrial painting projects to overcome the negative impact of temperature, which can affect 

the viscosity of the epoxy and thus the quality of the coating application. However, a decision was made 

to use regular spray hoses instead, despite the penstock ambient and surface temperatures being below

recommended levels for proper epoxy application.

The product data sheets for the epoxy base and hardener, RPI provided to Xcel as a part of its bid 

submission package, state that the minimum surface temperature during application must be no colder 
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than 60 oF (16 oC). However, in the week leading up the incident, ambient temperatures averaged 58 oF 

(14 oC), and on October 2, the KTA inspector recorded the interior surface temperature of the penstock as 

54 oF (12 oC). The General Application Guidelines for the epoxy, also included in the bid package, 

indicate that the base and hardener components be stored in ―a warm area where the temperature remains 

between 60-90 oF (16-32 oC). Cold products are very viscous and will be very difficult to mix and apply.‖ 

While the epoxy components were initially stored in a heated trailer, more than 95 buckets of epoxy were 

brought into the penstock and staged in groups along 1,450 feet (442 meters) of the penstock‘s cold steel 

floor. 

The RPI work crew reported that the sprayer was having trouble heating the cold material, particularly the 

base, due to its thickness and initial cold temperature. When mixing the two epoxy components together, 

the combined product should have been between 70-80 oF (21-27 oC). A RPI contractor taking 

temperature readings of the unmixed products within the hoppers with a laser gauge immediately prior to 

application stated that the temperature readings of the base that day reached no greater than ―45 o, 47 o.‖ 

Furthermore, the sprayer had difficulties maintaining the required epoxy temperature for an extended 

period. When workers circulated the two epoxy components several times through each side of the 

sprayer and the attached heaters, the limited quantity of each component within the sprayer system was 

able to achieve the requisite temperature.34 However, after the heated components were sent to the mixing 

block for blending, additional (cold) epoxy had to be added to each hopper to keep the flow of combined

product out of the spray wands consistent. But additional time was needed for the cold epoxy to circulate 

through the heaters to warm up to the appropriate application temperature. The CSB concluded that the 44 

feet (13 meters) of hose from the sprayer to the mixing block and the additional 40-60 feet (12-18 meters) 

of hose from the mixing block to the spray wands was too great a distance to maintain the requiste 

 

34 Testimony from an RPI crew member stated that the crew had to circulate the material multiple times to get the 

paint to the requisite temperature. 
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temperature as cold epoxy was added to the sprayer and then passed through hose that ran along the cold 

penstock floor to the area being recoated.

35

The RPI vice president discussed the plan to use in-line heated hose as late as five days prior to the 

incident, yet they were not incorporated into the equipment setup within the space. The lack of heated 

hose, in combination with the extensive length of hose required to complete the application work, 

contributed to the crew‘s inability to keep the epoxy at the appropriate temperature for proper epoxy 

application. As a result, the sprayer would not function effectively and the crew was forced to repeatedly

flush the hoses from the mixing block to the spray wands with MEK between each failed attempt, which

contributed to the buildup of MEK in the atmosphere.

5.1.2.2 Electrical Safety Precautions not Met

Equipment used to handle flammable material must be properly bonded and grounded, and hoses must be 

electrically conductive. These electrical safety precautions were not met on the day of the incident; 

specifically, the CSB determined that some of the hose chosen for the penstock job was likely nonconductive.

Non-conductive flexible hoses are not recommended for use with flammable liquids due to their staticaccumulation capabilities unless, at a minimum, all conductive couplings (e.g., end fittings or connectors) 

are bonded and grounded (NFPA 77, 2007a, Section 8.4.3.2). 

While most of the hoses around the sprayer were destroyed in the fire, an examination of the equipment 

post-fire uncovered the remains of the hose used to circulate solvent through the hardener hopper and its 

associated equipment still attached to the sprayer, including a hose connector (metal swivel) and the inner 

woven metal sheath. The hose used to circulate solvent through the base side of the sprayer was destroyed 

 

35 An RPI crew member with experience working with this product recommended that the paint come out of the 

spray wands at a temperature of 110 oF for correct application. 
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in the fire and the inner woven metal sheath was not observed to be attached to the sprayer was not found

in the surrounding debris. Due to the lack of an inner metal sheath, the CSB concluded that the base side 

solvent hose was likely non-conductive and did not establish appropriate bonding to allow for the 

dissipation of static electricity on the metal hose connector. (Appendix D.1). A static charge likely built 

up as solvent travelled through this hose; eventually an electrical spark between the hose connector and 

the metal base-side hopper of the sprayer likely resulted in the initial flash fire (Section 5.2.2 and 

Appendix D discuss this ignition scenario in detail). To prevent static charge buildup, conductive, rather 

than non-conductive, hose should have been used with the sprayer.

5.1.2.3 Use of Unsafe Lighting

Unsafe lighting was also used within the penstock when flammables were present. RPI‘s ―Spraying 

Equipment and Operations‖ policy within its IIPP states: ―Explosion proof [sic] portable lamps must be 

used to illuminate the spray areas.‖ However, the penstock spray area, including where the sprayer system 

was setup, was illuminated with a variety of lighting, not all of which was explosion-proof. Specifically, 

several halogen lamps were placed around the sprayer, with one resting on top of the sprayer pumps at the 

time of the incident (Figure 10).

Figure 10. Remains of the halogen light sitting atop the sprayer inside the penstock (left); the same 

remains being compared to an exemplar halogen light (right).

Halogen light frame
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Equipment and supplies needed for the penstock project were planned by the onsite foremen, the RPI 

shop manager, and RPI upper level management in advance of the work crew‘s activities inside the 

penstock. While the ignition of MEK vapor from the heat of a halogen light was determined to be a less 

likely ignition scenario (Appendix D), the CSB concluded that this unsafe lighting choice was a serious 

safety risk when used in conjunction with the introduction of flammables within a confined space. 

5.1.2.4 No Fire Extinguishers Within the Work Area

Fire extinguishers were not immediately available to the contractors after the initial flash fire because 

they were not situated by the sprayer and within the work area. Contractors had to go approximately 

1,450 feet (442 meters) – a length of over four football fields – to the exit of the penstock and retrieve 

extinguishers after the initial fire. RPI‘s ―Fire Protection and Prevention‖ policy, within the IIPP, states

that fire extinguishers ―must be in close proximity to all painting operations.‖ While ―close proximity‖ is 

not defined, it is reasonable to conclude that 1,450 feet (442 meters) does not meet the definition.

Additionally, NFPA 851, Recommended Practice for Fire Protection for Hydroelectric Generating Plants 

(2005), states that fire suppression equipment should be ―provided where risk of fire exists‖ and ―located 

for easy access‖ (NFPA 851, section 8.8.1). It goes on to state ―Portable fire extinguishers of suitable 

capacity should be provided where...flammable liquids are stored or handled‖ (NFPA 851, section 

8.8.2).36 Had extinguishers been present at the location of the sprayer work activities, the solvent flash fire 

likely could have been suppressed or extinguished at the time of initial ignition prior to the combustion of 

the larger quantities of the epoxy products.

 

36 Section 1.3.2 of NFPA 851 states that the recommendations within the Recommended Practice are intended for 

new installations, but notes that ―the recommendations contained in this document represent good industry practice 

and should be considered for existing installations.‖
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5.1.3 Scheduling and Production Pressures

A tight 10-week project completion schedule, severe weather concerns, several unplanned work delays, 

and perceived production requirements placed RPI employees under intense pressure to complete the 

recoating work. These stressors contributed to a rushed work pace on the day of the incident, which likely 

affected the crew‘s ability to focus on safety. Decisions made in haste and under stress can often have 

deleterious side effects, including inadvertent step deletion or heavy focus on one issue while minimizing 

the significance of others (Dismukes, Berman, & Loukopoulos, 2007, p.261). Evidence indicates that the 

RPI workers experienced a rushed work pace the morning of the incident, and safety was likely 

negatively impacted as a result.

For a power plant like the Xcel Cabin Creek site, the downtime of the penstock would be costly. An RPI 

foreman involved in the initial planning of the recoating project confirmed that the project was set on a 

―short schedule,‖ where work would be conducted on a 24-hour/7-days-a-week schedule until completed 

in order to be able to accomplish the recoating project in shortest time period possible. In addition, the 

vice president of RPI noted the very tight schedule in emails during the planning phase of the project, 

questioning if only one coat of epoxy, rather than two, could be applied to the floor of the penstock to 

accelerate the work pace and decrease curing time of the epoxy. 

The project‘s timing was also one of five items emphasized as problematic in the Xcel ―Major Items of 

Concern‖ penstock project planning document (Section 4.1.1), written by an Xcel civil engineer who 

noted that the time it would take to drain the penstock, coat the interior lining, allow the epoxy to cure, 

and refill the penstock for hydroelectric power would be difficult to accomplish, even in the best 

conditions, within the allotted 10-week schedule. He added that the weather during the time of year the 

penstock would be recoated – September through November – would ―not lend itself to the best of 

conditions.‖ 

As the project began, several delays in the initial work tasks constrained the already tight schedule 

significantly from the initial timeline RPI submitted to Xcel with its bid submission documentation. A 
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compressor was blown out during the sandblasting portion of the work. The RPI crew experienced 

electrical problems, blowing out a few of the electrical ―spider‖ boxes and lighting, which required repair 

and replacement; and the contractors had to spend extra time sandblasting to remove the necessary 

amount of old liner prior to recoating. Specifically, the submitted schedule stated that the first quarter of 

the 1,560 feet (475 meters) of the penstock being recoated would be sandblasted and coated by the first of 

October; but the crew was just making its initial application attempts on October 2, over one week behind 

schedule.

In interviews with the CSB, the RPI employees confirmed that they were behind schedule before they 

even began the epoxy application process. Penstock crew personnel stated that they heard the general 

foreman report to RPI headquarters that a number of work tasks were completed before they actually 

were. The day of the incident, eyewitnesses stated that the general foreman was anxious about the crew‘s 

progress and was pushing to get the recoating portion of the project underway. A number of the 

employees stated that with past projects they typically had regular safety meetings to review work tasks 

and safety concerns, but that the penstock job was different in that such safety discussions were not held 

as often, nor were they as focused on safety, as in previous jobs. According to the workers, any

discussions held the morning of the incident focused on preparing equipment within the penstock for the 

recoating work, not on any safety risks inherent with the work, such as with using a flammable within a 

confined space, nor on any steps taken to mitigate those risks, such as ensuring fire extinguishers are 

located within close proximity to the sprayer system. Instead, the employees reported that the focus that 

day was solely on getting the epoxy on the walls. 

In addition to the work delays and schedule pressures, RPI employees reported that the company used 

unofficial financial incentive programs – both in the past and in this recoating project – to ensure that 

work was completed in a timely manner. A number of the survivors asserted that if the crew finished the 

project on time or earlier than scheduled, the general foreman would receive a financial bonus. Some 

contractors stated that the general foreman would share the bonus with the hardest working members of 
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the crew. Employees testified that this incentive was based purely on the timeliness of work completion. 

Incentive programs like these are common in many workplaces; however, attention must be given to 

ensure that such rewards do not have unintended negative consequences, such as a decline in work quality 

or safety in order to ensure on-time work progress (Hopkins, 2005, p.51 – 60; Hopkins, 1999, p.13 and 

94).

5.2 Incident Events

The use of solvent within the confined space of the penstock to clean the sprayer created a flammable

atmosphere. A static spark most likely ignited the flammable atmosphere within the sprayer hopper, 

resulting in a flash fire that quickly intensified as additional solvent and the combustible epoxy 

surrounding the sprayer ignited. The rapid spread of fire and toxic smoke from burning epoxy prevented 

the workers uphill of the sprayer from exiting through the penstock‘s only egress point, resulting in their 

deaths. 

5.2.1 Unsafe Sprayer Flushing Method Contributed to a Flammable 

Atmosphere

On October 2, the contractors flushed the entire sprayer system with MEK while it was still within the 

penstock‘s confined space, creating a flammable atmosphere within the work area. Flushing the sprayer 

system with solvent outside the penstock could have avoided creating this flammable atmosphere, as none 

of the equipment, with the exception of the mixing block itself and the hoses going to the spray wands, 

required immediate flushing with a solvent. It is only when the hardener and base epoxy components are 

combined that they react with each other and solidify (Section 4.1.7). The potential for a flammable 

atmosphere to develop would have been greatly reduced, had the solvent only been used to flush the 

mixed epoxy material from the hoses extending from the mixing block to the spray wands.

5.2.2 Most Probable Ignition Source

The CSB concluded that the fire inside the penstock was most likely ignited by a static spark that 

originated from the electrically isolated (ungrounded) metal swivel connector attached to one end of the 
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non-conductive hose being handheld inside the base hopper of the sprayer as MEK was being flushed 

through (Appendix D.1). The CSB calculated that the MEK concentration in the vapor surrounding the 

metal swivel connector was between 7.6 and 9.1 volume percent, which is well within the flammable 

limits of 1.8 and 11 volume percent, based on the MEK vapor-liquid equilibrium concentration adjusted 

for penstock environmental conditions (Appendix E). The CSB determined that the MEK circulation flow 

through the sprayer was likely capable of developing a charging current, accumulating stored energy on 

the electrically isolated metal swivel connector and producing incendiary sparks of sufficient magnitude 

to ignite the flammable MEK vapor (Appendix F).

While the CSB determined that a static spark was the most probable ignition source, two other potential 

ignition sources could not be completely ruled out:

An electrical arc produced inside the base hopper by a stray current inside the sprayer system 

(Appendix D.2), or

Autoignition of flammable MEK vapor by the hot bulb of the portable halogen lights 

positioned above the sprayer (Appendix D.3)

Fire damage to the sprayer and associated equipment precluded the CSB from completely dismissing a 

stray current arc as the ignition source. The two electrical discharge ignition scenarios (static spark and 

stray current arc) are similar with respect to the location of the spark (metal swivel connector attached at 

the end of the hose) and vapor composition constraints limited to the base hopper. However, since a static 

spark requires a non-conductive hose and a stray current arc requires a conductive hose, these two 

electrical discharge mechanisms are mutually exclusive. Available evidence indicates that the base 

hardener hose was constructed from a non-conductive (nylon) material and the end connector was 

attached without any internal electrical bonding. 

Conflicting testimony and fire damage to the sprayer‘s heaters and control panel also meant that the CSB 

could not conclusively verify whether the MEK was being heated as it circulated through the sprayer at 
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the time the fire occurred. Thus, the CSB could not totally eliminate the possibility that the MEK 

temperature was hot enough to develop a flammable atmosphere above the sprayer, where the hot bulb 

surface from the portable halogen lights could have caused autoignition of the flammable MEK vapor. 

However, witnesses stated that the fire originated inside the base hopper and the CSB considered it 

unlikely for the fire to have been ignited at the halogen lights with a flame front traveling back to the 

hopper without being observed. 

Three additional ignition scenarios were evaluated and eliminated as probable ignition sources: hot 

surface ignition by the sprayer heater(s) (Appendix D.4); compression ignition inside one of the sprayer 

piston pumps (Appendix D.5); or electrical spark from the heater control box (Appendix D.6). In 

summary, although either autoignition by the halogen bulb or a stray current arc were both possible 

ignition sources, evidence suggests that the most likely ignition source was a static spark between the 

metallic end connector on the non-conductive hose and the wall of the hopper.

To reduce the risk of fire or explosion, fire safety measures should employ protections aimed at 

eliminating at least two legs of the fire triangle 37: oxygen, fuel, and ignition source (Scarbrough, 1984, 

pp.521-552). Potential ignition sources are often difficult to identify and control in situations where 

flammable liquids are being used. Because oxygen is normally present and difficult to remove, especially 

when people need to employ or interact with equipment that uses flammable liquid, fire safety measures 

stress the need to keep concentrations of flammable vapors well below the LEL38 to prevent flash fires 

and explosions. This is especially important in a confined space where the number of air changes can be 

 

37 The fire triangle is a concept used to explain the three conditions – heat, fuel, and oxygen – that must be present 

for combustion. 

38 LEL is defined as ―that concentration of combustible material in air below which ignition will not occur.‖ 

―Recommended Practice for Handling Releases of Flammable and Combustible Liquids and Gases, NFPA 329 

(2005). The terms lower explosive limit (LEL) and lower flammability limit (LFL) have different definitions but 

are commonly used interchangeably. This report will use LEL except where citing other sources that use LFL in 

their standard or regulation. The OSHA Permit-Required Confined Space Standard 29 CFR 1910.146 uses the 

term LFL in its provisions.
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limited, causing flammable vapors to quickly concentrate. In this incident, a lack of fire safety measures 

to control or eliminate the concentrations of flammable vapors being generated during the flushing 

operation resulted in the penstock fire igniting when a suitably energetic ignition source appeared. 

5.2.3 Flash Fire Becomes Sustained Toxic Fire, Trapping Workers

Approximately 16 gallons (61 liters) of MEK and at least 30 of the 95 buckets of epoxy39 were destroyed 

in the fire. The initial flash fire involved only the solvent being used directly within the hopper; however, 

the large amount of solvent surrounding the sprayer, as well as numerous buckets of epoxy hardener and 

base, caused the flash fire to grow into a sustained, intense toxic fire. 

Neither the MEK nor the epoxy components needed to be in the penstock in such large quantities. The 

amount of solvent required to flush the lines from the mixing block to the spray wands was significantly 

less than what was needed to clean out the entire sprayer system. 

Had the decision been made to remove the sprayer from the penstock prior to flushing – a decision that 

should have been made by management prior to any onsite activities related to the penstock recoating 

project – the creation of a flammable atmosphere likely would have been avoided. And, had there not 

been additional MEK in buckets surrounding the sprayer, the initial flash fire likely would not have 

intensified. Finally, the subsequent ignition of the combustible epoxy components turned the growing fire 

into a toxic one.40 This sustained fire prevented the trapped contractors from climbing around the sprayer. 

They had no choice but to run up the penstock, away from the burning products and their only exit.

 

39 Because the fire burned many of the plastic buckets, leaving only the metal handles, it was impossible to discern if 

these melted buckets were 2-gallon hardener or 5-gallon base buckets. Therefore, a more precise quantity (in 

gallons) of epoxy burned in the fire could not be determined. 

40 The MSDS for the epoxy hardener states that ―heat and fire can generate toxic or irritating decomposition 

products that may cause a health hazard. Sudden reaction wand [sic] fire may result if product is mixed with an 

oxidizing agent‖ (Duromar HPL-2510 Hardener, 7/2/2007). The MSDS for the epoxy base states that ―heat from 

fire can generate flammable vapor and decomposition products that may cause a health hazard.‖ The base is also 

noted as a ―known human carcinogen‖ (Duromar HPL-2510 Base, 3/21/2007). 
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6.0 Confined Space

The penstock recoating project was hazardous in that introducing and using flammable and toxic 

chemicals within a confined space presents numerous safety risks. The unique features of the penstock, 

including its extensive size and lack of a secondary point of egress, amplified the danger. Extensive and 

detailed pre-job safety planning was needed to evaluate and address the hazards inherent in this 

maintenance work. 

The CSB concluded that Xcel, RPI, and KTA initially recognized the Cabin Creek penstock as a permitrequired confined space, but did not treat it as such during the penstock project. As a result, the 

companies did not effectively coordinate and plan to control the hazards inherent in the recoating work. 

Nor did RPI re-evaluate the hazards when working conditions changed inside the penstock, such as the 

introduction of flammable MEK into the work area. Xcel‘s and RPI‘s lack of sufficient planning and 

coordination for the hazardous recoating work within the confined space was causal to the incident. 

6.1 Penstock is a Permit-Required Confined Space

The Cabin Creek penstock is a permit-required confined space, as defined by OSHA: it is large enough 

and so configured that an employee can bodily enter and perform assigned work, it has limited or 

restricted means for entry or exit, and it is not designed for continuous human occupancy [29 CRF 

1910.146(b)]. The penstock‘s 12-foot (4-meter) diameter space is large enough for workers to enter and 

work inside; entry and exit are feasible only through the temporary 4 by 4-foot (1.2 by 1.2-meter) opening 

cut at the lower end and, when generating hydroelectric power, the penstock is full of flowing water. The 

penstock also meets an additional criterion: it ―contains or has the potential to contain a hazardous 

atmosphere,‖ making it not just a confined space, but a permit-required confined space [29 CRF 

1910.146(b)]. A hazardous atmosphere, as defined by the OSHA Permit-Required Confined Spaces 
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Rule,41 is one that may expose employees to the risk of death; incapacitation; impairment of ability to 

self-rescue; injury; or acute illness from flammable gas, vapor, or mist in excess of 10 percent of its lower 

flammability limit (LFL).

42 OSHA requires employers to evaluate their workplace to determine if any 

confined spaces meet the criteria for a permit-required confined space [29 CFR 1910.146(c)(1)]. Despite 

initial recognition that the penstock was a permit-required confined space, neither Xcel nor RPI treated 

the penstock as a permit-required confined space while the recoating work was being conducted.

6.1.1 Initial Evaluation of the Confined Space Indicated a Permit-Required 

Program was Necessary

In early 2007, an Xcel safety consultant, at the request of the penstock recoating team, prepared the 

―Safety and Health Hazard Assessment Survey‖ for abrasive blasting inside the penstock, which lists

confined space entry as one of the potential health hazards associated with the recoating work, in 

conjunction with applying epoxy or other surface coatings. The survey states that ―a confined space air 

monitor is required,‖ which is a key safety requisite in a permit-required confined space program. While 

this document was made part of the bid package and sent to potential contractors, Xcel did not implement 

a permit-required confined space program or issue permits for its personnel who entered the penstock on 

numerous occasions for inspection and maintenance. 

In addition, a KTA inspector completed a separate ―Initial Pre-Job Hazard Assessment,‖ which it 

submitted to Xcel on September 24, 2007, for abrasive blasting inside the penstock, explicitly indicating 

that the penstock was a permit-required confined space. 

 

41 In addition, the OSHA Permit-Required Confined Space rule states that these risks follow from one or more of 

the following causes: (1) flammable gas, vapor, or mist in excess of 10 percent of its LFL; (2) airborne 

combustible dust in a concentration that meets or exceeds its LFL; (3) atmospheric oxygen concentration below 

19.5 percent or above 23.5 percent; and/or (4) atmospheric concentration that could result in employee exposure in 

excess of its dose or permissible exposure limit.

42 The terms LEL and lower flammability limit (LFL) have different definitions but are commonly used 

interchangeably. This report uses LEL except where citing other sources that use LFL in their standard or 

regulation. The OSHA Permit-Required Confined Space Standard 29 CFR 1910.146 uses the term LFL in its 

provisions.
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RPI wrote a number of partially completed confined space permits with air monitoring logs between 

September 11 and October 2, 2007, where the crew indicated that continuous air monitoring was required 

inside the penstock—another element of a permit-required confined space program.43,44

Although Xcel, RPI, and KTA acknowledged that elements of a permit-required space were necessary for 

the penstock work, the companies did not take the steps necessary – and required by OSHA – to manage 

the risks inherent in the space.

6.1.2 The Known Work Activities in the Penstock Necessitated a PermitRequired Confined Space Program

The potential atmospheric hazards related to future work activities in the penstock known to Xcel and RPI 

during the early stages of the penstock recoating project should have triggered the application of a permitrequired confined space program. These potential atmospheric hazards in the confined space included 

High carbon monoxide (CO) levels that caused air monitors to alarm and required the 

penstock to be briefly evacuated;

Fumes created from welding conducted inside the penstock by an Xcel employee on two 

occasions;

Irritating dust and breathing hazards created by abrasive blasting; and 

Flammable vapors generated while using MEK to flush and clean the sprayer. 

 

43 The logs typically listed only the gas detector readings for oxygen written on a page taken from RPI‘s multipage 

confined space permit form. No other pages of the permit form were completed 

44 Even number of the unsuccessful bidders for the penstock recoating project identified the penstock as a permitrequired confined space in their submissions to Xcel. A proposal from a prospective bidder on the recoating 

project stated that the penstock would be considered a permit-required confined space when certain activities were 

undertaken, such as abrasive blasting, abrasive cleanup, and epoxy application.
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6.1.3 Permit-Required Confined Space Inadequately Declassified

Once work began at Cabin Creek, Xcel, RPI, and KTA treated the penstock as a non-permit-required 

space; however, the companies did not take the OSHA-required steps to formally declassify the penstock 

to a non-permit confined space. Indeed, had they taken the requisite steps to attempt to declassify the 

penstock, they would have determined that the penstock space could not have been safely declassified.

OSHA‘s Permit-Required Confined Spaces Rule states that if an employer wishes to reclassify a permitrequired confined space as a non-permit confined space, the employer must develop monitoring and 

inspection data demonstrating that the space poses no actual or potential atmospheric hazards, and this 

data must be documented by the employer [29 CFR 1910.146(c)(7), 1910.146(c)(7)(i), 

1910.146(c)(5)(i)(F)]. Additionally, the employer is required to ―document the basis for determining that 

all hazards in a permit space have been eliminated, through a certification that contains the date, the 

location of the space, and the signature of the person making the determination‖ [29 CFR 

1910.146(c)(7)(iii)]. Neither RPI nor Xcel provided the CSB with a documented basis for declassifying 

the penstock space as non-permit required.

More important, the penstock‘s unique size – more than 4,000 feet (1200 meters) long – makes it an 

exception in the Permit-Required Confined Spaces Rule for declassifying a space. The rule states that ―if 

isolation of the space is infeasible because the space is large or part of a continuous system (such as a 

sewer), pre-entry testing shall be performed to the extent feasible before entry is authorized and, if entry 

is authorized, entry conditions shall be continuously monitored in the areas where authorized entrants are 

working‖ [29 CFR 1910.146(d)(5)(i)]. The American Public Power Association (APPA), an industry 

organization for public utilities – of which Xcel is not – instructs its member organizations as follows: ―If 

a hazard increasing work activity is to take place in a confined space (i.e., welding, painting, working 
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with solvents and epoxy), the air in the space shall be continuously tested for the presence of flammable 

or toxic gases and vapors or insufficient oxygen‖ (APPA, 2007).45

The expansive size of the penstock required continuous monitoring at the location of the work, which at 

the time of the incident was 1,450 feet (442 meters) from the access door; this continuous monitoring 

within the penstock was not being performed by the RPI crew, the KTA inspector, or any Xcel personnel. 

The penstock‘s large size and the companies‘ lack of documented basis for declassifying the space require 

it to be treated as a permit-required confined space.

6.2 Lack of Pre-Job Safety Planning for Hazards 

Despite a lengthy period of over one year devoted to pre-job safety planning for the recoating project of 

the Cabin Creek penstock, the CSB noted that serious hazards identified by the Xcel recoating project 

team and RPI management were not addressed before work began (Section 4.1).

In early 2007, Xcel completed the ―Safety and Health Hazard Assessment Survey‖ for the recoating

project; however, this assessment was incomplete, as it considered only the high pressure abrasive 

blasting work, not the recoating of the penstock interior (Section 4.1.1). As a result, the fire potential due 

to the use of solvents within the confined space of the penstock was not evaluated. 

As an experienced contractor and the seventh-largest specialty paint company in 2005, RPI would be 

reasonably expected to understand the need for safety during relining operations in confined spaces

(Engineering News-Record, 2005). Indeed, documents from the RPI bid and safety program reveal that 

the company was aware of the potential hazards posed by the penstock itself and those created when 

performing spraying operations inside it. The RPI bid contained several references to prior projects where 

similar safety issues to that of the penstock were encountered, including limited access in confined spaces 

 

45 Although APPA is an industry association for public utilities, which Xcel is not, the good practice guidance 

APPA publishes is useful to both public and private utility groups. 
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that created ―inherent risks.‖ RPI stated in its bid submission to Xcel that it handled these risks by 

providing training; confined space watch personnel; and emergency equipment, such as breathing 

apparatus and extraction devices. Whether these safety actions were actually implemented in the prior 

projects is unclear; however, that RPI listed them as precautionary steps taken in previous projects speaks 

to the company‘s familiarity with managing the hazards. Yet, training was less than adequate (Section 

9.0), and no emergency breathing apparatuses were provided to the work crew at the penstock.

A KTA project engineer sent a review of RPI submittals46 for the penstock recoating project to the Xcel 

Reline Project Team Leader. The RPI coating application plan clearly states that the sprayer would be 

brought inside the penstock. The product-specific application procedures for the epoxy describe the short 

working time after the base and hardener are mixed and the need to flush the sprayer with a solvent before 

introducing the epoxy into the system and to clear any blockages as necessary in the spraying equipment 

during use. Based on his review, the KTA project engineer recommended including eight additions and 

clarifications to the contract between Xcel and RPI, three of which had safety implications.47 Yet the 

project engineer made no recommendations to Xcel concerning safeguards that would need to be 

employed if flammable solvents were used to flush the sprayer inside the penstock (such as ventilation 

and explosion-proof lights), nor did he provide recommendations for use of safer (e.g., nonflammable) 

solvents for flushing the sprayer. Xcel also had its own employees review the RPI bid submission 

documentation, but no actions were taken to manage the hazards associated with using flammables within 

a confined space.

 

46 KTA reviewed a number of RPI‘s bid documents, including a surface preparation and coating application plan, a 

project schedule, product-specific application procedures, and product data sheets for the two-part epoxy material.

47 The three additions that had potential safety implications were the need (1) for adequate heating inside the 

penstock, (2) to ensure the bulkheads were fitted with manways, and (3) to install strung lighting supplemented 

with spotlights.
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In the September 5, 2007, preconstruction meeting, Xcel and RPI management and safety personnel 

discussed the need for additional safety precautions for the recoating project. Handwritten notes on an 

agenda in the files of the Xcel safety director indicate that both a safety addendum to the contract (Section 

8.2.1) and the need to enforce Xcel‘s ―Stop Work Authority‖ policy during the recoating project were 

discussed. Additionally, the Xcel safety director‘s handwritten notes indicate his recognition of the need 

for an external rescue team during the penstock work. 

Months prior to the incident, the Xcel penstock recoat project leader emailed a power plant engineer and 

the Xcel plant manager stating that the contractors involved in the penstock work were requesting 

information concerning the site‘s confined space entry procedures, whether the air was being monitored, 

and who was responsible for the monitoring. The project leader received a reply email from the Xcel plant 

manager that this information would be covered in contractor orientation. This brief orientation –

consisting of a 30-60-minute checklist review of potential hazards – was held on three separate occasions, 

led by different Xcel personnel and attended by various members of the crew. During one of the sessions, 

the Xcel employee leading the orientation did learn that RPI would be using a ―ketone‖ solvent to clean 

the sprayer inside the penstock, but even after the incident he stated he was unaware if Xcel had received 

a copy of the solvent MSDS before epoxy application began. 

6.3 No Monitoring Plan Established

Neither Xcel nor RPI had a monitoring plan established for safe entry and work inside the penstock. The 

OSHA Permit-Required Confined Spaces Rule discusses appropriate procedures for atmospheric testing 

to include evaluating the atmospheric hazards of the permit space that may exist or arise so that both entry 

procedures and safe entry conditions are clearly stipulated in advance of conducting work [29 CFR 

1910.146] (Appendix B). Recommended practices for monitoring potential flammable atmospheres 

suggest that any company performing atmospheric monitoring should implement a ―written, established 

protocol that describes the sampling procedures, sampling locations, and required sample collection time‖ 

(Levine, 2004, pp.35). Because hazardous gases or vapors may be stratified within the atmosphere, the
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location of air monitoring can significantly impact a worker‘s ability to determine if a flammable 

atmosphere exists. Additionally, the sampling procedures should address if continuous atmospheric 

testing is necessary. Criteria for determining this need includes work spaces with the potential for changes 

in work activities that ―may affect the composition, concentration, flow rate or volume, pressure and/or 

temperature of flammable liquids, vapors or gases‖ or changes in ―ambient conditions such as 

temperature, wind direction and wind speed‖ (Levine, 2004, p.36). Both of these factors were present in 

the penstock recoating work environment the day of the incident. 

However, interviews with surviving RPI employees revealed that the atmosphere was not monitored 

continuously in the work area inside the penstock. Instead, readings were taken only two to three times 

per day at the penstock entrance by the RPI attendant, which did not meet the OSHA Permit-Required 

Confined Spaces Rule requirement for continuous monitoring of entry conditions in the areas where 

authorized entrants are working if the permit space is large, or part of a continuous system, and where 

isolating the space is infeasible [29 CFR 1910.146(d)(5)(i)]. While this monitoring requirement is related 

to the size of the space and not to the specific hazard of using a flammable solvent in the confined space, 

RPI was nonetheless required to continuously monitor the work area in the penstock.48

6.4 No Evaluation of Hazards When Conditions Changed

When work conditions inside the penstock changed from blasting to recoating, Xcel or RPI should have 

re-examined the space for new hazards, as per the OSHA Permit-Required Confined Spaces Rule.

49 As 

listed in 6.1.2, the CSB noted that RPI workers experienced a number of potential hazardous atmospheric 

 

48 Post-incident, OSHA issued a willful violation to RPI Coating ($63,000 proposed penalty) [OSHA, March 21, 

2008, inspection 310470034, citation 2(9)] and serious violations to both Xcel and KTA ($4,500 proposed 

penalties, each) [OSHA, March 21, 2008, inspection 310470059, citation 1(9) and inspection 310470083, citation 

1(6), respectively] for not continuously monitoring the air during the penstock recoating project. 

49 The Rule states: ―When there are changes in the use or configuration of a non-permit confined space that might 

increase the hazards to entrants, the employer shall reevaluate that space and, if necessary, reclassify it as a permitrequired confined space‖ [29 CFR 1910.146(c)(6)] and certify it through the required documentation [29 CFR 

1910.146(c)(7)(iii)].
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conditions within the penstock, including dust from abrasive blasting, flammable atmospheres from the 

use of solvents, welding fumes from hot work, and accumulation of toxic carbon monoxide from the use

of an ATV with an internal combustion engine. Each time one of these hazards was introduced or 

encountered in the confined space, the permit should have been updated to accurately reflect the hazard(s) 

and the appropriate safeguards to protect the entrants and ensure that acceptable entry conditions were 

maintained. But neither RPI nor Xcel reassessed the hazards as conditions changed, thus these hazards 

were unmanaged.

50

6.5 Safer Solvent Not Chosen

As the application procedures supplied to both Xcel and RPI made clear, the use of the sprayer inside the 

confined space required the use of a solvent to flush and clean the sprayer, which would occur in the open 

atmosphere of the penstock at least daily, given the project work schedule. Flammable MEK was chosen 

as the solvent for the penstock recoating project. 

Bringing a flammable into a confined space to use in the open atmosphere increases the likelihood of a 

potential fire because it adds the second of the three conditions required for combustion: fuel, oxygen, and 

an ignition source – oxygen was already present in the penstock. Fire risk is significantly heightened 

because ignition sources can be difficult to identify and control where flammable liquids are being used. 

These hazards were not adequately assessed when MEK was chosen as the penstock recoating project 

solvent.

6.5.1 The Hazards of MEK

MEK is an organic chemical compound often used as a solvent in painting and industrial recoating 

activities. MEK is listed by the National Institute for Safety and Health (NIOSH) as ―highly flammable‖ 

 

50 The CSB also noted that none of the forms were filled out completely and only portions of forms were retained for 

some dates. 
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(NIOSH, 1998). MEK is a Class IB Flammable Liquid, with a flash point below 73 °F (23 °C) and boiling 

point at or above 100 °F (38 °C) (NFPA 704, 2007b, Table 6.2; NIOSH, 1998).

As a highly flammable liquid, MEK poses significant hazards if used in a work area and the safety risk 

potential increases dramatically when the location of work is within a confined space. The epoxy 

application procedure specifically highlights the flammability risk involved with the use of MEK,51 as do 

the MSDSs Xcel and RPI provided to the CSB.52 ,53

As part of its investigation, the CSB conducted a brief review of available MSDSs on MEK and found a 

number of MSDSs with warnings that the product should not be used in confined spaces.54 The MEK 

MSDSs – including the MSDS Xcel provided to the CSB55– warn that MEK vapors may cause a flash 

fire or ignite explosively, and that the solvent‘s vapors may travel considerable distance to a source of 

ignition and flash back.56 The MSDSs instruct the user to ―prevent buildup of vapors or gases to explosive 

concentrations.‖57 The various MSDSs also warn that MEK is sensitive to static discharge, so containers 

of the solvent should be bonded and grounded for transfer to avoid static spark.58

 

51 The procedures states in capital bold letters that MSDSs should be consulted and ―proper fire and ventilation 

procedures should be followed. 

52 The MSDS provided by Xcel states, ―DANGER! EXTREMELY FLAMMABLE LIQUID AND VAPOR. 

VAPOR MAY CAUSE FLASH FIRE‖ (emphasis in original), and the MSDS RPI provided to the CSB also states 

that MEK is ―EXTREMELY FLAMMABLE...vapors will accumulate readily and may ignite explosively‖ 

(emphasis in original). 

53 According to RPI, this MSDS was sent via fax to the Cabin Creek site by the company post-incident; it was 

provided to the CSB upon subpoena request in July 2008. 

54 Carboclor MSDS on MEK, June 2008; Sunnyside Corporation MSDS on MEK, 1/12/06; RAW Chemical

Distribution Limited MSDS on MEK, 11/11/02; Linchem, Ltd. MSDS on MEK, 9/10/02.

55 Mallinckrodt Baker, Inc. MSDS on MEK, 8/17/05 (retrieved online by Xcel Energy on 10/12/07 from 

www.jtbaker.com/msds/englishhtml/M4628.htm).

56 Sunnyside Corp. MSDS on MEK, 1/12/06; RAW Chemical Distribution Limited MSDS on MEK, 11/11/02; 

Linchem, Ltd. MSDS on MEK, 9/10/02.

57 Sunnyside Corp. MSDS on MEK, 1/12/06; RAW Chemical Distribution Limited MSDS on MEK, 11/11/02.

58 Mallinckrodt Baker, Inc. MSDS on MEK, 8/17/05; Sherwin-Williams Co. MSDS on MEK, 10/2/07; Sunnyside 

Corporation MSDS on MEK, 1/12/06.
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Despite the warnings within the MSDSs about MEK‘s extreme flammability and RPI‘s own safety 

policies that require flammable liquids to be stored and handled in safety cans, 59 2- and 5-gallon (7.6 and 

19 liters) plastic buckets were used to transport and store MEK solvent in the penstock. One open 5-

gallon (19 liter) plastic bucket of MEK was placed under the solvent pump of the sprayer to supply 

solvent to the mixing block. After using MEK to clean out the spray wands, the 5-gallon (19 liters) plastic 

buckets of used solvent were left opened adjacent to the sprayer system instead of removed from the work 

area. Approximately 6 additional gallons (23 liters) of MEK were brought into the penstock in 2-gallon

(7.6 liter) plastic buckets specifically to flush and clean the sprayer system immediately prior to the 

incident. Additionally, the MEK solvent was transferred from a 55-gallon (208 liter) drum in the storage 

trailer, hand-carried into the penstock, and stored in plastic buckets around the work area; these buckets 

were reportedly not covered when inside the penstock prior to and during the solvent cleaning process.

6.5.1.1 Evidence that Xcel and RPI Knew that MEK would be Used

While Xcel has disputed its knowledge of the use of MEK in the penstock recoating project, from the 

totality of evidence – including the fact that the Xcel project scheduler stated he was made aware that RPI 

would be using a ―ketone‖ during the recoating work – the CSB has concluded that Xcel was aware of the 

use of flammable solvent in the penstock, and that both companies were aware that MEK solvent would 

be used during the epoxy application process.

Xcel sent all potential bidders for the penstock recoating project the document ―Surface Preparation and 

Repainting of Interior of the Cabin Creek Penstock‖ prepared by KTA and reviewed by a number of Xcel 

employees involved in the penstock project planning, which states that a solvent would be used within the 

 

59 RPI‘s ―Fire Protection and Prevention‖ policywithin its IIPP, as well as several others requires all flammable 

liquids to be stored and handled in safety cans. A safety can, as defined in the IIPP, is an approved container of not 

more than 5 gallons capacity, having a flash arresting screen, spring closing lid and spout cover.
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penstock for initial cleaning of the surface, and instructs the bidders on appropriate storage methods for 

solvents and thinners during the project. 

As part of its bid submission package to Xcel, RPI provided the three-page ―Surface Preparation and 

Application Guide‖ from the manufacturer of the two-part epoxy product, that also referenced the need 

for a solvent for cleaning purposes. During the bid evaluation and selection process, this contractual 

documentation was reviewed by numerous management and safety personnel from both companies. 

In August 2007, RPI‘s vice president provided the Xcel Cabin Creek project manager with the more 

detailed epoxy ―Specification and Application Procedures,‖ which discusses the use of solvents in the 

recoating process several times.

60

Once RPI was onsite, evidence of the planned use of MEK within the penstock was witnessed by workers 

and supervisors from both companies. On September 12, 2007, 110 gallons (416 liters) of MEK [two 55-

gallon (208 liters) drums] was delivered to the Cabin Creek site and signed for by an RPI crew member. 

According to testimony of the crew, the Xcel principle engineer and project scheduler witnessed the 

delivery of the MEK and confirmed with the crew that it was the solvent being delivered. 

That same day, RPI conducted a test spray with the epoxy products and solvent on the Xcel Cabin Creek 

site. Five gallons of MEK were purchased for the test spray and used afterward to clean the equipment. 

The Xcel principle engineer was present during these activities and signed off on the invoice for the 

solvent and epoxy. 

 

60 The procedure document instructs that, upon initial setup, ―solvent should be flushed through the line to check for 

any foreign matter, leakages, or blockages.‖ These procedures state that if blockages or other stoppages occur, 

―immediately shut off the heater, and place a clean bucket of solvent underneath the pump and flush the lines.‖ It 

goes on to state that merely spraying the material will build pressure and cause the epoxy product to begin to set; 

as a result, the user is instructed to ―flush solvent through the system‖ and ―re-circulate solvent until the pump and 

lines are clear.‖ Finally, the procedures provide guidance about cleanup: ―Any mixing and application tools should 

be immediately wiped or scraped clean. Any residue can be removed with a solvent, such as 1,1,1-trichloroethane, 

MEK or an appropriate blend.‖
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6.5.2 Safer Alternatives

None of the companies considered safer alternatives to the flammable MEK, nor did they identify work 

tasks involving the solvent that could have been performed outside the penstock.

One significantly less hazardous option is a citrus-based solvent, a variety of which are available for 

industrial purposes and are often biodegradable, non-toxic, and have significantly higher flash-points than 

flammable solvents like MEK.61 ANSI Z117.1, ―Safety Requirements for Confined Spaces‖ recommends

that the hierarchy of controls be followed to address confined space hazards [ANSI Z117, 2009, p.17]. 

Using this method of hazard control, primary consideration is given to eliminating the hazard or using 

engineering controls such as substitution; for instance, using less hazardous, non-flammable substitute 

solvents for the highly flammable MEK.

Another more effective safety approach within the hierarchy of controls would have been to conduct the 

work outside the confined space.62 In the Cabin Creek penstock incident, while the hoses from the mixing 

block to the spray wands required immediate flushing due to the mixing the two-part epoxy, the sprayer 

itself did not need to be cleaned inside the confined space. 

6.6 Xcel’s and RPI’s Confined Space Policies

Xcel‘s and RPI‘s corporate confined space policies in effect prior to the incident did not effectively 

establish safe limits for flammable atmospheres that would prohibit entry or occupancy when the limits 

were exceeded. Xcel‘s corporate confined space policies did not effectively establish acceptable entry 

conditions for flammable atmospheres as a specific percentage of the LEL, nor did they provide explicit 

 

61 A less flammable, but still hazardous, option is 1,1,1-trichloroethane. This organic compound has a history of use 

as a solvent within the industrial painting industry; however, its use has lessened due to its toxicity. The 

manufacturer of the two-part epoxy used in the penstock recoating project has communicated that several nonflammable solvents would be effective for cleanup activities, including n-Propyl Bromide and citrus-based 

products. 

62 The United Kingdom Confined Spaces Regulation [Statutory Instrument 1997, No. 1713] imposes the duty of first 

avoiding entry into the confined space by conducting the work outside the space, unless entry is unavoidable.
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warnings to prohibit entry or occupancy based upon a specified flammable atmosphere limit. Xcel‘s 

confined space permit form allowed entry even when ―atmospheric and/or serious hazards in the space 

that cannot be controlled or eliminated‖ were present, if certain unspecified precautions were being 

implemented. The confined space entry policy in effect at the time of the incident of Northern States 

Power Company, a subsidiary of Xcel, however, provides effective specific entry and occupancy limits 

for flammable atmospheres. The policy establishes 10 percent of the LEL as an alarm point and states: 

―If the air monitor alarms all entrants shall immediately evacuate the space.‖ After the Cabin Creek 

incident, Xcel revised its confined space policy with improvements that designated greater than 10 

percent of the LEL as an ―alarm limit.‖ However, the new policy does not explicitly prohibit entry or 

occupancy based upon the alarm limit, unlike the Northern States‘ policy.

RPI‘s confined space entry policy and permit provided to Xcel as part of the contractor selection process 

did not provide for safe entry and occupancy limits or effectively prohibit entry when those limits were 

exceeded. Neither the policy nor the permit defined a hazardous atmosphere or provided for acceptable 

confined space entry conditions. 

The failure of Xcel‘s and RPI‘s confined space policies to establish safe flammable limits undermines the 

importance of monitoring in permit-required confined spaces; the need for periodic or continuous 

monitoring will not be effectively communicated to managers and workers if no limits are specified. This 

safety gap can also lead to a failure to address the serious hazards of flammable atmospheres, as was the 

case in the Cabin Creek penstock.
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7.0 Emergency Response and Rescue

The CSB determined that the flash fire inside the penstock occurred at approximately 1:55 p.m. and the 9-

1-1 call was placed at 2:03 p.m.. While the initial emergency responders arrived at the Cabin Creek site in 

less than 10 minutes from the dispatch notification, the first community emergency responder capable of 

performing a confined space rescue operation, West Metro Fire Rescue, did not enter the property for 

more than an hour and a half after the fire started due to their distant location. The trapped workers likely 

succumbed to smoke inhalation about one hour prior to West Metro‘s arrival. An immediately available 

qualified confined space technical rescue provider likely would have been able to effectively control the 

fire and prevent the worker fatalities. However, no such rescuers were immediately available outside the

penstock on the day of the incident.

The lack of competent technical rescue services at Cabin Creek was the result of: 

Xcel‘s and RPI‘s lack of a competency evaluation of available confined spaces rescue services, as 

required by the OSHA Permit-Required Confined Spaces Rule;

The failure of Xcel and RPI to identify the life-threatening hazards of using flammable solvents 

in the penstock and arrange for immediately available emergency response services onsite prior to 

the start of the epoxy application.

As a result of not evaluating the competency of available emergency service providers to perform permitrequired confined space rescue, nor arranging for emergency response support to be onsite prior to the 

start of the penstock work activities, neither Xcel nor RPI were prepared to handle a confined spaces 

emergency such as they experienced on October 2, 2007. And because the first responders to the incident 

were voluntary firefighters without the training or qualifications to peform permit-required confined space 

rescue, no one was immediately available and capable to successfully enter the penstock to rescue the 

trapped workers. The CSB also notes that alternative egress and/or safety chambers were not provided in 
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the penstock and the State of Colorado lacked a training and certification program for technical rescuers 

including confined space technical rescue.

7.1 Lack of Preparation by Xcel and RPI to Ensure Availability of 

Qualified Rescue Personnel

The OSHA Permit-Required Confined Spaces Rule [29 CFR 1910.146(k)] requires the employer to either 

arrange for a competent outside rescue and emergency services provider, or ensure that its employees can 

perform rescue and emergency services competently when they are working within a permit-required 

confined space. However, RPI and Xcel did neither. 

The emergency response and rescue preparation conducted by Xcel and RPI ineffectively consisted of 

instructing RPI personnel that, in the event of an emergency inside the penstock, 9-1-1 would be called by 

Xcel personnel. On October 2, 2007, this was the emergency response step taken. Unfortunately, the first 

and closest emergency responders arriving at the Cabin Creek site were not prepared for entry into the 

penstock‘s confined space. Approximately less than 10 minutes after the 9-1-1 call, the first community 

emergency responder to arrive onsite was the Clear Creek County Sheriff‘s office, who established the 

Incident Command. Several volunteer Clear Creek County Fire Authority (CCFA) emergency medical 

and firefighters arrived next, but none of these responders had the necessary equipment or training to 

extinguish the fire in the penstock or initiate a rescue of the trapped RPI personnel.63 Additionally, the fire 

service organizations had no pre-knowledge of the hazards of the chemicals onsite, their quantities, or 

locations. The site was not pre-equiped with appropriate firefighting equipment specific to the unique 

hazards of the penstock. Such planning and communication should have been implemented with

designated emergency responders in advance of any recoating work being conducted withtin the penstock.

 

63 This was noted by the Xcel control room operator, who added the following entry in the control room logbook: 

―14:20 Emergency services w/out confined space fire training – they have summoned a Denver team.‖
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When an employer chooses to rely on an outside rescue and emergency service, the OSHA Confined 

Spaces Rule requires the employer to evaluate the service‘s ability, in terms of proficiency with rescuerelated tasks and equipment, to function appropriately while rescuing entrants from the particular permit 

space or types of permit spaces identified [29 CFR 1910.146(k)(1)(ii)]. However, neither Xcel nor RPI 

evaluated CCFA‘s or other nearby responders technical capabilities. 

Had Xcel and RPI arranged for a competent outside rescue and emergency services provider prior to 

beginning work inside the penstock and supplied the provider with pertinent information about the 

chemicals being used within the confined space, the first responders to the incident would likely have 

been prepared for entry, firefighting, and rescue activities.

7.2 Failure by Xcel and RPI to Arrange for Timely Rescue

Local fire service officials told the CSB that any attempted rescue of the trapped RPI workers could have 

been successful only with sufficient numbers of responders and the appropriate equipment immediately 

available onsite to fight a fire that was more than 1,450 feet (442 meters) inside the penstock.

The OSHA Permit-Required Confined Spaces Rule requires that emergency response be timely, based on 

the specific hazards involved in the entry. According to a December 9, 2003, settlement agreement 

between OSHA and the American Petroleum Institute (API), a ―timely‖ response to a confined space 

emergency depends on the hazards the entrants may face. If entrants encounter hazards that are deemed 

potentially Immediately Dangerous to Life and Health (IDLH),

64 a rescue team must be stationed outside 

the confined space and ready for immediate entry. The use of MEK inside the penstock created the 

 

64 IDLH or Immediately Dangerous to Life or Health, is a personal exposure limit for a chemical substance set forth 

by the National Institute of Occupational Safety and Health (NIOSH); it is typically expressed in parts per million 

(ppm). OSHA‘s Permit-Required Confined Spaces rule for general industry states that IDLH ―means any condition 

that poses an immediate or delayed threat to life or that would cause irreversible adverse health effects or that 

would interfere with an individuals ability to escape unaided from a permit space‖ [29 CFR 1910.146(b)].
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potential for a flammable atmosphere and life-threatening conditions in the event of an ignition, 

especially when coupled with a single exit for evacuation. 

An immediately available rescue and response team is especially important for a worksite like Cabin 

Creek, which is situated in a remote mountainous location where timely response would be extremely 

difficult.

Depending on the road conditions, vehicle type, and speed, driving the 5.5 miles (8.9 kilometers) from the 

Georgetown fire station – the closest community emergency response facility – to the Cabin Creek 

hydroelectric plant takes between 10 and 30 minutes. At the time of the incident, the only improved road 

to the site, Guanella Pass, was steep, narrow, and winding (Figure 11). This road had no guardrails, was 

partially unpaved with loose gravel and potholes, and has many hairpin turns that made it hazardous to 

drive at speeds above 20 miles an hour (32 kilometers per hour).

65

 

65 CCFA personnel told the CSB investigators that the turns were so tight that one of their fire support vehicles had 

to completely stop and back up several times to navigate through the turns. 
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Figure 11. The winding, steep and narrow road from Georgetown to the Xcel hydroelectric plant

7.2.1 Requirements and Recommendations for Alternate Escape Routes or 

Safety Chambers 

While the need for immediately available qualified technical rescue services was critical given the 

hazards in the penstock, another safety precaution that should have been taken by Xcel and RPI was to 

plan for an alternative escape route out of the penstock or a safety chamber within it. However, there was 

no plan for an alternate escape route out of the penstock if the primary route were to be blocked in an 

emergency.66

The penstock is a 4,163-foot (1269-meter) long sloping, underground confined space that required an 

access door in the side of the penstock to be cut for the recoating work crew to enter; this access opening 

 

66 Bid documents indicate that one of the unsuccessful bidders contemplated building a stairway to an egress 

opening in the mushroom.
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was effectively the only way in or out of the penstock for RPI workers. Once the penstock starts its 55

degree incline, it is physically impossible to traverse the penstock without climbing paraphernalia setup in 

advance from the mushroom67 and individual skill and qualifications in rigging and rope climbing, which 

none of the contractors were prepared or trained to do from inside the penstock. All of the deceased RPI 

workers were found beyond the west bulkhead with most near the start of the 55 degree incline.

The need for secondary escape routes from penstocks is identified in the American Society of Civil 

Engineering (ASCE) Task Committee‘s ―Guidelines for Inspection and Monitoring of In-Service 

Penstocks‖ (ASCE, 1998, Section 2.3.6.1).

Alternatively, a safety/rescue chamber68 inside the penstock could have housed fresh air, water, and 

reliable communication equipment for the trapped workers. The CSB notes that a useful guidance 

document was published in 2009 by the National Institute for Occupational Safety and Health (NIOSH) 

addressing instructional materials on refuge chamber setup, use, and maintenance (2009). At a minimum, 

self-contained breathing apparatuses could have been placed west of the west bulkhead, so that potentially 

trapped workers would have access to fresh air until rescue could be performed.69

Addressing the lack of secondary egress hazard by creating an alternative/emergency exit or installing a 

rescue chamber,

70 and staging qualified emergency rescuers near the penstock entrance would have likely

have prevented the fatalities in this incident. 

 

67 In September 2007, Xcel employees used climbing equipment to enter the penstock from the mushroom‘s vertical 

shaft entrance to inspect the interior for potential wear and damage of the concrete portion of the penstock. 

68 A safety/rescue chamber is an airtight chamber stocked with food, water, and oxygen, and typically used in 

underground mines. Such a chamber recently saved 72 miners who were trapped underground for 30 hours at the 

Mosaic Potash Mine in Saskatchewan, Canada.

69 Three people survived a Bunker, Missouri, mine fire in January 2010 although their escape route was blocked by 

burning equipment; the mine had a rescue chamber with compressed air supplies that kept them alive until rescue 

teams were able to save them six-and-a-half hours later. 

70 This list also is not intended to be all inclusive, as other solutions could include actions such as increasing the 

ventilation and installing fire suppression.
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7.3 Lack of a Technical/Confined Space Rescue Certification 

Progarm for Volunteer Firefighters

The first responders to the Cabin Creek penstock fire were local voluntary firefighters from the CCFA; 

none of these individuals held technical rescue qualifications or had received up-to-date workplace 

confined space training. The significant hazards inherent with confined spaces require specialized training 

and certification.

The Colorado Department of Public Safety, Division of Fire Safety, administers the firefighter voluntary 

certification program [8 CCR 1507] in the state. The purpose of this program is to measure the level of 

knowledge, skills, and abilities of firefighters and to attest that they meet nationally recognized standards. 

At the time of the incident, the state had certifications for various levels of firefighters and fire officials, 

fire inspectors, fire instructors, hazardous materials responders, fire apparatus drivers, and emergency 

medical first responders, but no certification program for technical and/or confined space rescue. 

Interviews with Division of Fire Safety personnel revealed that the state does not track how many 

firefighters in the state are trained or certified in technical rescue because there is no certification program 

for this specialty. Interviews with various state fire officials revealed that several fire service and response 

organizations have achieved the operational capacity to conduct technical rescue, including confined 

space rescue71; however, only a small number of Colorado firefighters have been individually certified to 

perform technical rescue.72

 

71 NFPA 1670: Standard on Operations and Training for Technical Search and Rescue Incidents (2009) issued by the 

National Fire Protection Association (NFPA), establishes levels of functional capability for conducting technical 

rescue operations. Several Colorado fire service and responder organizations have been deemed to have 

established functional capability under this standard, including organizations affiliated with the Colorado Urban 

Rescue Task Force. NFPA 1670 does not, however, address individual technical rescuer qualifications. 

72 NFPA 1006: Technical Rescuer Professional Qualification (2008) establishes job performance requirements for 

rescue technicians.
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At the time of the penstock incident, only two entities in the region were identified to have the 

organizational experience and training to handle the technical rescue issues this incident presented: West 

Metro Fire Rescue,73 located in Denver (45 miles or 72 kilometers, approximately 1 hour 15 minutes 

travel time); and the Henderson Mine,74 located near Empire, Colorado (21 miles or 34 kilometers, 

approximately 35 minutes travel time). The CCFA contacted and requested both to support the incident; 

due to the time each required to assemble a rescue team and travel to the Cabin Creek site, neither arrived 

at the penstock until approximately an hour after the trapped workers succumbed to smoke inhalation.

State fire officials informed the CSB that the availability of state voluntary certification for technical 

rescue, including confined space rescue, would improve the capabilities and capacity of Colorado fire 

service personnel to respond to events similar to the Cabin Creek incident.

 

73 Members of the West Metro Fire Rescue have been trained in technical rescue in confined spaces as part of their 

duties as members of a regional FEMA Urban Search and Rescue Team, but were unfamiliar with the 

configuration of the Cabin Creek penstock

74 Although the rescue team at the Henderson Mine is not trained in confined space rescue, the team has specialized 

training in underground mine rescue. As the penstock was bored through solid granite, it has many of the same 

characteristics and hazards as an underground mine. This rescue team is a private entity and not a public 

emergency response organization. 
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8.0 Contractor Selection and Oversight

Having both a strong contractor selection methodology and contractor oversight policy ensures that the 

owner receives both quality work from its contractors and worker safety is maintained for its own 

employees and those of the contractor. However, neither the methodology nor the oversight Xcel 

employed for the Cabin Creek penstock project adequately ensured that the recoating work would be 

conducted safely.

8.1 Contractor Selection

Xcel‘s contractor selection methodology did not disqualify contractors with substandard safety records 

from bidding on the penstock project. 

8.1.1 Contractor Selection Process for the Penstock Project Request for 

Proposal 

In April 2007, Xcel initiated the competitive bidding process to select a coating contractor for the Cabin 

Creek penstock recoating project. The company issued an RFP 75 to several contractors who were to be 

selected based upon the ―best value/best overall evaluated offer‖76 rather than price alone. The Xcel RFP 

stated that the contractor would be evaluated, scored, and chosen using weighted rating factors, such as 

pricing (15%), safety experience modification rate (EMR)77 (5%), historical quality of services and 

equipment (10%), operating history (10%), completeness of proposal (5%), and key personnel experience 

 

75 Xcel used the RFP procurement method for selecting suppliers of goods and services in more substantial 

acquisitions or projects.

76 The ―best value‖ procurement method considers a variety of factors in selecting contractors in addition to price, 

such as experience with similar projects, on-time completion, employee training, and safety record (TRB, 2006, 

p.S-3). 

77 EMR is used by the U.S. insurance industry ―to determine premiums for workers‘ compensation insurance. An 

EMR less than 1 indicates above-average injury and illness performance, and an EMR greater than 1 indicates 

below-average performance. An owner can get some indication of a contractor‘s past safety performance by 

reviewing the contractor‘s EMR. A comparison of the EMRs of contractors bidding on a project may improve the 

selection process‖ (API RP 2220, 2005a, p.13). The RFP called for reporting the interstate EMR.
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and continued availability (5%).78 The RFP also established minimum qualifications and experience, 

including the need for at least five years of successful similar recoating experience and a QP 1

certification from the Society for Protective Coatings (SSPC), an industrial protective coatings trade 

association. 79 The Xcel contractor selection process for larger projects, such as the Cabin Creek penstock 

recoat, also included a prequalification80 step that examined the contractor‘s financial capacity to 

successfully perform the work; however, the prequalification step did not consider safety performance.

Xcel‘s first attempt to select a contractor was unsuccessful. Of the three bidders submitting proposals, 

only one bid, from Certified Coatings Company (CCC), was evaluated as technically and commercially 

complete; however, its proposal was $450,000 above the budgetary allotment. Rather than increase the 

capital budget, Xcel re-bid the penstock project to find additional interested contractors. In late July 2007, 

an Xcel team that included the Cabin Creek plant manager and the penstock recoat project manager 

evaluated and scored the second group of proposals from four bidders. 

 

78 Other rating factors were exceptions to terms and conditions (10%), compliance with performance guarantees 

(15%), technical exceptions (5%), creative proposal options (10%), and QP 1 Certification/Experience (10%). 

79 SSPC certifies coating contractors based on demonstrated competence in areas such as technical capabilities, 

safety and environmental compliance, quality control, and management procedures. The certification process 

requires an evaluation of submittals to SSPC and an onsite audit of an active job site to verify that the stated 

programs are implemented. SSPC has established a QP 1 disciplinary action system with criterion for issuing 

warnings and placing contractors on probation or suspension based upon the severity of critical faults or violations

in the areas of competence. (SSPC, http://www.sspc.org/certification/PCCP/QP1main.html , 

http://www.sspc.org/certification/PCCP/DAC.html, accessed March 8, 2009.)

80 Contractor selection processes often have an initial prequalification during which each potential contractor must 

meet basic qualifications, including safety. A prequalification process is typically pass/fail; owners evaluate 

contractors and craft workers to determine if they meet the identified criteria and only firms that meet or exceed 

those requirements are allowed to bid in the final selection process. In this case, Xcel‘s prequalification process 

considered only the financial capacity of the potential contractor.
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8.1.2 RPI Safety Record “Not Acceptable,” but Allowed to Bid

The top two evaluated proposals from the second round of bidding were from CCC and RPI.

81 Xcel‘s

project manager summarized the results of the proposal evaluations stating ―from a technical and quality 

perspective, Certified Coatings (CCC) is the best evaluated proposal. They are at least $500 k over 

budget. The second best evaluated proposal is Robinson-Prezioso (RPI). Their safety EMR is high[,]

although their OSHA incident rate does not reflect a safety problem. Their proposal is very close to 

budgetary requirements.‖ The KTA consultant assisting Xcel stated that RPI‘s high EMR may have been 

the result of fatalities from their work on the ―recent Golden Gate bridge project.‖82 The RPI EMR was 

trending upward from 1.03 in 2005 to 1.28 in 2006; the contractor evaluation team was aware that under 

Xcel‘s policies, an EMR rate of 1.0 or above was unacceptable. In fact, the Xcel team gave RPI‘s 

proposal a safety rating of ―zero‖ in the evaluation process. The RFP evaluation form the team used 

states that the rating of zero signifies that the bidder‘s proposal for that rating criterion ―does not meet 

minimum requirements [and means] automatic rejection.‖83

RPI‘s penstock recoating proposal, however, was not rejected. The Cabin Creek plant manager concurred 

with the project manager: ―I agree with you that RPI be the one selected due to cost and the fact that they 

are qualified.‖ He recommended that the Xcel Colorado safety supervisor evaluate RPI‘s safety record 

and contact the contractor to discuss its EMR number. The project team asked the safety supervisor to 

investigate ―whether a pattern of negligence is evident for this company [RPI].‖ When the Xcel safety 

 

81 RPI‘s total score of the weighted rating elements was 4.3 with a technical ranking of 2.9; CCC‘s total score was 

4.25 with a technical ranking of 2.95. RPI‘s bid was slightly over $1.3 million and CCC‘s was $1.7 million, a 

difference of less than $400,000. 

82 RPI had two fatality incidents during the Golden Gate retrofitting project. In September 2001, a passing motorist 

was killed by a falling scaffold. Then, in January 2002, an employee was crushed and four co-workers were 

injured when a platform buckled as it was being lowered onto a truck (Bjelland, S., et al., 11 Oct 2007).

83 The Cabin Creek recoating proposals were rated with a scoring system that ranged from 0-5, with ―0‖ representing 

the lowest score and defined on the scoring sheet as ―does not meet minimum requirements, automatic rejection.‖ 

The rating score of ―5‖ was defined as ―exceeds all requirements.‖
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supervisor inquired, the RPI safety director stated that the company‘s EMR was high due to the Golden 

Gate Bridge job and that the company‘s EMR was trending down in 2007.84

8.1.3 Contractor Selection and Safety: Historical Background

An influential Business Roundtable report published in 1982, ―Improving Construction Safety 

Performance,‖ found that construction was one of the ―most hazardous occupations‖ in the U.S. with a 54 

percent higher injury and fatality rate based upon data from that period.85 The report determined that 

contractors with a history of positive safety performance are more likely to perform safely in the future 

than those with a poor safety record. The report recommends that safety be considered when selecting 

construction contractors and that factors such as past safety performance and present safety capabilities be 

evaluated. The report includes a model safety prequalification form for use in selecting contractors.

A 2008 comprehensive report on contractor safety prequalification, ―Contractor Safety Prequalification,‖

(Phillips and Waitzman, 2008) refers to a 1991 John Gray Institute report, ―Managing Workplace Safety 

and Health: the Case of Contract Labor in the U.S. Petrochemical Industry,‖ as a ―bellwether‖ for 

subsequent industry interventions addressing contractor safety, including the issue of contractor safety 

 

84 This information is not completely accurate. OSHA‘s ―300 Log of Work-Related Injuries and Illnesses for 2006,‖ 

the year that RPI experienced an EMR of 1.28, listed no injuries or illnesses that occurred in the area of the Golden 

Gate Bridge or the Bay Bridge in California. Robison-Prezioso, Inc. was cited by OSHA for a fatality incident on 

a Bay Bridge on January 4, 2002, and another fatality incident on the Bay Bridge on September 25, 2001, where a 

motorist was killed. Both of these cases are still listed as ―open‖ on the OSHA website. The reference to the 

―Golden Gate Bridge‖ and RPI‘s high EMR rate was made by the Colorado Safety Supervisor in the Safety 

Addendum to the penstock contract signed by both parties. 

http://www.osha.gov/pls/imis/establishment.inspection_detail?id=300890555 , 

http://www.osha.gov/pls/imis/establishment.inspection_detail?id=300890100 , accessed June 4, 2009.

85 The Business Roundtable represents the CEOs of some of the largest corporations in the U.S. The association 

develops policy and advocates positions on diverse issues such as workforce development, sustainable growth, and 

corporate leadership. CURT is an independent offshoot of the Construction Committee of the Business Roundtable 

and represents the viewpoints of member construction owners seeking to improve construction industry practices 

including safety performance [CURT, 1990].
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prequalification.86 The report found an association between rigorous screening in the selection of 

contractors and positive safety performance (Phillips and Waitzman, 2008, pp.49-50).87

8.1.4 Contractor Selection and Safety: Current Industry Guidelines

Recent studies note a modern trend of alternative procurement methodologies that use factors other than 

low price to select construction contractors, such as quality, past performance, and safety88 (TRB, 2006, 

pp.40). Several organizations and industry associations, including the Construction Users Roundtable 

(CURT),89 the American National Standards Institute (ANSI), the American Industrial Hygene 

Association (AIHA), and FM Global, have developed guidelines and recommended practices addressing 

the use of safety criteria for selecting contractors. One common method is prequalification, typically a 

pass/fail system that ensures that only contractors who meet specific requirements, including safety, are 

allowed to compete (CURT, 2004, pp. 1, 5). Another common alternative construction procurement 

 

86 While the John Gray Institute report addresses contractor safety issues in the petrochemical industry, recent 

reports note the applicability of the conclusions from the 1991 report to general industry construction safety 

(Phillips and Waitzman,2008, pp.49-50). A case study examining the protection of contract workers at the 

Department of Energy‘s facilities found the John Gray Institute report to be the ―most comprehensive study of 

safety related to contract labor‖ (Gochfeld and Mohr, 2007, pp.1607-1613). 

87 In 1989, an explosion and fire at the Phillips Chemical Complex in Pasadena, Texas, killed 23 and injured 232 

workers. In the wake of the Phillips‘ incident, OSHA released a report to the President of the United States that 

identified multiple safety system failures that led to the incident including contractor safety issues (1990, pp.25-

26). As a result, OSHA commissioned a major study to examine the health and safety issues related to the use of 

contractors in the U.S. petrochemical industry. OSHA specifically directed that the study examine the ―the role of 

safety and health in the selection of contractors‖ (1990, p.64). Consequently, the John Gray Institute report used 

industry national surveys and case studies to understand the extent to which safety performance was considered in 

the selection of contractors (2006, pp.85-91). Partly in response to the John Gray report, OSHA‘s contractor safety 

requirements in the Process Safety Management Standard, C.F.R. 1910.119, include a requirement that employers 

when selecting a contractor ―shall obtain and evaluate information regarding the contract employer‘s safety 

performance and programs,‖ 1910.119(h)(2)(ii).

88 The TRB (Transportation Research Board) report addresses highway procurement; however, the discussion of 

procurement methodologies more generally references industry or public sector procurement trends.

89 CURT is an industry organization that promotes advocacy by users of construction services on national issues that 

includes ―developing industry standards and owner expectations with respect to safety, training and worker 

qualifications‖ http://www.curt.org/2_0_about_curt.html, accessed 10/27/09. CURT is composed of 66 member 

companies, organizations, and government entities that represent some of the largest industrial corporations and 

users of construction services in the U.S. including DuPont, ExxonMobil, Dow Chemical, Intel, Proctor & 

Gamble, Duke Energy, General Motors, Shell, the U.S. General Services Administrations, and the U.S. Army 

Corp of Engineers.
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method is referred to as ―best value‖ contracting where, in addition to price, other key factors such as 

safety can be considered in evaluating the bid package—this method typically involves a rating system 

where bidders are scored and the highest evaluated bidder is selected (TRB, 2006, pp. S-2 – S-8). A third 

common procurement method combines prequalification and best value practices: only prequalified 

bidders are allowed to compete in the final selection process and the evaluation and rating of the bidders 

is based on best value parameters (CURT, 2005, pp.6-9; TRB, 2006, p.1). Xcel used both prequalification 

and best value components in its selection of the Cabin Creek penstock recoating contractor. 

Industry guidelines addressing contractor selection support using a prequalification process that includes 

safety criteria. CURT has developed user practices addressing safety and contractor selection that are 

intended to educate CURT members and industry. The CURT User Practice, ―Construction Safety: The 

Owner‘s Role,‖ states that ―[c]ontractors must be prequalified by the owner to participate in the final 

contractor selection process. Demonstrated safety performance is a critical criterion used in the 

prequalification process‖ (CURT, 2004b, p.6). CURT guidance lists a variety of typical criteria for safety 

prequalification: staff qualifications, accident history, EMR, a contractor‘s safety program, and an 

owner‘s previous experience.90 Safety guidelines published by the AIHA, ―Health and Safety 

Requirements in Construction Contract Documents‖ identify a number of specific prequalification criteria 

including EMR, OSHA injury and illness logs, OSHA citations, and training certifications. ANSI 

Standard Z-10, ―Occupational Health and Safety Management Systems‖ also recommends that the 

 

90 The CSB noted in its BP Texas City investigation report (2007) that particular attention must be given by 

companies in developing effective safety performance metrics, which should include leading and lagging 

indicators (pp.184-185). Additionally, performance metrics that are commonly utilized may be inappropriate in 

some circumstances. For example, one contractor safety standard noted that the use of EMRs may not always be 

effective (API Standard 2220, 2005a, p.13). 
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contractor prequalification process include consideration of safety criteria for successful contractor safety 

performance management91 (ANSI/AIHA Z-10, 2005, p.20).

8.1.5 Xcel Corporate Policies on Contractor Selection

Xcel had corporate policies in place prior to the incident that addressed contractor safety and the role of 

safety in selecting contractors. However, while these policies allowed a prequalification process to be 

used, and a rating and ranking RFP competitive bid process that awarded the contract to the ―lowest 

evaluated bidder,‖ using a prequalification process was not mandatory and the minimum specified 

requirements were left to the procurement representative. Thus, the use of safety criteria in the 

prequalification process was not required, nor was it considered in the prequalification step at the Cabin 

Creek project.

In addition to the score of zero that RPI received, the Xcel evaluation team was also aware of RPI‘s 

accident history that involved fatalities. Had Xcel examined RPI‘s OSHA inspection database and other 

sources publically available, they would have discovered a lengthy history of serious OSHA citations, 

including a number of violations specifically involving the unsafe handling of flammable liquids

(Appendix B). Although the terms of the RFP relied on contractors to self-report accident histories, RPI 

did not provide Xcel with records related to several other serious relevant regulatory actions. 92, 93

 

91 API Recommended Practice (RP) 2221, ―Contractor and Owner Safety Program Implementation‖ also 

recommends contractor prequalification using a variety of safety criteria. The recommended practice states that 

―[t]he selection of a qualified contractor is the first step toward obtaining safe contractor performance‖ (API RP 

2221, 2005b). API‘s RP 2221 provides a comprehensive prequalification form that includes 48 questions and data 

requests. While the API publication addresses refining and petrochemical industry facility owners, it is persuasive 

guidance for general industry to improve contractor safety performance, particularly in performing hazardous 

repair, maintenance, and construction as in the Xcel penstock recoating project. 

92 In 2006 RPI agreed to pay a penalty of $145,000 to a division of the California Environmental Protection Agency 

to settle violations that included illegally disposing of hazardous waste and making false statements to government 

officials.

93 Xcel‘s ―Contractor Safety, Health and Environmental Questionnaire,‖ attached to the Cabin Creek penstock 

recoating RFP, required submission of any citations received from a regulatory agency during the past three years. 

RPI did not disclose to OSHA a 2005 serious OSHA violation in Arizona that occurred within the 3-year time 

period. 
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Moreover, Xcel‘s policies addressing contractor selection do not require that the records be verified and, 

in fact, Xcel confirmed to the CSB that it had not verified RPI‘s submissions or researched its 

background. 

Xcel‘s ―Contractor Safety‖ corporate policy provided for a health and safety evaluation of the contractor 

bids and recommended a review of the contractor‘s EMR. The policy stated that an EMR above 1 ―would 

normally be considered unacceptable for the construction industry,‖ but did not explicitly require a 

rejection of a bid proposal based upon the EMR. Xcel‘s policies allowed a contractor with ―unacceptable‖ 

safety performance to further compete in the contractor selection process. CURT guidance on contractor 

selection prequalification illustrates an approach that more effectively ensures safety:

Any contractors that do not meet base criteria fail and are not included on the potential list. An 

example of this type of pass/fail criteria might be: only contractors with an Experience 

Modification Rate less than 1.0 are acceptable (CURT, 2004a, p.5).

A prequalification policy consistent with industry guidelines would have disqualified RPI and prevented 

the firm from being considered in the final selection process.

8.2 Contractor Oversight

Xcel did not provide sufficient oversight to ensure that safe practices were upheld during the hazardous 

recoating work within the penstock.

8.2.1 Safety Addendum Added to Contract

In response to negative information about RPI‘s safety record, the Xcel safety supervisor proposed 

additional safety requirements for the penstock project. The agreement between Xcel and RPI included a 

safety addendum that required a number of additional safety measures. It reads as follows:
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1. RPI will be extra diligent toward safety, ensuring [that] they are carefully 

following their safety policies and procedures.94

2. RPI will respond to safety questions and concerns from Xcel Supply in a timely 

manner.

3. Xcel Supply will observe closely the work and report any concerns immediately 

to RPI‘s on site supervision (daily by on site personnel and randomly by Energy 

Safety).

4. Xcel Supply will provide our Stop Work Policy to RPI and that all understand 

that any Xcel Supply employee can stop a job. This is routine and covered in our 

contractor orientation at the start of all jobs.

Xcel concluded that if it kept a ―close watch‖ on RPI, the penstock recoating project would be safe and 

successful. 

8.2.2 Xcel Cabin Creek Site Contractor Oversight Activities and RPI Safety 

Performance

Xcel did not increase its oversight of RPI nor did it implement corrective actions even though, during the 

penstock recoating project site activities prior to the incident, Xcel managers had identified serious safety 

hazards associated with the work and were aware of several significant safety problems attributable to 

RPI:

An RPI worker slipped and fell inside the penstock due to the wet, slippery interior surface 

conditions. The worker suffered a dislocated shoulder and was treated at the hospital. 

The penstock was evacuated on several occasions prior to the incident due to high readings of 

CO, a toxic gas. 

 

94 RPI provided its entire ―Injury and Illness Prevention Program‖ safety manual to Xcel as part of its bid package 

submission; therefore, Xcel was aware of RPI‘s safety policies and procedures and could ensure that they were 

followed.
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Electrical problems that destroyed of penstock lighting, electrical junction boxes, and other

equipment.

Xcel welded a ―weep hole‖ inside the penstock on the day of the incident without issuing a 

hot work permit. Xcel‘s entry into the confined space lacked a confined space permit; that 

welding fumes could create a potential hazardous atmosphere was not analyzed.

The Xcel penstock project manager identified serious hazards in the penstock work, stating in 

an email that ―work conditions inside the penstock are highly hazardous on many levels.‖

Despite Xcel‘s knowledge of these serious safety problems, Xcel managers conducted safety observations 

of RPI‘s penstock activities on only two documented occasions: September 20, 2007 and October 1, 

2007. The project manger completed an inspection checklist, noting the ―extremely slick surfaces‖ inside 

the penstock. The penstock inspection form also stated ―environment continuously monitored,‖ but 

employee interviews and documentation indicate that the penstock was only periodically monitored at the 

access door entrance for hazardous atmospheres.95 An Xcel safety representative visited the penstock for a 

safety observation the day before the incident, during sandblasting operations. The completed safety 

observation form listed a number of worker protection categories that were marked off as satisfactory, 

unsatisfactory, or not applicable. The safety representative had marked the worker protection category of 

―confined space entry permit‖ as ―satisfactory.‖ The comments section noted that an RPI worker was at 

the penstock entrance accounting for the personnel inside. However, as discussed, RPI and Xcel had not 

effectively implemented important elements of a permit-required confined space program. For example, 

the confined space permits were only partially completed and RPI had not established acceptable entry 

 

95 A few witnesses stated that the RPI supervisor also occasionally monitored the air farther inside the penstock, but 

not on the day of the accident. There is, however, no documentation of these readings.
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conditions for the penstock. The form the project manager completed during the September 20 safety 

inspection similarly checked ―OK‖ under the category of confined space safety practices. 

8.2.3 Xcel Corporate Policies and Other Requirements Addressing 

Contractor Oversight

While Xcel‘s corporate policies and contracting documentation place primary responsibility for safety on 

the contractor for work under its control, Xcel policies also contain specific contractor safety oversight 

requirements. In the wake of the Cabin Creek incident, Xcel spokespersons stated that safety was RPI‘s 

responsibility and the contractors are ―experts in the field and that‘s why we hired them‖ (Lipsher, 

Mitchell, and McPhee, 2007). However, Xcel‘s ―Construction and Contractor Management‖ policy states: 

―[c]ontractor oversight or project control shall be established by both parties for all contracts with regard 

to health and safety standards.‖ Xcel‘s ―Contractor Safety‖ policy provides several contractor oversight 

requirements including the establishment of effective daily communication addressing safety issues 

between Xcel and the contractor, periodic jobsite visits by Xcel personnel to verify safety performance, 

and prompt notification and correction of deficiencies where violations of health and safety standards or 

regulations are discovered. Xcel‘s corporate policy is consistent with industry safety guidelines for owner 

oversight of contractor safety. CURT user practices recognize that ―[t]he owner must monitor contractor 

behavior to ensure effective implementation,‖ which includes auditing, measuring, and analyzing safety 

results, participating in incident investigation, and participating in contractor safety training (CURT, 

2004b, pp.7-9). 

However, Xcel ineffectively implemented its program for contractor safety oversight in a number of key 

areas identified by its contractor safety policy:

Xcel and RPI managers did not establish effective daily communication concerning the 

hazards associated with the penstock recoating project. Xcel did not effectively plan and 

coordinate with RPI to identify and control serious hazards in the recoating project, including 

the use of a flammable solvent within the penstock confined space. 
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The Xcel project manager or safety staff made documented safety observations only on two 

occasions at the penstock; these safety observations were ineffectively performed and failed 

to identify the serious confined space hazards.

Violations of Xcel safety standards and OSHA regulations were not promptly communicated 

and corrected. The serious safety issues that were known to Xcel during the penstock work 

did not lead to increased scrutiny of RPI or effective corrective action. 

Xcel acknowledged to the CSB that it had not audited the performance of its corporate contractor 

selection and safety oversight program prior to the incident. Periodic corporate audits play an important 

role in ensuring that safety policies and procedures are applied and effectively implemented so that safety 

hazards can be controlled or eliminated (ANSI/AIHA Z-10, 2005, p.25).

Xcel did not follow an effective contractor selection methodology that would ensure that contractors with 

a known unacceptable safety record would be disqualified from the bidding process. The company also 

failed to provide sufficient oversight to ensure that its contractors maintained a safe work environment 

while performing hazardous maintenance work at its Cabin Creek site.
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9.0 EMPLOYEE SAFETY TRAINING

Employee safety training is integral to the success of a company‘s safety and health program. First and 

foremost, the company is responsible for ensuring that its employees are trained and capable of 

conducting work safely.

96

Three broad types of training were available to RPI employees: 1) company-specific training provided by 

RPI; 2) general continuing education training provided through a union and the company partnership 

committee‘s Training Center; and 3) work-site specific training provided by RPI and Xcel. However, all 

of these modes of training were deficient in providing appropriate safety information to the penstock 

work crew, either by the administration of the training or the content of the material.

Specifically, the RPI employees were ill-prepared to safely conduct work inside the penstock because

RPI did not provide adequate training to its employees on its safety policies and procedures

RPI relied primarily on the partnership committee‘s Training Center to provide training to its 

employees, but the Training Center is not responsible for providing company- or site-specific 

training to its members; 

Only individuals hired as an apprentice or those specifically referred to the Training Center 

for enrollment in the apprenticeship program‘s semester-long courses receive the 

comprehensive and in-depth safety training the Training Center provides; consequently, just 

 

96 The American National Standard, ―Occupational Health and Safety Management Systems (OHSMS), 

ANSI/AIHA Z10-2005,‖ provides good practice guidance on training and competency. It states that the employer 

will ―establish processes to ensure through appropriate education, training or other methods that employees and 

contractors are aware of applicable OHSMS requirements and are competent to carry out their responsibilities as 

defined in the OHSMS‖ (ANSI/AIHA, 2005).
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two of the 14 contractors97 on the penstock project who had gone through portions of the 

program received some of this in-depth training. 

Employees referred to the Training Center for evaluation are assessed only on their technical 

painting skills, not their safety knowledge.

98 And because the two RPI employees referred by 

RPI to the Training Center had skill levels at or above a mid-level apprentice, they were not 

required to take the basic painting level courses that included much of the in-depth safety 

training.

Only nine of the 14 RPI employees received onsite training at Cabin Creek prior to the start 

of the recoating project, and that training was both abbreviated and did not effectively address

the hazards inherent to the penstock recoating work.

As a result, the RPI work crew received inadequate training on the specific and unique hazards of the 

penstock, including the safe handling of flammables, proper and safe use of spray equipment in a 

confined space, fire prevention and mitigation, and emergency response and rescue awareness. Had the 

existing apprenticeship safety training been provided to all journeyman painters, the RPI work crew 

would likely have been better prepared to manage the unique hazards of the penstock.

9.1 Company-Specific Safety Training

Employers are responsible for providing appropriate and effective safety training to its employees. RPI‘s

IIPP manual describes safe work practices and procedures on a wide array of safety issues, and while 

many are deficient (Section 6.6), a number address specific hazards that were associated with the 

penstock project, including the safe handling of flammables, proper confined space entry, and fire 

 

97 RPI had 14 employees working at the Cabin Creek site for the penstock recoating project; however, one left prior 

to the day of the incident for personal reasons. Twelve contractors and a general foreman remained on site.

98 The only safety issue individuals are evaluated on is their knowledge of proper PPE
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prevention. Training on the safety information within the IIPP manual likely would have mitigated some 

of the risks inherent with the recoating work. 

Unfortunately, the company‘s method to ensure that newly hired individuals understood the IIPP 

information was simply to have them sign off on a Certificate of Compliance, which states that the 

employee received the IIPP Manual and the Employee Safety Handbook and agrees to comply with the 

rules and practices of these documents. At the time of the incident, RPI did not test or otherwise verify

comprehension of the IIPP and its contents on an ongoing basis throughout an employee‘s career with the 

company. In fact, a 2006 audit of RPI by the SSPC found that RPI had ―[n]o documentation of craftworker assessment.‖ In response to this finding, RPI stated that it was ―currently implementing a training 

and documentation plan that will meet the requirements...‖ outlined in the audit. RPI went on to state that 

―[o]ur training[,] which will now be more stringently documented, will consist of; [sic] Ongoing Safety 

Training, Specialized Material Application Training, New Equipment Training, Site Specific 

Training...etc...).‖ Available evidence indicates that this training did not occur.

9.2 Training Center Safety Training

A Master Labor Agreement between the Painters and Allied Trades Union, District Council 36, and 

several participating multi-employer associations created the Southern California Painting and Drywall 

Industries (SCPDI) Joint Apprenticeship Training Committee and Center.

99 The SCPDI Training Center

is charged with providing an apprenticeship training program for beginners in the industrial painting 

trade. Integrated within this apprenticeship training program are a number of critical safety components.

Those who fully complete the program have the opportunity to build a solid foundation of technical 

painting skill and safety awareness.

 

99 This Committee, and its Training Center, is maintained through a Master Labor Agreement between the Painters 

and Allied Trades Union (District Council 36) and several contractor associations, of which RPI is a member.
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However, the number of individuals who benefit from the apprenticeship program training courses is

limited, in that the SCPDI Training Center is responsible for providing in-depth safety training only to 

individuals who are either just entering the industrial/commercial painting field or those referred to the 

Training Center by their employer for a skills evaluation and are subsequently found to be lacking in 

painting skills and abilities. None of the 14 RPI employees working on the penstock project were 

graduates of the apprenticeship program; only two were referred to the Training Center by RPI for skills 

evaluation. And because the two RPI employees referred to the Training Center had skill levels at or 

above a mid-level apprentice, they were not required to take the basic painting level courses that included 

much of the in-depth safety training.

Additionally, those referred to the Training Center are evaluated solely on technical painting skill and 

expertise; safety knowledge is not assessed as part of the evaluation process. An individual could qualify 

at the fourth stage within the seven-stage Apprenticeship Program based on his/her demonstrated 

knowledge of proper painting techniques and abilities, without having to demonstrate that he/she has the 

safety knowledge necessary to perform work at that painting skills level within the program. Indeed, the 

evaluation procedure utilized by the Training Center does not include an assessment of safety knowledge. 

Individuals that enter midway into the Apprenticeship Program miss out on multiple opportunities for indepth safety training, and those hired by the company and deemed sufficiently skilled in the trade are not 

sent to attend the semester-long Apprenticeship courses, and consequently are not exposed to the in-depth 

safety training. 

These training gaps are compounded because the Training Center does not, and is not expected or 

required to, provide instruction on company-specific policies or site-specific hazards.
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The SCPDI Training Center does offer general OSHA-required continuing education training 

opportunities100 to its union members; however, this training is not worksite-specific.

9.3 Generic Onsite Training Provided at Cabin Creek

The RPI work crew did not receive comprehensive safety training specifically pertaining to the penstock 

work environment from either their employer (RPI) or the host company (Xcel).

An Xcel safety supervisor, after reviewing RPI‘s penstock project bid submittal, noted that a number of 

the RPI employees lacked several training courses pertinent to the penstock work, including confined

space entry and electrical safety. He communicated this lapse in training to the RPI safety manager, who 

asserted that all RPI employees involved in the project would receive onsite training to cover these and 

other safety topics prior to starting work. The RPI safety manger asked a trainer at the SCDPI Training 

Center to come to the Cabin Creek site to provide basic OSHA-required continuing education/refresher 

training to the work crew. 

Only nine of the 14 RPI employees on the penstock project received this onsite training on September 10, 

2007. This training consisted of 6 hours of refresher-level safety review on six topics (each lasting about 

an hour). The contractors watched a safety video on each topic and were tested through multiple-choice 

exams. Those who had not arrived onsite until after September 10 were not provided an opportunity to 

take a make-up session. 

In testimony to the CSB, the trainer stated that the review of safety topics was kept ―pretty brief‖ because 

the contractors had attended the refresher courses multiple times. While repetition may seem burdensome, 

the real challenge in preparing for safe work is to ask: What about this job and these planned activities are 

 

100 CPR, Respirator Use and Fit Test, and Lead Worker Refresher is required annually; First Aid is required every 

three years; and the following courses are reviewed at least once per year in the Apprenticeship program but 

journeymen are required to take the training only once: Fall Protection, Scaffold/Swing Stage, Confined Space 

Awareness, Hazard Communication, Hearing Protection, Asbestos Awareness, Aerial Mobile Power Lifts, Forklift 

& Drywall. 
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different from what we‘ve done before? What are the hazards of those different activities? How can that 

risk be eliminated or controlled?

101 Approaching hazards this way focuses attention on the risks that may 

not be readily apparent when reviewing generic training materials before the start of work.

The onsite training for the RPI employees was brief and generic and included only a basic review of 

confined space awareness. It included an overview of the definition of a confined space, but not how to 

evaluate a confined space for potential hazards, how to properly complete confined space entry forms, or 

how to prepare and arrange methods for evacuation. The onsite training also included a basic review of 

electrical safety, the material provided focused on the importance of using grounded equipment and 

following lockout/tagout procedures, but not on the need to use conductive hoses to prevent static 

discharge, nor did it explicitly instruct the crew about how to wire and ground equipment properly for 

safe use.

The hazardous communication training on September 10 did not include a site-specific discussion of safe 

use of flammable solvents in confined spaces, despite plans by both companies to use a solvent within the 

penstock during the recoating process102 (Section 6.5). Nor were flammable and explosive atmospheres,

fire prevention, and fire extinguisher use within the penstock incorporated in any onsite training for the 

contractors; also excluded was a discussion of procedures for emergency evacuation of the penstock. 

Neither Xcel nor RPI discussed the lack of a secondary egress with the work crew during the onsite

training, and specific emergency response and rescue training did not extend beyond the instruction to the 

crew to call the Xcel control room for 9-1-1 services if an emergency should arise.103

 

101 A U.S. aircraft commander, who is also a human performance specialist, often prepares his crews by asking, 

―What is dumb, different, and dangerous about this specific mission?‖ to provoke their collective thinking about 

the specific and potentially unique risks of a given mission. 

102The hazardous communication training on September 10 consisted of an employee‘s right to know the chemicals 

onsite, how to read an MSDS, and proper PPE.

103 One likely reason for the lack of pertinent training on the issues inherent with the penstock project work was the 

trainer‘s lack of penstock experience. The trainer relied on a more experienced contractor within the RPI crew to 
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The RPI employees also received a brief onsite safety overview from Xcel as they arrived at Cabin Creek 

and began preparing for work inside the penstock.

104 This brief orientation – consisting of a checklist 

review of potential hazards – was held on three separate occasions, led by different Xcel personnel and 

attended by various crew members.

105 The orientation provider addressed confined space by asking the 

RPI crew if they had been trained on the safety topic, but the provider did not verify this training, nor 

were MSDSs of chemicals to be used within the penstock discussed or requested. The orientation did not 

cover a number of safety issues related to the penstock work, including emergency response and 

evacuation plans or safeguards for minimizing fire hazards within the confined space.

9.4 Safety Training Needs Specific to the Penstock 

The unique characteristics of the penstock and the recoating work require knowledge and skill on a 

number of safety topics, including the safe handling and use of flammables, confined space entry and 

monitoring, fire prevention, and emergency preparedness. Many of these safety topics are covered 

effectively in the SCPDI apprenticeship program; others are covered within the safety policies of the host 

and contractor companies. Through interview testimony and training records, the CSB found that the 

necessary safety information pertaining to the penstock project was not, in most cases, effectively

administered to the RPI workforce, nor did either company uphold and reinforce safe work practices at 

the work site. This section identifies where safety training and information existed but was not 

incorporated into the work activities at Cabin Creek.

 

inform the others of the penstock‘s hazards; however, according to witness testimony, the experienced contractor 

focused on slip, trip and fall hazards, not on the major confined space hazards of the penstock or the risks of 

working in flammable atmospheres.

104 This orientation was meant to focus on Xcel policies and procedures; topics covered included lockout/tagout, 

forklift use, slipping hazards, and waste removal from the site.

105 Each member attended the orientation once.
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9.4.1 Substituting Non-flammables for Flammable Solvents

The use of potentially safer alternatives to MEK is discussed in the SCPDI apprenticeship program‘s 

training course, ―Solvent and Hazardous Materials.‖ The training materials state: ―Whenever possible, 

organic solvents should be replaced with either water-based solvents or another less harmful organic 

solvent.‖ The importance of exploring opportunities to exchange flammable solvents for non-flammable 

substitutes is reiterated throughout the training materials, which provide a substitution example dealing 

explicitly with MEK: ―a citrus based [sic] cleaner could be used in place of MEK for tool clean up.‖ Only 

one RPI crew member attended the ―Solvent and Hazardous Materials‖ course (as part of his training 

through the Apprenticeship program). The use of a non-flammable solvent would have prevented the 

Cabin Creek fire. 

9.4.2 Safe Handling and Use of Flammables

Training on the safe handling and use of flammables is offered only to employees who are going through 

the apprenticeship program or when specifically requested by a company. The IIPP safety policies 

concerning the safe handling and use of flammables were not provided to employees through in-house 

company-provided training, nor were employees‘ comprehension of these polices assessed.

106 As a result, 

RPI employees were not sufficiently trained on the safe use of flammables.

The proper and safe handling of flammables is covered in the ―Basics of Solvents and Thinners‖ and 

―Solvent and Hazardous Materials‖ training courses the SCPDI Training Center offers. However, records 

going back five years prior to the incident show that none of the RPI employees working inside the 

penstock took the ―Basics of Solvents and Thinners‖ course and, as stated, only one of the crew took the 

―Solvent and Hazardous Materials‖ training course. 

 

106 When subpoenaed for all training materials, RPI did not provide any documentation that employees were tested 

on the IIPP safety information.
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The ―Basics of Solvents and Thinners‖ course materials provide many warnings about the risks of using 

flammables, and the ―Solvents and Hazardous Materials‖ course goes further, stating: ―NEVER leave 

solvent products open when not in use‖ (emphasis in original) and ―Place solvent soaked rags or materials 

in all-metal containers with tight sealing tops‖ to prevent dangerous vapor accumulation in the work area. 

The training materials also warn: ―Transport and store solvents ONLY in approved, properly labeled and 

marked containers‖ (emphasis in original). By following these safety rules, the training material asserts, 

the chance for a fire or explosion is reduced. 

Some RPI employees stated they knew how to safely transfer flammables, but as metal safety cans for 

MEK transfer were not made available for use at Cabin Creek, adhering to this safety policy was 

impossible. 

9.4.3 Flammable Atmospheres and Confined Space Entry

SCPDI Training Center training materials for ―Confined Space Entry‖ state: ―If the atmosphere contains 

flammable gas, vapor or mist in excess of 10 percent of its lower flammable limit (LFL), that atmosphere 

is not acceptable for entry.‖ Yet on October 2, 2007, the Cabin Creek confined space work did not 

prohibit entry or occupancy of the penstock where the LFL was in excess of 10 percent, nor did Xcel or 

RPI‘s policies require this safeguard. The attendant was conducting atmospheric monitoring at the access 

door, more than 1,450 feet (442 meters) away from the crew using the solvent to flush the hoses, wands, 

and sprayer system with MEK, which was too far away to get an accurate measurement. MEK vapor 

produced with the flushing activities resulted in the accumulation of solvent vapors to levels above the 

maximum allowable for entry around the equipment and work crew.

9.4.4 Fire Prevention and Mitigation 

Both the SCPDI fire prevention training course material and RPI‘s IIPP section, ―Fire Protection and 

Prevention,‖ stress the importance of both clear access to emergency response equipment and its 

placement close to the actual painting operation. Yet RPI provided only six of the 14 contractors with a 
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general course on proper fire extinguisher placement within the worksite; this training occurred 

approximately two months prior to the incident.

The SCPDI fire prevention training also included instructions that there should be more than one exit in 

the area of work and that all workers keep their backs to an exit in case a fire necessitated escape. Despite 

these fire safety recommendations, the arrangement of spray equipment within the narrow confines of the 

penstock kept contractors separated from the work area‘s only exit. No remedial action was taken to

address the lack of a secondary exit, although a number of RPI employees expressed concern about 

having only one egress point. The positive affects of training are significantly diminished when the good 

practices promoted in the training cannot be adhered to. Interestingly, a penstock project contract 

addendum, which both Xcel and RPI agreed to, empowered Xcel employees with ―stop work authority‖ 

during the project, allowing Xcel employees to order RPI to cease work within the penstock if they 

observed unsafe work practices. This stop work authority was given specifically to Xcel employees, not 

the RPI work crew. 

9.4.5 Proper and Safe Use of the Sprayer and Associated Equipment

RPI employees were not trained on the proper and safe use of the Graco epoxy sprayer system. The 

SCPDI Training Center does not train on Graco spray equipment exclusively, but a plural component 

(two-part) spray system is a topic within the apprentice spray painting course curriculum. However, only 

two of the 14 contractors went through the apprenticeship semester course that covers this information. 

This training, which was provided by a third party in agreement with RPI, had taken place two years prior 

to the penstock project. Working with unfamiliar equipment likely contributed to the operational 

problems the crew was experiencing during their application attempts.

The RPI crew working inside the penstock lacked the in-depth safety training and knowledge necessary to 

work safely within this unique and challenging confined space environment. RPI did not provide adequate 

training addressing the safety risks of the penstock recoating work to its employees. The Training Center 
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Apprenticeship Program does provide comprehensive safety training; however, few RPI employees

received this in-depth safety training. 
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10.0 Regulatory and Industry Standards Analysis

RPI‘s and Xcel‘s policies and permits failed to established safe limits that prohibit entry or occupancy of 

a confined space with a hazardous flammable atmosphere. However, existing federal regulations for 

general industry do not require that employers establish such safety limits. Specifically, the current OSHA 

Permit-Required Confined Spaces Rule does not prohibit entry or occupancy in a confined space above a 

maximum permissible percentage of the LFL nor does it require continuous monitoring throughout the 

duration of the work107 to ensure the concentration of flammable gases does not exceed that percentage. 

The CSB determined that, even if combustible gas monitoring had been performed on the day of the 

incident in the area where flammable solvent was being used, this monitoring would likely not have been 

enough to prevent the initial flash fire in the penstock; with no set limit for flammable atmospheres, the 

RPI crew had no evaluation and action level in which to use to determine when it was safe to work and 

when cessation and/or evacuation was necessary. 

10.1 Hazards of Confined Space Work in Potentially Flammable 

Atmospheres Inadequately Covered in Existing Standards

OSHA‘s Permit-Required Confined Spaces Rule for general industry states that a confined space must be 

permit-required when the space has a potential to contain a hazardous atmosphere, which is defined for 

flammables as an atmosphere that exceeds 10 percent of the LFL [29 CFR 1910.146(b)] (Section 6.1). A 

permit-required confined space program mandates that employers specify acceptable entry conditions and 

take actions such as purging or ventilating the space to eliminate or control atmospheric hazards such as a 

flammable atmosphere [29 CFR 1910.146(d)(3)(i), (iv)]. However, the rule does not define acceptable 

 

107 In this incident, the penstock space was ―large or...part of a continuous system,‖ which would require continuous 

monitoring (See Sections 6.1.3 and 11.2.2.2, which discuss 29 CFR 1910.146 (d)(5)(i)). However, the fact alone 

that a flammable was being used within a confined space would not have triggered the requirement for continuous 

monitoring.
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entry conditions or specify what additional precautions must be taken for working in a permit-required 

confined space with a potential flammable atmosphere, nor does it limit entry based upon measureable 

critieria such as a specific maximum percentage of the LFL, even though OSHA defines an atmosphere as 

hazardous when it exceeds 10 percent of the LFL. Appendix C of the rule gives examples of permitrequired programs, including a scenario where interior coatings/linings are applied in portable tanks. This 

scenario describes an approach to control the hazards by establishing forced air ventilation to keep the 

potentially flammable atmosphere below 10 percent of the LFL [29 CFR 1910.146 Appendix C, Example 

3]. However, Appendix C provides only examples of permit-required programs; it does not establish 

enforceable requirements.

In 1996, OSHA issued a letter of interpretation that allows work to be performed in atmospheres in excess 

of 10 percent of the LFL, stating that when the atmosphere is above 10 percent, ―all of the requirements 

of the rule must be met‖; however, it provides no specific safety guidance (OSHA, 1996). The letter 

concludes that because the Permit-Required Confined Spaces Rule for general industry is a performance 

standard, ―it does not specify procedures for conditions where the permit-required space has a hazardous 

flammable atmosphere‖ (OSHA, 1996). Rather, the employer must implement control measures based 

upon a hazard analysis of the ―the means, procedures, and practices necessary for safe permit space entry 

operations‖ [29 CFR 1910.146(d)(3)]. In fact, the letter does not suggest any limits on entry based on 

measurements of the flammable atmosphere or even that safe entry conditions need be defined in terms of 

the LFL, which directly contradicts the more recent OSHA shipyard standards and recent NFPA 

guidance, as discussed below. 

The Permit-Required Confined Spaces Rule requires ―purging, inerting, flushing or ventilating the permit 

space as necessary to eliminate or control atmospheric hazards‖ [29 CFR 1910.146(d)(3)(iv)]. Under the 

rule, a hazardous atmosphere is one ―that may expose employees to the risk of death, incapacitation, 

impairment of ability to self-rescue...injury, or acute illness‖ [29 CFR 1910.146(b)]. The logic of the 

provisions would appear to demand that for safe entry, the confined space flammable atmosphere would 
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need to be reduced to 10 percent or less of the LFL or inerted to prevent the formation of a flammable 

mixture inside the permit space and the possibility of death or injury; however, the Rule has no such 

explicit requirement. 

The following support the need for effective requirements or limits for working in flammable 

atmospheres in terms of confined space entry and occupancy: 

1. Establishing safe flammable limits as a percentage of the LFL, with the effective use of 

appropriate monitoring devices (e.g., combustible gas detectors), is an accurate method for 

obtaining quantitative data to evaluate the potential degree of hazard and protect personnel 

(McManus, 1999, p.748).

2. Safe flammable atmosphere limits are needed because no adequate PPE is available that can 

protect workers from an explosion within a confined space (NFPA 1006, 2008).

3. Sources of ignition for a fire or explosion are typically plentiful and difficult to eliminate entirely, 

as illustrated in the number of possible ignition sources available in the Cabin Creek penstock; as 

such ―there is no ready assurance that all sources of ignition could be eliminated‖ (McManus, 

1999, p.746).

4. Lacking specific regulatory requirements based upon measureable parameters, employers may 

fail to establish adequately protective limits for working in potentially flammable atmospheres. In 

this incident, neither Xcel nor RPI had established safe entry conditions for flammable 

atmospheres based upon a percentage of the LFL in their procedures and permits.

5. Failure to establish safe flammable limits undermines the importance of monitoring in permitrequired confined spaces; the need for periodic or continuous monitoring will not be understood 

by employers and personnel if no limits are specified. This safety gap can lead to a failure to 

conduct critical combustible gas testing in appropriate locations and with the needed frequency, 

as was the case in the Cabin Creek penstock.
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6. Unlike flammable atmospheres, other atmospheric hazards have explicit and measureable 

requirements elsewhere in the OSHA regulatory scheme to confirm compliance with the PermitRequired Confined Spaces Rule. For example, OSHA standards for toxic substances establish 

quantitative permissible exposure limits and other standards require quantitative monitoring of 

potentially oxygen-deficient atmospheres.108

7. Confined space entry is a frequent activity in U.S. workplaces-OSHA estimates that more than 

4.7 million permit-required confined spaces are entered by workers annually (OSHA, September 

2008).

8. A flammable atmosphere is a serious confined space hazard. According to noted confined space 

expert McManus (1999), fires and explosions are a ―major cause‖ of deaths and injuries in 

confined spaces and have led to a relatively ―large portion of fatalities per incident compared to 

other situations‖ (p. 112). The CSB concluded that serious confined space incidents involving 

flammable atmospheres are still a significant problem and that adequate combustible gas 

monitoring, clearly defined limits for working safely in potentially flammable atmospheres, and 

other control measures such as eliminating the hazard or adequate ventilation of the space can 

prevent these accidents (Section 11.0).

10.2 Other Regulations and Safety Guidelines Set Protective LEL 

Limits for Work in Potentially Flammable Atmospheres

The approach in the Confined Spaces Rule sharply contrasts with more stringent, recently promulgated 

OSHA standards, such as those for confined spaces in shipyard employment [29 CFR 1915, Subpart B], 

which limit work activities that can be conducted in atmospheres that exceed 10 percent of the LEL. The 

shipyard standard requires that confined spaces containing a flammable concentration of 10 percent of the 

 

108 For example, see OSHA‘s Table Z-1, ―Limits for Air Contaminants‖; 29 CFR 1910.1000; and the Respiratory 

Protection Standard, 29 CFR 1910.134. 
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LEL or higher be labeled as ―Not Safe for Workers‖ [29 CFR 1915.12(b)(2)]. In the discussion related to 

the final rule for confined spaces in shipyard employment, OSHA argued that adopting 10 percent of the 

LEL limit for safe occupancy was more appropriate than other proposed levels: ―The Agency believes 

that a compartment in which any portion is above 10% of the LEL is unsafe‖ [59 FR 37816-37863].

Yet the general industry Permit-Required Confined Spaces Rule allows employers to adopt limits higher 

than 10 percent of the LEL as an acceptable entry condition. McManus, in Safety and Health in Confined 

Spaces (1999), defends the use of lower LEL limits, noting that conducting a confined space hazard 

analysis can be difficult and uncertain because of several factors: 1) the accurate detection of ignitable 

atmospheres depends on the position of the intake of the instrument relative to the source, 2) the relative 

response of the sensor based the on substance(s) being sampled to the substance(s) used to calibrate the 

sampler, and 3) the timing of the samples (pp. 745-752).109

A number of organizations, standard-setting bodies, and other government regulatory agencies have also 

adopted guidelines that prohibit or limit work activities in confined spaces in atmospheres above 10 

percent of the LEL (Appendix G). McManus (1999) suggests that ―[t]he consensus expressed through 

more recent standards indicates decreased tolerance‖ for hazardous flammable atmospheres (p. 745). An 

important example of this trend can be found in the 2008 edition of NFPA 1006, Standard for Technical 

Rescuer Professional Qualifications. This consensus standard addresses acceptable entry conditions for 

confined space rescue and states in its explanatory material that ―[r]escuers should not enter confined 

spaces containing atmospheres greater than 10 percent of a material‘s LEL, regardless of the personnel 

protective equipment worn. There is no adequate protection for an explosion within a confined space‖ 

[NFPA 1006, 2008, Annex A.7.1.1].

 

109 Webber (2007) summarizes relevant research showing conditions where flammable vapors can be ignited even 

when concentrations are below the LEL that result in localized flash fires.
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A number of other confined space consensus safety standards and industry guidelines recommend special 

precautions to detect and control flammable atmospheres and explicitly establish safe work limits for 

confined spaces that are substantially below the LFL, such as 10 percent of the LFL [ANSI Z117.1, 2009, 

p.24; ASTM D4276-02, 2007, p.3; NFPA 326, 2005; API 2015, 2001a, p.28; API 2016, 2001b, pp.43, 60; 

IChemE, 2005, p.66]. 

NFPA 326, Standard for the Safeguarding of Tanks and Containers for Entry, Cleaning, or Repair,

requires that ―[a]ll work in or around the tank or container shall be stopped immediately when the 

flammable vapors in the atmosphere exceed 10% of the lower flammability limit (LFL). The source of the 

vapors shall be located and eliminated or controlled‖ [NFPA 326, 2005, p.9]. A number of countries 

including Australia, New Zealand, and nearly all Canadian provinces prohibit confined space entry above 

a defined safe flammable atmosphere limit that is substantially below the LEL (Appendix G). 

Therefore, in light of the existing consensus of confined space codes and regulations establishing lower 

LEL limits for safe entry and the improved understanding of the increased hazards of working in permit 

spaces in atmospheres above 10% of the LEL, the CSB recommends that OSHA limit confined space 

work activities in the presence of flammables in the same manner and to the same degree as the agency 

has done in shipyards and as many other consensus standards recommend.

10.3 Colorado Public Utilities Commission

The Colorado Public Utilities Commission (PUC) is a state regulatory agency that oversees a wide variety 

of electric power and other utilities. Xcel is one of two investor-owned electric utilities operating in 

Colorado that are regulated by the PUC. The stated mission of the PUC is to serve the public interest ―by 

effectively regulating utilities and facilities so that the people of Colorado receive safe, reliable, and 
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reasonably priced services consistent with the economic, environmental and social values of our state.‖110

The PUC has promulgated the Rules Regulating Electric Utilities (4 Code of Colorado Regulations 723-3, 

Part 3) that address a range of subjects including safety; construction, maintenance, and operation of 

electric utility facilities; and competitive bidding processes related to areas such as the acquisition of new 

utility resources. 

The PUC rules require that the construction, maintenance, and operation of a utility be ―in accordance 

with accepted engineering practice in the electric industry to assure continuity of service, uniformity in 

the quality of service, and the safety of persons and property.‖111 The PUC rules provide that in the event 

of an incident resulting in death, serious injury, or significant property damage, the regulated utility shall 

inform the Commission within two hours of learning of the incident and submit a written report within 30 

days.112 The only content requirements of the written report are the date, time, place, location, and type of 

the incident; names of persons involved; and nature and extent of injury and damage. For the Cabin Creek 

incident Xcel sent a one-page letter to the PUC on November 1, 2007, briefly describing the incident and 

the number of people killed and injured. PUC rules state that if a utility conducts an internal investigation 

of an incident that any report developed shall be made available to the Commission upon request.113 The 

PUC Commission was not notified of the availability of any internal investigation report by Xcel nor did 

the Commission receive any report. Xcel did not inform the Commission of the root causes of the Cabin 

Creek incident, recommendations for prevention, or any subsequent preventative measures taken by Xcel.

PUC electric utility contracting rules describe procedural requirements and criteria other than price to 

consider in the competitive bidding process but the provisions do not include any safety considerations. 

 

110 Mission of the Public Utilities Commission, http://www.dora.state.co.us/puc/about/AboutMission.htm

accessed 7-13-10. 

111 Colorado Department of Regulatory Agencies, 4 Code of Colorado Regulations (CCR) 723-3, Part 3, Rules 

Regulating Electric Utilities, Rule 3200(a), Construction, Installation, Maintenance, and Operation.

112 Id. Section 3204(a) and (b).

113 Id. Section 3204(c). 
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The rules contain provisions that regulate resource planning such as those resources that provide electrical 

capacity and renewable energy. The acquisition of utility resources can include new construction, 

maintenance, and repairs that significantly impact capacity or prevent service interuption. PUC rules 

favor competitive bidding for the acquisition of new resources and address requirements for the

competitive bidding processes, requests for proposals (RPFs) and bid evaluation criteria. In 2010, the 

Colorado General Assembly approved renewable energy legislation that requires the Colorado Public 

utilities Commission to implement new ―best value‖ contracting bid criteria for electric resource 

acquisition114. The additional criteria that need to be considered in the competitive bidding process 

include workforce training certifications, long-term career opportunities, and industry standard health care 

benefits. However, neither the existing PUC rules nor the new mandated criteria require that past safety 

performance be considered as a factor in the competitive bidding process, nor do they include safety 

prequalification or disqualification procedures. 

 

114 The 2010 Colorado General Assembly amended Colorado Revised Statutes 40-2-124 by House Bill 10-1001, 

http://www.dora.state.co.us/PUC/rulemaking/HB10-1001/HB10-1001_enr.pdf , accessed 7-13-10.
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11.0 Flammables Used in Confined Spaces: Other Incidents

As part of its investigation of the Xcel penstock case, the CSB collected and compiled confined space 

incident data from the past 17 years to ascertain the prevalence of confined space flammable incidents and 

determine if the rate has been impacted by the promulgation of the Permit-Required Confined Spaces 

Rule. The CSB has determined that the hazard of flammable atmospheres in confined spaces has been a 

significant workplace safety issue since the promulgation of OSHA‘s Permit-Required Confined Space 

Rule on April 15, 1993. 

The CSB compiled and researched incident data on 105 previous confined space incidents; of these, 53 

were determined to be the result of a flammable atmosphere in a confined space. (Appendix I describes

CSB‘s incident data collection methodology used to obtain this data.) The CSB also found that the

number of confined space flammable incidents has increased the past nine years, as a majority of the 53

incidents from 1993 until April 2010 occurred since 2003. These flammable atmosphere confined space 

incidents include two the CSB investigated in 2009 that resulted in four fatalities (Appendix J).

The 53 identified confined space flammable incidents caused 45 fatalities and 54 injuries from 1993 to 

April 2010; approximately 57 percent included a fatality. The number of fatalities and injuries increased 

in the 17 years, with 49 percent of the total fatalities and approximately 57 percent of total injuries 

occurring since 2003. In the past 14 months, from February 2009 to April 2010, the CSB identified seven 

additional confined space incidents that resulted in six fatalities and four injuries. 

The CSB analysis shows that a flammable atmosphere was present in the confined space prior to entry in 

60 percent of the incidents sampled. Flammables were brought into the confined space for activities like 

painting/recoating, cleaning, or welding in the remaining approximately 40 percent. This data underscores 

the importance of monitoring the confined space both before entry and continuously in the work area 

where the confined space work activity includes the use of flammables. Continuous monitoring under

these circumstances combined with flammable atmosphere limits established in procedures and permits 
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are likely to alert workers to the importance of rapid changes that can lead to a flammable atmosphere so 

that workers can evacuate.115

The data suggest that, even after the promulgation of the Permit-Required Confined Space Rule, a 

significant number of confined space incidents with fatalities and serious injuries were attributed to 

flammable atmospheres. Furthermore, the increasing numbers of fatalities and injuries post-promulgation 

of the Permit-Required Confined Spaces Rule suggests the need for more protective requirements for 

work in potential flammable atmospheres in confined spaces.

 

115 An example of how continuous monitoring can prevent worker fatality or injury is evident from a confined space 

incident that occurred on January 7, 2010 in Amsterdam, NY. Two telephone workers were conducting repair 

work in a telephone vault (similar to a manhole) when their combustible gas meter alarmed. They were able to 

evacuate the confined space prior to a small fire breaking out. 
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12.0 ROOT AND CONTRIBUTING CAUSES

12.1 Root Causes

1. Xcel and RPI management did not ensure effective planning and coordination of the Cabin Creek 

penstock recoating project to control or eliminate the serious confined space hazards that were 

present. 

An effective hazard evaluation of the penstock confined space was not performed; the work 

required the use of a solvent to clean the epoxy sprayer and associated equipment in the open 

penstock atmosphere, yet the serious safety hazards of using a flammable solvent inside the 

confined space were not identified or addressed. 

Substituting a non-flammable solvent was not considered.

Important safety precautions when using a flammable in a confined space, such as continuous 

monitoring in the work area, providing adequate ventilation, and eliminating or controlling 

ignition sources, were not implemented.

2. Xcel‘s and RPI‘s corporate safety policies and permits did not effectively establish safe limits for 

flammable atmospheres in permit-required confined spaces that would prohibit entry or 

occupancy when those limits were exceeded.

3. Early in the planning process, Xcel identified the Cabin Creek penstock‘s single point of egress in 

the event of an emergency as a major concern; RPI personnel also raised safety issues about a 

single exit. However, neither Xcel nor RPI management took remedial action.

American Society of Civil Engineering (ASCE) published safety guidance addressing 

penstock inspections advises on the importance of alternative escape routes in the event of an 

emergency (ASCE, 1998, p.2-8).
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As a result of the flash fire, five RPI workers, who were located on the side of the sprayer 

opposite the sole exit, were trapped by the growing flames and eventually succumbed to 

smoke inhalation. 

4. Xcel management did not provide effective oversight of RPI to ensure the penstock recoating 

work was safely conducted.

Due to concerns about RPI‘s record of injuries and fatalities in past projects, Xcel added a 

‖Safety Addendum‖ to the penstock recoating contract affirming that Xcel would closely 

observe RPI‘s safety performance. However, Xcel managers conducted safety observations of 

RPI on only two documented occasions in the 29 days that RPI personnel were on the job. 

During the penstock recoating work prior to the incident, Xcel managers were aware of 

several significant safety problems attributable to RPI, yet Xcel did not increase scrutiny of 

RPI‘s safety performance or implement corrective actions.

12.2 Contributing Causes

1. Xcel‘s corporate policies and practices addressing contractor selection did not adequately ensure 

contractor safety performance for the penstock recoating project.

During the contractor selection process, Xcel managers graded RPI safety performance as a 

zero, the lowest possible score; however, Xcel‘s contractor selection practices typically

provided only for disqualification from the bidding process based upon financial capacity, not 

safety criteria.

The evaluation rating form stated that the score of zero did not met Xcel‘s minimum 

requirements and required automatic rejection; however, RPI was still allowed to compete for 

the penstock recoating contract. RPI‘s proposal was ranked as the best overall based 

primarily on its low price.
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RPI did not disclose to Xcel regulatory violations resolved within the requested three-year 

period as part of the RFP evaluation process. Xcel‘s corporate policies addressing contractor 

selection relied upon self-reporting and did not include specific procedures to verify the 

contractor‘s submissions.

2. Xcel and RPI managers did not plan and coordinate the immediate availability of qualified 

confined space technical rescuers outside the penstock, although the use of flammable solvent in

the open atmoshere of the permit space created the need for immediate rescue due to the potential 

for IDLH conditions. 

Neither company ensured that emergency response organizations or personnel with confined 

space technical rescue qualifications were immediately available with the necessary firefighting equipment outside the penstock. 

The approximate travel time of the closest identified public emergency response organization 

with confined space technical rescue qualifications was approximately 1 hour and 15 minutes.

After the penstock fire erupted, firefighting and rescue activities likely would have been

sucessfully provided to prevent the fatalities had qualified personnel and equipment been 

immediately available; the trapped RPI workers were in radio communication with coworkers 

and emergency responders for 45 minutes after the initial 9-1-1 call.

3. RPI did not ensure that the majority of its workforce at Cabin Creek had received comprehensive 

formal safety training, effective training on company safety policies, or site-specific instruction 

addressing confined space safety, the safe handling of flammable liquids, the hazard of static 

discharge, emergency response and rescue awareness, and fire prevention. 
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13.0 RECOMMENDATIONS

Occupational Safety and Health Administration (OSHA) 

2008-01-I-CO-R1 Amend the OSHA Permit-Required Confined Spaces Rule for general industry

(29 CFR 1910.146) to establish a maximum permissible percentage substantially 

below the lower explosive limit (LEL) for safe entry and occupancy in permitrequired confined spaces.

2008-01-I-CO-R2 Publish a ―Safety and Health Information Bulletin‖ addressing the hazards and 

controls when using flammable materials in confined spaces that includes 

actionable guidance regarding:

a. The importance of implementing a hierarchy of controls to address 

hazards in a confined space that first seeks to eliminate hazards or 

substitute with a less hazardous material(s) or method(s). Examples 

include performing work outside of a confined space where reasonably 

practicable or substituting a flammable material with a non-flammable 

one. 

b. The necessity of establishing a maximum permissible percentage 

substantially below the lower explosive limit (LEL) for safe entry and 

occupancy of permit required confined spaces. 

c. The need to comprehensively control all potential ignition sources and 

continuously monitor the confined space at appropriate locations and 

elevations when work activities involve the use of flammable materials 

or where flammable atmospheres may be created.

d. The importance of treating confined spaces with the potential for 

flammable atmospheres above 10 percent of the LEL as a hazard 
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immediately dangerous to life or health (IDLH) that requires rescuers to 

be stationed directly outside the permit space and available for 

immediate rescue with appropriate fire-extinguishing and rescue 

equipment. 

e. The requirement that confined spaces such as penstocks be managed as 

permit-required that are so large or part of a continuous system that they 

cannot be fully characterized from the entry point. Such spaces need to 

be monitored for hazardous atmospheres both prior to entry and 

continuously in areas where entrants are working.

The Governor of the State of Colorado

2008-01-I-CO-R3 Implement, through the Division of Fire Safety, an accredited firefighter 

certification program for technical rescue that encompasses appropriate specialty 

areas including confined space rescue.

The Colorado Public Utilities Commission

Revise your rules regulating electric utilities, 4 Code of Colorado Regulations 723-3, to:

2008-01-I-CO-R4

a. Require regulated utilities to investigate the facts, conditions, and circumstances 

of all incidents resulting in death, serious injury or significant property damage 

as defined in Section 3204

b. Require utilities to submit a written investigation report to the Commission 

within one year of the incident that contains the investigation findings, root 

causes and recommendations for preventing future incidents that focus on needed 

changes to utility safety systems. All reports shall be made public.
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c. Authorize the commission to issue orders addressing needed corrective actions to 

be taken as a result of the incident. 

d. Require utilities to submit periodic reports to the Commission detailing action 

taken on the incident report recommendations and Commission orders. All 

reports shall be made the public.

2008-01-I-CO-R5

Require all regulated utilities to fully cooperate with all government safety 

investigations including facilitating access to witnesses, facilities, and equipment; 

providing copies of requested records; and responding to interrogatories and other 

investigative requests for information as expeditiously as possible.

2008-01-I-CO-R6

Require that competitive bidding and contractor selection rules for construction, 

maintenance or repair of regulated utilities include procedures for prequalifying or 

disqualifying contractors based on specific safety performance measures and 

qualifications.

Director of the Division of Fire Safety and the Director the Division of Emergency 

Management for the State of Colorado

2008-01-I-CO-R7 Publish a safety communication that will inform fire service and emergency 

planning organizations in the state about the confined space safety lessons 

learned from the Cabin Creek incident including

a. The need to train and certify emergency response personnel who perform 

technical, including confined space, rescue.

b. The importance of a written confined space rescue plan for each 

designated permit space that includes 
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i. Methods of rescue and determination of whether a rescue 

team is required to standby outside the space.

ii. Rescue equipment requirements and plan of action. 

c. The importance of treating confined spaces with the potential for 

flammable atmospheres above 10 percent of the LEL as a hazard 

immediately dangerous to life or health that requires rescuers to be 

stationed directly outside the permit space and available for immediate 

rescue with appropriate fire-extinguishing and rescue equipment. 

d. The need for confined space rescue procedures to instruct emergency 

responders to not enter or occupy a confined space containing a 

flammable atmosphere 10 percent of the LEL or greater. Personal 

protective equipment (PPE) will not protect rescuers from an explosion 

in a confined space. 

Xcel Energy, Inc.

2008-01-I-CO-R8 Revise your policies for solicitation and procurement of construction services to 

a. Ensure that requests for proposals (RFPs) and selection processes include 

criteria and procedures for prequalifying or disqualifying contractors 

based on specific safety performance measures and qualifications.

b. Implement written verification procedures for the safety information and 

documentation submitted by contractors during the bidding and selection 

process.

2008-01-I-CO-R9 Revise your contractor safety policies to require a comprehensive review and 

evaluation of contractor safety policies and procedures such as the permitrequired confined space program and safety performance of contractors working 
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in confined spaces to ensure that any bidding contractor meets or exceeds Xcel 

Energy safety requirements.

2008-01-I-CO-R10 Conduct periodic safety audits of contractor selection and oversight at your 

power-generating facilities to ensure adherence to corporate contractor 

procurement and safety policies.

2008-01-I-CO-R11 Report key findings, causes and recommendations of the CSB report to Xcel 

shareholders so that the owners of Xcel are fully informed of the report contents 

and how Xcel intends to prevent a similar accident in the future.

Xcel Energy, Inc. 2008-01-I-CO-R12

See below for recommendation text.

RPI Coating Inc. 2008-01-I-CO-R13

Revise your confined space entry program and practices. At a minimum

a. Require continuous monitoring for flammable atmospheres at 

appropriate locations and elevations within a confined space where work 

activities involve the use of flammables or where flammable 

atmospheres may be created. 

b. Prohibit entry or require evacuation of a confined space if the 

atmospheric concentration of flammable vapors is 10 percent of the LEL 

or higher.

c. Ensure that confined spaces such as penstocks be managed as permitrequired that are so large or part of a continuous system that they cannot 

be fully characterized from the entry point. Ensure that such spaces are 
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monitored for hazardous atmospheres both prior to entry and 

continuously in areas where entrants are working.

d. Ensure that evacuation plans for penstocks that have only one egress 

point provide for alternative escape routes and/or refuge chambers. 

e. Ensure the implementation of a written confined space rescue preplan for 

each designated permit space. Address staging and methods of rescue for 

each designated permit space including whether a rescue team is required 

to standby outside the space. Require that confined space rescue teams be 

standing by at the permit spaces where the hazards pose an immediate 

threat to life or health including the hazard of a potential flammable 

atmosphere. 

RPI Coating, Inc.

2008-01-I-CO-R14 Based on the findings and conclusions of this report, hire a certified safety 

professional to conduct periodic safety audits at your worksites. At a minimum, 

assess safety training, confined space safety, safe handling of flammables, 

emergency response, rescue, and fire prevention.

2008-01-I-CO-R15 Ensure that all journeyman painters have received safety training equivalent in 

content to that covered in the Joint Apprenticeship program. At a minimum,

address confined space safety, safe handling of flammables, emergency response 

and rescue, and fire prevention.
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The Society for Protective Coatings (SSPC) 2008-01-I-CO-R16

See below for recommendations text.

American Public Power Association (APPA) 2008-01-I-CO-R17

Publish safety guidance addressing the hazards and controls for using hazardous materials including 

flammables in confined spaces and the unique hazards of penstocks. At a minimum

a. In controlling hazards in confined spaces, implement a hierarchy of 

controls by first attempting to eliminate hazards or substitute with a less 

hazardous material(s) or method(s). Examples include performing work 

outside of a confined space where reasonably practicable or substituting 

a flammable material with a non-flammable one. 

b. Establish a maximum permissible percentage substantially below the 

LEL for safe entry and occupancy of permit-required confined spaces.

c. Recommend that confined spaces that are large, or part of a continuous 

system such as a penstock, always be managed as permit-required as 

defined in the OSHA Confined Space Standard, and that such spaces 

always be monitored for hazardous atmospheres both prior to entry and 

continuously in areas where work is being performed.

d. Ensure that evacuation plans for penstocks that have only one egress 

point provide for alternative escape routes or refuge chambers.

e. Provide guidance for implementing a written confined space rescue plan. 

Address staging and methods of rescue for each designated permit space 

including whether a rescue team is required to stand by outside the space. 

Require that confined space rescue teams be standing by at the permit 
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spaces where the hazards pose an immediate threat to life or health,

including the hazard of a potential flammable atmosphere.

Southern California Painting and Drywall Industries Joint Apprenticeship and 

Training Committee

2008-01-I-CO-R18 Require that all journeyman painters who are employees and/or members have 

received safety training equivalent in content to that covered in the Joint 

Apprenticeship program. At a minimum, address confined space safety, safe 

handling of flammables, emergency response and rescue, and fire prevention.

2008-01-I-CO-R19 Include a safety knowledge and skills component to your journeyman and 

apprentice evaluation criteria.
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BY THE

U.S. Chemical Safety and Hazard Investigation Board

Rafael Moure-Eraso

Chair

John S. Bresland

Member

Mark Griffon

Member

William B. Wark

Member

William E. Wright

Member

Date of Approval August 25, 2010
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Requirements in Construction Contract Documents.

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ANSI/AIHA, 2005. ANSI/AIHA Z-10, American National Standard for Occupational Health and Safety 

Management Systems.

American Petroleum Institute (API), 2005a. Recommended Practice (RP) 2220, Contractor Safety 

Performance Process, 2

nd ed.

API, 2005b. RP 2221, Contractor and Owner Safety Program Implementation.

API, 2001a. Standard 2015, Safe Entry and Cleaning of Petroleum Storage Tanks.

API, 2001b. Recommended Practice 2016, Guidelines and Procedures for Entering and Cleaning 

Petroleum Storage Tanks. 

American Public Power Association (APPA), 2007. Safety Manual: Promoting a Safe and Injury Free 

Work Environment for Public Power, 14th ed., Washington, DC.

American Society of Civil Engineering (ASCE), 1998. Guidelines for Inspection and Monitoring of InService Penstocks.

American Society for Testing and Materials (ASTM), 2007. ASTM D4276-02, Standard Practice for 

Confined Area Entry.

―Atmospheric Pressure at Site Elevation,‖ 2004. Universal Industrial Gases, Inc., 

http://www.uigi.com/Atmos_pressure.html (accessed February 2009).

Babrauskas, V., 2003. ―Halogen Lamps,‖ Ignition Handbook, Isaquah, WA: Fire Science Publishers. 
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the pipeline deaths of 4 Inland men,‖ The Press Enterprise,

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Cabin Creek Hydroelectric Plant Final Investigation Report 8/25/2010

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APPENDIX A: INCIDENT TIMELINE

Date Time Detail

Summer 1964 Construction of upper dam and reservoir underway, as part of the Cabin Creek 

Pumped Storage Hydroelectric Project.

1967 Original coal tar-based epoxy coating applied in penstock.

September 20, 2000

- December 9, 2000

Initial inspection and evaluation of the penstock determines that the internal epoxy 

coating of the steel-lined section shows signs of deterioration, including blistering and 

cracking.

June 4, 2001

Xcel internal report on the 2000 inspection states that corrective action to repair the 

areas of deterioration must be implemented to prevent continued corrosion and 

unacceptable pitting damage.

September 25, 2001 Robison-Prezioso Bay Bridge project incident kills a private citizen.

January 4, 2002 Robison-Prezioso Bay Bridge project employee fatality incident.

2004

Xcel hires a contractor to explore the possibility of creating a permanent access to 

penstock, but the project is rejected due to insufficient time to obtain FERC approval.

RPI interstate Experience Modification Rate (EMR) is 0.93.

~ October 2004

A decision is made to recoat the penstock during the 2004 outage as a result of a 

metallurgist’s inspection, which notes that the interior liner is peeling up to the concrete 

section.

2005 RPI interstate EMR is 1.03

2006

2006 SSPC audit finds that RPI has “No documentation of craft-worker assessment.” 

RPI interstate EMR is 1.28.

January 3, 2006 The KTA-Tator Coating inspection contractor submits proposal for the penstock 

recoating project to Xcel.

November 1, 2006 Xcel reviews the existing penstock recoating plan.

October 1, 2006

Xcel conducts “Safety and Health Hazard Assessment Survey,” focusing on the 

abrasive blasting portion of the recoating project work, but not the risks of epoxy 

recoating work associated with using a solvent in a confined space.

2007

Robison-Prezioso, Inc. is renamed RPI Coating; the company is ranked the nation's 

seventh-largest specialty paint company based on revenues in 2005, according to 

Engineering News-Record.
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January 16, 2007 The KTA-Tator coating assessment contractor contracts with Xcel to inspect and report 

on the quality of RPI’s penstock re-coating work for 2007 penstock recoating project.

January 17, 2007 Xcel’s internal hazard assessment of the penstock re-lining project identifies the 

penstock as having a confined space hazard.

Spring 2007 An Xcel civil engineer identifies “major items of concern” with the penstock recoating

project, including a lack of an alternative exit.

April 2007

Xcel issues an RFP to multiple vendors to recoat the penstock. Proposal asserts that 

an Xcel project manager will be fully integrated into the contractor’s safety program. 

Only one vendor meets criteria for successful completion of the job, but the vendor’s 

cost estimate exceeds Xcel’s anticipated budget.

June 2007 First bid submissions evaluated; one company meets criteria but cost estimate is 

$450,000 over Xcel’s estimated budget; Xcel resubmits the project for additional bids.

July 11, 2007

Clear Creek County Fire Authority conducts an emergency drill at the Cabin Creek 

facility, rehearsing a fire response to the power production office facility; this drill does 

not involve the penstock or a confined space rescue.

Late July 2007

RPI and one other company meet the criteria for consideration as the potential 

recoating contractor; although the competing bidder is more technically qualified and 

RPI Coating’s safety record is poor, RPI is selected due to cost.

August 27, 2007

RPI requests a copy of Xcel’s Cabin Creek site confined space procedures from the 

penstock recoating project team leader and the Xcel Cabin Creek plant manager. Plant 

manager states information will be covered in contractor orientation. 

Late August – mid 

September 2007

RPI contractors begin arriving at the Xcel Cabin Creek site.

September 4, 2007

KTA-Tator project engineer sends review of RPI coating application plan, project 

schedule, coating application procedures, and product data sheets for epoxy materials

to the Xcel recoating project team leader.

The Xcel project scheduler provides contractor orientation with an RPI foreman and five 

contractors (of the 14 RPI employees involved in the penstock work).The orientation 

form indicates that all contractors are trained for confined space entry and that MSDSs 

have been provided to Xcel plant management. RPI notifies the Xcel scheduler that the 

contractors will be using a “ketone” solvent to clean the sprayer inside the penstock.

September 5, 2007

Xcel and RPI Coating hold a “Preconstruction Meeting” where project-specific safety 

concerns are to be identified; however, the use of flammables within a confined space 

and the need for emergency response and rescue plans are not discussed. 

Xcel identifies RPI's high EMR rate during the meeting and requires RPI to take extra 

precautions and informs RPI that Xcel’s Stop Work Policy will be enforced during the 

penstock recoating project. 

September 4-9, 

2007 The upper reservoir is dewatered.
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September 10, 2007

An instructor from Southern California Painting and Drywall Industries (SCPDI) District 

36 Training Center conducts a six-hour safety refresher training session pertaining to 

OSHA-required topics at the Xcel Cabin Creek site for nine of the 14 RPI industrial 

painters at the request of RPI’s safety director. This training consists of watching safety 

videos on each topic and multiple-choice exams on the information; the training is 

general in nature and not tailored to all site-specific safety risks of the penstock work.

September 11-

October 2, 2007

A number of confined space entry permits and air monitoring logs are completed by 

RPI that indicate that continuous air monitoring is required inside the penstock.

Logs reveal that KTA-Tator and Xcel employees entered the penstock on several 

occasions to inspect and/or review RPI Coating’s work progress.

September 12, 2007

110 gallons of MEK (two 55-gallon drums) delivered to Cabin Creek site.

RPI conducted a test spray with the epoxy and MEK at Cabin Creek site; the Xcel 

principle engineer was present during this test spray. 

September 15, 2007

RPI reports trouble with 480 volt power feed to equipment in the penstock. Xcel

employees enter the penstock to troubleshoot the electrical equipment. Incorrect wiring 

is modified. 

September 16, 2007

Entry into the penstock is delayed 2 hours due to high carbon monoxide (CO) levels.

RPI experiences additional electrical service problems inside penstock.

Foreman rewires an electrical spider box in the penstock for RPI Coating.

September 19, 2007 Xcel Cabin Creek personnel leave high bay fans on to ventilate errant CO from coming 

down penstock to hydroelectric plant’s substation lower level.

September 21, 2007 RPI Coating begins sandblasting inside the penstock; the company is 5 days behind its 

tight 10-week schedule.

September 22, 2007

The Xcel Penstock Reline Project Manager observes RPI Coating conducting abrasive 

blasting inside the penstock and notes: “Work conditions inside the penstock are highly 

hazardous on many levels. In the best of conditions, the coating removal is dirty, nasty 

work.” 

KTA-Tator conducts an initial pre-job hazard assessment of the penstock, noting that 

the MSDSs for all coatings and solvents used in the project are available. Inspector 

also notes that RPI and the Xcel penstock recoating project manager were advised on 

the MSDSs.

September 26, 2007

Xcel employees enter the penstock to perform welding on weep holes to stop leaks. 

The KTA-Tator inspector conducts a “Task Summary: Coating Observation Hold 

Points” inspection of the penstock interior. Inspection identifies the use of thinner as 

part of the coating materials mixing and pre-application process, and documents the 

necessity of using thinner/solvent to flush the sprayer system equipment (including 

hoses, nozzles, and the sprayer itself).
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October 1, 2007 8:00 AM Xcel personnel conduct a safety evaluation of RPI’s sandblasting work inside penstock; 

no unsatisfactory items are noted.

~12:00 PM

An Xcel welder enters with the RPI Coating foreman to begin welding around the 

leaking seep hole/cap in the penstock. The welder does not sign into the log book at 

the penstock’s entrance.

October 2, 2007 Morning of 

Sand-blasting activities, including hand sanding and grinding of the walls, are

completed. RPI employees began the preparatory steps for applying the new coating 

onto the penstock interior. No special precautions are taken beyond those in place prior 

to starting the sandblasting operation.

8:00 AM Xcel welder completes welding job around the leaking seep hole/cap in the penstock.

1:10 PM

RPI project supervisor and KTA-Tator inspector leave for lunch.

RPI employees continue attempts to apply epoxy to the first 12-15 feet of the 

penstock’s interior, but difficulties with the sprayer and epoxy mixture prevent 

satisfactory application.

~1:55 PM

A flash fire ignites at the sprayer in the immediate vicinity of the base hopper 

while the contractors flush the system with MEK solvent. This rapid fire catches 

one contractor’s sleeve on fire and quickly engulfs a number of buckets of 

solvent located on and around the scaffold of the epoxy sprayer.

1:59 PM A worker rapidly exits from the penstock access door and runs to notify the Xcel control 

board operator about the fire in the penstock.

~2:00 PM The Xcel employees at upper reservoir mushroom hear a “whoosh,” followed by yelling, 

but what is being said is unintelligible.

2:03 PM Clear Creek County dispatch receives a 9-1-1 call from the Xcel control board operator 

regarding the fire and initiates emergency response.

2:11 PM The Clear Creek County Sheriff's officers’ response vehicle arrives at the Cabin Creek 

site.

2:20 PM Xcel operator log book documents: “Emergency services w/o confined space fire 

training arrived. They have summoned a Denver team." 

2:22 PM Additional emergency responders from various districts/units arrive at Cabin Creek site.

2:25 PM West Metro Rescue asked to respond to Cabin Creek site.

2:30 PM

An RPI contractor retrieves and gives the MSDSs to the Georgetown Police 

Department.

Henderson Mine Rescue team asked to respond to Cabin Creek site.

~2:45 PM Final radio communication from the trapped workers is received by emergency 

responders and co-workers.
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135

2:47 PM

A small group of responders and an RPI employee enter the penstock through the 

access door, travel up the penstock, but exit shortly thereafter due to the thick black 

smoke conditions.

~3:00-3:15 

pm

Xcel employees at the upper reservoir mushroom intake report seeing ash and flecks of 

burned material come out of the penstock.

3:15 PM SCBA oxygen tanks are dropped into mushroom upper end of penstock.

3:25 PM Residual smoke evident from penstock access door.

3:30:37 PM A growing smoke cloud is evident around the penstock access door.

3:40 PM West Metro Fire Rescue arrives at Cabin Creek.

3:54 PM A cloud of smoke remains evident in front of the penstock access door.

4:10 PM Henderson Mine Rescue arrives at Cabin Creek

4:45 PM Emergency responders wearing SCBA enter the penstock 

5:35 PM Emergency responders on site receive the first order from Incident Command to 

fight/extinguish the fire; Henderson Mine team to enter.

5:45 PM Henderson Mine team enters the penstock through the access door to check air quality, 

size up the fire, and locate/rescue the trapped contractors.

~9:00 PM Xcel personnel allowed back into the Cabin Creek substation building, as air monitoring 

results are found to be at safe levels.

October 3, 2007 2:00 PM Fatally injured workers are removed from the penstock.

8:00 PM The incident scene is released back to Xcel.
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APPENDIX B: REGULATORY HISTORY OF RPI COATING, INC.

OSHA Inspection and Citation History

Robison-Prezioso Inc. (RPI Coating, Inc.)

5/27/88 - 12/31/2008

Date Inspection 

Number Location State Inspection Type Emphasis Program Citation Summary Initial Penalty

Final 

Penalty Resolution

10/7/2008 312279870 Overton NV Planned - Safety OSHA 300 log errors $0 $0 Closed

5/14/2008 311643977 Jean NV Referral - Health None Closed

11/5/2007 311634307 Las Vegas NV Compliant - Health Special - Construction None $0 $0 Closed

10/2/2007 310470034

Georgetown

CO

Accident - Safety; 5 

fatalities

National - Lead; 

Special - Electrical; 

Special - Fall from 

Height; Special - Lead; 

Special - Powered 

Industrial

Working surfaces; flammable liquids; 

respirators; confined space; welding; 

electrical wiring; hazard communication $845,100 

Contested

12/29/2005 125529636 Santa Rosa CA Planned - Safety Special - Construction No ROPS or seatbelt installed on 

equipment $150 $150 Closed

10/13/2005 110569803

Davis Monthan 

AFB AZ

Program Related1-

Safety

No body belt worn on vehicle-mounted 

rotating work platform $1,375 $1,375 

Formal 

Settlement 

Agreement

(FSA); Closed

 

1 A Program Related inspection is one where OSHA conducted an unannounced programmed inspection at an establishment and also inspected RPI, who was 

working at the establishment as a contractor.
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OSHA Inspection and Citation History

Robison-Prezioso Inc. (RPI Coating, Inc.)

5/27/88 - 12/31/2008

Date Inspection 

Number Location State Inspection Type Emphasis Program Citation Summary Initial Penalty

Final 

Penalty Resolution

10/5/2005 125529289

Santa Rosa

CA

Planned - Safety Special - Construction Flaggers not used at a construction site 

when warning signs and barricades 

could not be used to control traffic

$150 $150 

Closed

9/27/2002 305639262 Vantage Bridge 

I-90 WA Complaint - Health None $0 $0 Closed

9/23/2002 305551491 Vantage Bridge 

I-90 WA Planned - Safety Local - Construction No written fall protection work plan; No fall restraints/fall arrest systems; $600 $600 State Decision

5/10/2002 300891090

San Francisco

CA

Complaint - Health National - Lead; 

Special - Construction

Cadmium - Improper removal and 

storage practices

$13,500 $280 

FSA; 24 

citations 

deleted; 

closed

1/4/2002 300890555

San Francisco

CA

Accident - Safety; 1 

fatal; 4 hospitalized

Improper scaffold design; Rated load 

capacity exceeded on suspended 

scaffold; Platform on suspended scaffold 

not wide scaffold not wide enough or 

missing a guardrail; Improper erection or 

dismantling of scaffolds; Scaffold 

overloaded

$41,400 $41,400 Open

9/25/2001 300890100

San Francisco

CA

Accident - Safety Special - Construction Framed panels not securely anchored, 

guyed, or braced; Machinery and 

equipment components not designed, 

secured, or covered to minimize hazards 

caused by breakage, release of 

mechanical energy (e.g., broken 

$18,000 $18,000 Open
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138

OSHA Inspection and Citation History

Robison-Prezioso Inc. (RPI Coating, Inc.)

5/27/88 - 12/31/2008

Date Inspection 

Number Location State Inspection Type Emphasis Program Citation Summary Initial Penalty

Final 

Penalty Resolution

springs), or loosening and falling

6/19/2001 304706450 Cape 

Canaveral AFS FL Program Related -Safety

Local - Fall, FLCare; 

Special - Construction, 

Construction Fatalities

No medical services/first aid available; 

Unsafe abrasive blasting respirators; 

Flammable liquid dispensing units 

not protected against collision 

damage; “No smoking” signs were 

not posted in flammable liquid areas; 

Spinner knobs were attached on 

steering wheels of equipment; Industrial 

truck did not meet ANSI standard 

requirements 

$9,375 $5,250 FSA; Closed

4/23/2001 304422132 Henderson NV Planned - Safety Special - Construction None $0 $0 Closed

4/23/2001 304425416 Henderson NV Planned - Health Special - Construction None $0 $0 Closed

3/20/2001 126030634 Coalinga CA Accident - Safety; 1 

hospitalized

Injury not immediately reported to CalOSHA; Forklift operating rules not 

enforced

$935 $935 

Closed
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OSHA Inspection and Citation History

Robison-Prezioso Inc. (RPI Coating, Inc.)

5/27/88 - 12/31/2008

Date Inspection 

Number Location State Inspection Type Emphasis Program Citation Summary Initial Penalty

Final 

Penalty Resolution

3/7/2001 125637058 San Francisco CA Planned - Health National - Lead; 

Special - Construction

Cadmium - No regulated area or 

demarcation, no monitoring, prohibited 

activities conducted, no medical for 

respirator use, torn PPE not replaced; 

Machinery not maintained in safe 

condition; Separate shower facilities not 

available for females; Safety glasses 

interfere with respirator; Compressed 

gas cylinder not secured while being 

transported; Pinch points on machinery 

not guarded

$83,925 $20,250 

FSA; 19 

violations 

deleted; open

2/27/2001 125619239 San Francisco CA Accident - Safety; 1 

hospitalized

Ramps/Runways not 20-inches wide; 

Metal scaffolds - Railings and planks not 

secured; Improper anchorages for 

personal fall protection equipment

$26,100 $18,000 

FSA; One 

item deleted; 

Closed

10/11/2000 300888401

Bay Bridge -

Lower Deck, 

San Francisco

CA Accident - Safety None $0 $0 Closed

12/17/1999 120266846 Pasadena CA Complaint - Health Local – Regulated 

carcingen None $0 $0 Closed

5/28/1999 302528437

Spring 

Mountain 

Overpass, Las 

Vegas

NV Complaint - Safety None $0 $0 Closed
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140

OSHA Inspection and Citation History

Robison-Prezioso Inc. (RPI Coating, Inc.)

5/27/88 - 12/31/2008

Date Inspection 

Number Location State Inspection Type Emphasis Program Citation Summary Initial Penalty

Final 

Penalty Resolution

3/2/1999 119737997

Yeruba Buena 

Island, San 

Francisco

CA Planned - Safety

Local - Regionp12

None $0 $0 Closed

12/28/1998 11967461

Yeruba Buena 

Island, San 

Francisco

CA Planned - Health

Cadmium - No initial monitoring; 

Respirators not worn; Torn PPE not 

replaced; Fall protection - Positioning 

systems not used

$2,495 $1,685 FSA; Closed

10/13/1998 302524384 Las Vegas NV Planned - Safety

More than 25 gallons of flammable or 

combustible liquids stored in a room 

outside of an approved storage 

cabinet; No portable fire extinguisher, 

having a rating of not less than 20-B 

units, located outside of, but not 

more than 10 feet from, the door 

opening into any room used for 

storage of more than 60 gallons of 

flammable or combustible liquids; 

Flammable liquids were used where 

there were open flames or other 

sources of ignition within 50 feet of 

the operation

$375 $375 

Review 

Commission 

Decision

 

2 This is a code for a state of California local emphasis program.
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141

OSHA Inspection and Citation History

Robison-Prezioso Inc. (RPI Coating, Inc.)

5/27/88 - 12/31/2008

Date Inspection 

Number Location State Inspection Type Emphasis Program Citation Summary Initial Penalty

Final 

Penalty Resolution

7/15/1998 126141324 Oxnard CA UnProgrammed 

Related3- Health Cadmium $185 $185 FSA; Closed

1/8/1998 115218703 Highway 17N, 

Soap Lake WA Complaint - Health None $0 $0 Closed

5/28/1997 125658047

Los Vacqueros 

Dam, 

Brentwood

CA Planned - No 

Inspection Local-Tunnel None

5/27/1997 126207984 Santa Maria CA Accident - Safety; 1 

hospitalized

Improper portable wooden ladders; 

Injuries not immediately reported; no 

Injury and Illness Prevention Program

$150 $150 Closed

5/23/1997 126053537 Los Angeles CA Complaint - Health No Injury and Illness Prevention 

Program $185 $185 Closed

1/17/1997 115236564 Highway 17N, 

Soap Lake WA

Complaint - No 

Inspection/Process 

Inactive

None

 

3 An UnProgrammed Related inspection is one where OSHA was conducting a fatality, compliant, or referral inspection at an establishment and also inspected 

RPI, who was working at the establishment as a contractor.
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OSHA Inspection and Citation History

Robison-Prezioso Inc. (RPI Coating, Inc.)

5/27/88 - 12/31/2008

Date Inspection 

Number Location State Inspection Type Emphasis Program Citation Summary Initial Penalty

Final 

Penalty Resolution

10/11/1996 119772846

Los Vacqueros 

Dam, 

Brentwood

CA Planned - No 

Inspection Local-Tunnel None

2/5/1996 119874667 Los Angeles CA UnProgrammed 

Related - Health None $0 $0 Closed

9/26/1995 11966949 Rodeo CA UnProgrammed 

Related - Health None

5/9/1995 112130059 Carson CA Accident; 1 

hospitalized

No training on aerial lifts; Foundation soil 

not maintained in safe condition $5,525 $600 

FSA; 1 

citation 

deleted

3/10/1994 123834228 Tracey NV Planned - Safety Hazard communication - improper 

labeling, MSDS, training; no respirators $3,000 $3,000 FSA; Closed

12/1/1993 112173331 Calabasas CA UnProgrammed 

Related - Health

No monitoring for hazardous substances 

(deleted); No eyewash $900 $225 

Administrative 

Law Judge 

(ALJ)

Decision; 1 

citation 

deleted; 

Closed

4/8/1993 12386675 Las Vegas NV Planned - Safety

No bonding/grounding when 

transferring flammable liquids 

between containers; Containers not 

provided for waste rags; Improper 

$125 $125 

State 

Decision; 

Closed
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OSHA Inspection and Citation History

Robison-Prezioso Inc. (RPI Coating, Inc.)

5/27/88 - 12/31/2008

Date Inspection 

Number Location State Inspection Type Emphasis Program Citation Summary Initial Penalty

Final 

Penalty Resolution

temporary wiring; Unapproved forklift

9/24/1992 119989457 Cardiff CA Complaint - Health Improper temporary wiring, ladders, floor 

openings $2,770 $2,475 ALJ Decision; Closed

9/23/1992 119988425 Carlsbad CA Complaint - Health -

No Inspection None

8/7/1992 107108474

Alyeska 

Pipeline Marine 

Terminal, 

Valdez

AK Compliant - Safety

Improper air compressors for abrasive 

blasting; HAZCOM labeling and MSDSs; 

No first aid training; No washing 

facilities; No respirators; Temporary 

heaters too close to combustibles; 

Improper electrical wiring; No fall 

protection

$14,300 $4,054 

Informal 

Settlement; 4 

citations 

deleted; 

Closed

7/7/1992 114570963 Henderson NV Planned - Safety

Smoking not prohibited where flammable 

liquids are present; Hazard 

communication; Flammable liquids 

stored or transferred in unapproved 

containers; Respirators; Air powered 

tools

$4,650 $2,325 

Informal 

Settlement; 

Citation 

Amendments; 

Closed

6/9/1992 11566424 Phoenix AZ Complaint - Health None

6/9/1992 115561169 Phoenix AZ Complaint - Safety None
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OSHA Inspection and Citation History

Robison-Prezioso Inc. (RPI Coating, Inc.)

5/27/88 - 12/31/2008

Date Inspection 

Number Location State Inspection Type Emphasis Program Citation Summary Initial Penalty

Final 

Penalty Resolution

5/5/1992 112051784 Lancaster CA Accident; 2 

hospitalized

No head protection; Improper rolling 

platform scaffold planks and construction $2,250 $2,250 Closed

4/3/1992 111872867 Playa Del Ray CA Accident - 1 

Hospitalized Portable ladders not secured $0 $0 ALJ Decision; Closed

1/10/1992 11199040 Playa Del Ray CA UnProgrammed 

Related - Safety Personal Fall Protection not used $600 $600 ALJ Decision; Closed

10/30/1991 112088117 Carson CA Program Related -

Safety Local - Refinery Respiratory protection not used $0 $0 Closed

8/8/1991 111994851 Oakley CA UnProgrammed 

Related - Safety Safe Code of Practices not posted $0 $0 Closed

5/16/1991 112223318 Goleta CA UnProgrammed 

Related - Health Respiratory protection no used $0 $0 Closed

4/24/1991 111979316 Fountain Valley CA UnProgrammed 

Related - Safety None

4/5/1991 111869483 Playa Del Ray CA UnProgrammed

Related -Safety None

1/7/1991 112113501 Playa Del Ray CA UnProgrammed 

Related - Safety

Flammable vapors were not 

controlled; Flammable liquid containers 

not marked; No portable fire extinguisher 

outside flammable storage room; Open 

flames not prohibited in flammable liquid 

$0 $0 Closed
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OSHA Inspection and Citation History

Robison-Prezioso Inc. (RPI Coating, Inc.)

5/27/88 - 12/31/2008

Date Inspection 

Number Location State Inspection Type Emphasis Program Citation Summary Initial Penalty

Final 

Penalty Resolution

storage rooms

12/4/1990 112117767 Playa Del Ray CA UnProgrammed 

Related - Safety Improper temporary stairs $0 $0 Closed

10/26/1990 112082862 Wilmington CA Program Related -

Safety Local - Refinery Lack of suitable eye and face protection; Hazard communication $0 $0 Closed

5/27/1988 106775455 New Hall CA UnProgrammed 

Related - Safety

Respirators; PPE; Flammable liquids in 

unapproved containers $540 $540 Closed
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APPENDIX C: INVENTORY OF FLAMMABLE AND COMBUSTIBLE 

MATERIAL IN PENSTOCK

Flammable and Combustible Material in Penstock Distance from Sprayer Number of 

buckets119

One (2-gal) bucket with MEK, heavily melted at scaffolding120 Between 79 ft and 91 ft 1

Three 5-gallon buckets of epoxy/MEK mixture (~12 gallons, of which 

~5 gallons were MEK) on penstock floor, adjacent to sprayer stage

On floor, adjacent to 

sprayer

3

Three buckets of MEK (~11-12 gallons) and at least eight buckets of 

epoxy (epoxy buckets completely melted and, therefore, unable to 

determine if base or hardener; only handles survived fire) 

On stage with sprayer 11

Eight (5-gal) buckets of base; three (5-gal) additional melted buckets 

of base; one (2-gal) bucket of hardener; and indeterminate number of 

completely melted buckets

13 ft, 9 3/8 in 12+

Twelve (2-gal) buckets of hardener; indeterminate number of 

completely melted buckets 101 ft, 1 in 12+

Ten (5-gal) buckets of base; 20 (2-gal) buckets of hardener 172 ft, 11 7/8 in 30

Four (2-gal) buckets of hardener 228 ft, 3 3⁄4 in 4

Ten (5-gal) buckets of base at 500’ mark in penstock 380 ft, 3 5/16 in 10

Nineteen (5-gal) buckets of base 532 ft, 2 7/8 in 19

TOTAL NUMBER OF BUCKETS INSIDE PENSTOCK 102+

 

119 The number of buckets, instead of actual volumetric quantity, of the epoxy and MEK are provided here because a 

number of the buckets were destroyed in the fire; only the wire handles of these buckets remained post-incident. 

As a result, the CSB could not determine if the handles belongs to 2-gallon or 5-gallon buckets. 

120 The exact location of this bucket is unknown because it was moved while victims were being removed; distance 

estimate is based on CBI initial entry report that buckets were located on and under scaffolding, and knowledge 

that scaffolding was 12 feet long, adjacent to the west bulkhead.
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APPENDIX D: EVALUATION OF IGNITION SOURCES

As Section 5.2.2 explains, numerous potential ignition sources existed in the immediate area of the 

sprayer at the time of the fire. Below is a detailed analysis of each potential ignition source the CSB 

considered. Supporting evidence for each analysis is based on examination of physical evidence, 

interviews with witnesses, tests on equipment preserved from the scene as evidence, and the physical and 

chemical properties of the materials involved at the time of the incident based on local environmental 

conditions inside the penstock. In certain cases, conflicting witness statements and extensive fire damage 

to the equipment made it impossible for the CSB to determine events and/or exact equipment 

configurations just before the fire; as a result, the CSB could not positively rule out several potential 

ignition sources due to lack of evidence.

D.1 Static Ignition of Explosive MEK Vapor-Air Mixture inside 

Sprayer Base Hopper

The CSB concluded that static electricity generated while flushing MEK in the base hopper was the most 

likely source of ignition. One worker testified that he was looking into the base hopper and saw the initial 

flash of MEK near the bottom of the hopper. The worker stated that he was holding a 3/8-inch diameter 

braided nylon, non-metal reinforced, hose with a metal JIC121 swivel connector at the end, close to the 

inside wall of the metal hopper. This was about 6 inches (15 centimeters) from the top and about 1foot 

(30 centimeters) above the MEK surface. The hopper contained a 3-inch (8-centimeter) depth of MEK, or 

about one-half gallon (2 liters). The MEK was being circulated from the base hopper through the 

sprayer‘s air-driven piston pump, electric heater, piping, and hose, back into the base hopper to flush 

remaining epoxy particles from the sprayer. 

 

121 JIC stands for Joint Industrial Council, which revised specifications for these types of connectors in the 1960s.
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Assuming that the electric heater for the base hopper on the sprayer was not operating and the 

temperature of the MEK was the same temperature as the penstock122 (approximately 47-53 °F or 8-12 

°C), the CSB determined that the hydrocarbon-air mixture in the region where the journeyman painter 

was holding the swivel connector was likely near its most easily ignitable composition (Appendix E). 

Once ignited, the brightest flame would have appeared in the bottom of the base hopper where the 

hydrocarbon-air mixture was optimal for combustion. Ignition inside the base hopper would have 

produced a rapid deflagration with an outwardly directed pressure wave, thus producing a ―fireball.‖ This 

scenario matches descriptions given by the workers who saw the initial flash.

After the incident, the JIC swivel and the base hopper hose could not be located. However, the fitting on 

the other end of the base hopper hose was still attached to the valve on the sprayer. This fitting had an 

internal diameter of 0.117 inches (0.297 centimeters). In addition, remnants were found of an inner woven 

metal sheath that had belonged to the hose used to circulate MEK in the hardener hopper. The lack of a 

similar metal sheath on the base hopper hose led the CSB to conclude that the base hopper hose was most 

likely constructed from a non-conductive material, which was likely consumed by the fire.

Based on testimonial evidence that the pump was being operated with an air supply pressure of 10-15 psig 

(0.7-1.0 barg) and using the performance curves for the 56:1 King piston pump supplied by the sprayer 

manufacturer, the CSB estimated a maximum liquid flow rate of 4-5 gallons (15-19 liters) per minute 

during circulation. The maximum flow velocity of MEK through the JIC swivel was then estimated to be 

12-16 feet (3.7-4.9 meters) per second. This estimate neglects the pressure drop from the King Pump to 

the JIC swivel connector outlet by extrapolating the pump curves to ambient pressure. Frictional losses 

would have occurred in the heater, the quarter-turn valve, piping, hoses, and the JIC swivel connector 

 

122 The air temperature inside the penstock was fairly constant, as demonstrated by daily temperature readings taken 

by the KTA-Tator inspector from the beginning of the project. 
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itself. Since the MEK was being used to clean residual epoxy base resin from the system, it is plausible 

that the narrowest parts of the system (i.e., the quarter-turn valve and JIC swivel connector) could have, at 

least periodically, become partly blocked with resin. Therefore, a range of different flow velocities, up to 

a maximum of 16 feet (4.9 meters) per second, was possible during circulation, accompanied by a range 

of different pressures at the JIC swivel connector, depending on its orientation and any additional 

restrictions created by resin blockage.

The JIC swivel connector operated as a spray nozzle with pulsed flow produced by the King piston pump. 

Consequently, MEK liquid flowing through the JIC swivel connector would have broken up into droplets. 

This shearing action would have resulted in electrical charge separation with respect to the metal 

connector, leaving a net charge on the spray and an equal but opposite charge on the ungrounded JIC 

swivel connector.

The potential for static charges to accumulate on the isolated JIC swivel connector increases as the length 

of the hose increases and as the hose diameter decreases. The electrical resistance is proportional to hose 

length and inversely proportional to the hose cross-sectional area. Static charge accumulation in the 

swivel also becomes more likely as the MEK velocity through the swivel end connector increases, as the

rate of charge separation increases, and as the operation more closely resembles a spray nozzle. Provided 

the liquid breaks up into a spray, the only continuous electrical path from the JIC swivel connector to 

ground is through the column of MEK liquid in the hose. Since circulation was carried out using a King 

piston pump, pulsation spraying increases the probability of a non-continuous outlet jet. Charging may 

have been further increased if suspended epoxy particles were present in the MEK, especially if these 

particles created flow restrictions at narrow points in the valve and/or JIC swivel.

The following analysis estimates the potential ―spark energy‖ that could be stored by an isolated JIC end 

connector and demonstrates that the spark energy was sufficient to ignite the MEK vapor-air mixture 

inside the base hopper. This discussion assumes that the resistance of the hose is infinite (i.e., constructed 
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of a non-conductive material) compared to that of the column of conductive MEK contained within it; 

that the MEK was ejected as a pulsating spray jet offering no continuous conductive path to ground; and 

that the JIC swivel connector was held close to the hopper wall creating a potential spark gap of a few 

millimeters:

The CSB calculated that the Minimum Ignition Energy (MIE) of an optimum MEK vapor-air 

mixture under penstock conditions to be about 0.5 mJ (Appendix E).

Although the capacitance of the isolated JIC swivel end connector might be only 3-5 pico 

Farads (pF), which is typical for a small metal object, this would have increased several-fold 

by coupled capacitance with both the hopper wall and journeyman painter‘s gloved hand. The 

estimated range of capacitance (―C‖) is 7-15 pF, although larger values are possible.

123

Using the formula W = 1⁄2(CV2) to describe the energy of charged capacitors, where W is the 

stored energy (Joules), C is the estimated capacitance (Farads), and V is the spark voltage 

(Volts), the voltage required to yield an incendiary spark of 0.5 mJ is in the range 8,160-

12,000 volts.

The resistance to ground (R) via the column of conductive MEK contained within the hose is 

determined by the formula R = ρL/A, where ρ is the resistivity of MEK (approximately 1 x 

105ohm-meters); L is the length of the hose (7.0 feet or 2.1 meters); and A is the internal 

cross sectional area of the hose (approximately 31.7 mm2or 3.17 x 10-5 m

2

). If these values 

are substituted, the resistance to ground via the hose is approximately 6.6 x 109ohms (or on 

the order of 1010 ohms). 

 

123 An experimental simulation would be needed to obtain a more accurate value.
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Using Ohm‘s Law (I = V/R), where I is the charging current (Ampere); V is the required 

voltage of the isolated end connector (V = 8,160-12,000 volts); and R is the ground resistance 

through the MEK in the hose (6.6 x 109ohms), the required charging current is in the range 

of 1.2-1.8 microamperes (μA). This is the charging current needed to support a voltage of 

8,160-12,000 volts on the swivel connector given the leakage resistance of 6.6 x 109ohms 

back to ground through the MEK in the hose.

The estimated voltage of 8,160-12,000 volts could have produced a spark several millimeters 

long. Spark energies of 0.5 mJ are very small (roughly 1 percent of an automobile spark plug) 

and unlikely to be observed, even if a succession of such sparks were to occur.

A circuit containing a resistor and capacitor is called an ―RC‖ circuit. In this type of a circuit, 

current varies with time. The RC time constant of the JIC swivel is about 0.1 seconds—this 

is the product of resistance to ground (on the order of 1010 ohm) and capacitance (on the order 

of 10-11 F). The connector would be capable of charging to its maximum voltage in about five 

time constants, or one-half second. Sparks could therefore have occurred on a frequency of 

about two per second given these assumptions. Incendiary sparking would have been 

prevented by gaps much larger than a few millimeters or by a continuous stream of liquid 

from the swivel to the wall. The worst case (most frequent sparking) is for the liquid to 

continuously break up into spray and the swivel to be held about 0.12 inches (3 millimeters) 

from the hopper wall and spraying downwards. This is consistent with journeyman painter‘s 

testimony of how the hose was positioned to minimize splashing the MEK inside the base 

hopper.

High-velocity MEK spraying through an isolated JIC swivel connector (i.e., ―nozzle‖) with a charging 

current of 1.2-1.8 μA could have accumulated sufficient stored energy to produce a series of incendiary 

sparks capable of igniting the MEK vapor-air mixture (i.e., having at least 0.5 mJ energy). The ignition
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probability would have been greatly increased by the large number of sparks possible during circulation, 

plus the variety of charging conditions, spark gap geometries, and mixture compositions involved. 

Although the journeyman painter was not electrically grounded, the CSB considers it unlikely that static 

ignition occurred from a ―doorknob type‖ spark between the journeyman painter and the sprayer. The 

CSB also considers it unlikely that electrical charging of the journeyman painter‘s Tyvek®coveralls124

could have resulted in brush static discharges because evidence indicates that he was essentially stationary

on the sprayer platform during the circulation operation. However, the painter might have become 

charged while holding the circulation swivel nozzle, which is considered a variation of this ignition 

source scenario. Had the painter‘s glove had a hole, notably in the thumb or index finger holding the 

nozzle, he could have become charged to many kilovolts while the nozzle was not contacting the hopper 

wall. This would have allowed a spark to subsequently occur once the nozzle approached the hopper wall. 

Assuming his capacitance was 200 pF,125 an incendiary spark would require a voltage of 2.2 kV and a 

charging current of about 0.33 μA. Accordingly, there is less than an order-of-magnitude reduction in the 

charging current requirement to give an incendiary static spark and this variation has little practical 

importance.

Lundquist et al. (1975) observed charging currents up to about 6 μA during airless paint spraying of 

conductive liquids. Although the MEK circulation operation was being carried out at much lower 

pressures and with a larger nozzle diameter than those used for airless paint spraying, the Lundquist et al.

work shows that conductive liquids such as alcohols produce higher charging currents than less 

conductive liquids and that larger diameter nozzles and higher pressures (i.e., higher liquid velocities) 

produce higher charging currents. Their article implies that charging currents vary widely with conditions, 

 

124 The manufacturer of Tyvek coveralls cautions users against wearing this type of protective clothing in flammable 

or explosive atmospheres as doing so can generate static.

125 200 pF is frequently used as an average value for the capacitance of a person (Britton, 1999, p. 44).
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and overall, supports the static charging scenario, although the magnitude of the charging current would 

need to be resolved experimentally. The need for proper grounding of paint spray nozzles is stressed in 

the Lundquist article. In addition, NFPA 77 (2007), the operating manual for the sprayer, and even RPI‘s

safety program, contain safety warnings about proper grounding of equipment and the need to use 

conductive hoses.

D.2 Stray Current Ignition of Explosive MEK Vapor-Air Mixture inside 

the Sprayer Base Hopper

Some RPI workers‘ statements reveal that a dimming of the lights at the work area inside the penstock 

nearly coincided with the initial flash of the fire. These lights were powered from PDC 3, the power 

distribution center closest to the sprayer. PDC 3 also powered the 240-volt heaters on the pump outlets. 

During interviews with the CSB, these workers associated the dimming lights with the base heater 

coming on, but the CSB found no other evidence to support this. It can be inferred only that the voltage 

supplying the lights suddenly dropping was caused by increased power load as a result of the base heater 

turning on. The dimming lights could equally well have been caused by events outside the penstock. 

Power distribution center PDC 3 was preserved as evidence and examined closely by the CSB and other 

parties at an offsite location; no evidence of internal ignition (such as shorting) was found inside. 

However, the examination did reveal that the 240-volt power supply for the heaters was wired with a 

three, rather than a four, -prong connector. Thus, there was no ground connection in the circuit and the 

sprayer was operated with a floating neutral.126 Although the sprayer was equipped with an independent 

 

126 A floating neutral means no neutral-to-ground bond in the electrical distribution system, which causes the neutral 

conductor to ―float,‖ or lose its reference to ground. Should the loading become unbalanced or an electrical short 

occur, the phase voltages fluctuate severely. This spider box had been damaged as a result of electrical problems 

early in the recoating project and repaired by an RPI employee. This individual was not a licensed electrician and 

lacked training certifications to perform electrical work.
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grounding wire, the ground wire was not connected to any ground point when it was examined after the 

incident.

At the time of the flash, two spray hoses (one containing the base, the other the hardener) were attached to 

the sprayer, each going out to the metal mixing block. While preparing the spraying equipment inside the 

penstock, an apprentice painter stated that he saw a series of ―sparks‖ jumping from the sprayer unit to 

one of the spray hoses when he connected it with a crescent wrench, implying faulty bonding in the spray 

hose. The CSB physically examined the spray hoses after the fire. Both hoses were metal-reinforced and 

thus, should have had electrical continuity to the mixing block, although no continuity measurements 

could be made due to fire damage. These sparks may have been caused by a stray current arc between the 

floating neutral of the sprayer chassis and the grounded metal hose connector. A ground path was likely 

provided, via the metal reinforcement sheath inside the hose, to the metal mixing block lying on the steel 

tunnel floor. 

Grounding via the spray hoses to the mixing block is likely, but required the mixing block to have been in 

good electrical contact with the floor of the steel tunnel. The CSB noted that the position of the box on the 

drain pipe may have produced only intermittent contact grounding. Similarly, grounding via a spray wand 

requires electrical continuity through the mixing block out to the spray wand, which would also need to 

be in electrical contact with the steel tunnel. After the incident, the spray wands were found laying on the 

wood deck platform of the sprayer scaffold, so they were not grounded. The CSB concluded that at the 

time of the flash, the sprayer may have been grounded, but it is unlikely that the sprayer was reliably 

grounded. 

Assuming that current was flowing to ground from the floating neutral connection, different metal 

components of the sprayer would have been at slightly different voltages, depending on the impedances 

between the components. Thus, a change in load on the 240-volt supply, caused by a sudden voltage drop 

at PDC 3 (resulting in the observed dimming of the lights), may have produced a change in the floating 
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neutral voltage on the sprayer chassis. The outcome may have been an electrical arc caused by a high 

voltage transient between the base hopper and the metal nozzle on the circulation hose physically held 

inside the base hopper by the journeyman painter. An arc could have occurred during contact/separation 

between the nozzle and the hopper wall. However, the use of a non-conductive hose (Section D.1) rules 

out a stray current arc as the ignition source.

D.3 Ignition of Explosive MEK Vapor-Air Mixture by Halogen Lights 

atop the Sprayer

The sprayer unit was mounted on a wheeled cart sitting on a wheeled portable tube and coupler scaffold 

positioned about 100 feet (30 meters) from a plywood bulkhead that had been erected to block off the 

steel section of penstock. The only source of illumination for the workers on the scaffold127 on which the 

sprayer was sitting was a dual fixture halogen light assembly. Based on examination of physical 

evidence128 and employee statements, the CSB determined that the halogen light assembly was placed on 

top of the sprayer pumps. Each halogen light fixture contained two 300-watt halogen bulbs. The CSB

concluded that neither light had been equipped with a glass lens; witness testimony substaintiated the lack 

of glass lenses and insufficient glass residue was found in the area after the fire to account for them.

129

The lamps were swivel-mounted on an assembly and could be oriented to point down. The base and 

hardener hoppers were situated below and to either side of the sprayer, with the top of each hopper 

approximately 25 inches (64 centimeters) from the nearest bulb, depending on the lamp orientation.

As worker statements (Section D.1) place the initial flash of the MEK vapor-air mixture inside the base 

hopper, ignition of a flammable (i.e., greater than LEL) MEK vapor-air mixture in the atmosphere by hot 

 

127 A second scaffold, positioned near the west bulkhead, had explosion-proof lights mounted to it to provide 

illumination for the two painters applying the epoxy to the penstock walls.

128 The charred and melted remains of the halogen light were found on top of the sprayer pumps after the incident. 

129 The only remains of glass found in the fire debris were identified as coming from the sprayer control panel.
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halogen lights, followed by an unobserved flashback into the base hopper, is possible, but considered 

unlikely. One of the experienced painting contractors told the CSB that the explosion-proof light on the 

scaffold dimmed, which he caught out of the corner of his eye while looking down primarily into the base 

hopper to ensure that the MEK being dispensed from the hose was not splashing – and then he saw the 

flash inside the base hopper. During this short period of distraction, it may not have been possible for the 

contractor to discern flashback from an ignition source outside the hopper. Flashback of a lean flame 

would have occurred in just a few seconds, and the flame would likely have been bluish. However, the 

CSB considers it unlikely that the contractor would not have seen the flashback from the location of the 

halogen lamps. 

As discussed in Section D.1, it is also unlikely that an optimum vapor-air mixture (approximately 5.5 

volume percent MEK) would have existed at the elevation of the halogen lights unless the base heater was 

operating. It is possible that a flammable mixture (>1.8 volume percent MEK) migrated by convection to 

the location of the halogen lights, if air ventilation was minimal, but a mixture near the LEL would have 

been more difficult to ignite. The work area was provided with forced, clean air ventilation conveyed 

through a 20-inch (51-centimeter) diameter plastic duct, magnetically attached to the metal wall of the 

penstock near the floor. It is unknown whether there was any appreciable air movement in the zone 

between the hoppers and halogen lights. The lights were located approximately at the axis of the 12-foot 

(3.7-meter) diameter tunnel. Assuming the air flow from the duct was directed toward the bulkhead at the 

time of the incident, the flow velocity back toward the tunnel entry would have been slow; the average 

upstream velocity in the penstock would be reduced by a factor of approximately 52 relative to the duct 

outlet velocity. Air velocity would have been highly variable across the tunnel at the location of the 

sprayer unit, and additional evidence suggests that a stagnation region may have existed on the upstream 

side of the unit. After using MEK to clean the spray wands on the scaffold near the west bulkhead, one of 

the two contractors at the bulkhead left the work area to get a fan due to the buildup of MEK ―fumes.‖ He 
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told the CSB that, as he squeezed past the scaffold holding the sprayer, there was ―no air movement at 

all‖ in the vicinity of the sprayer.

Since the MEK was being sprayed into the hopper at about 12-16 feet (3.7-4.9 meters) per second, it is 

possible that some liquid mist would have migrated toward the lamps by convection, increasing the 

overall fuel concentration and/or that some splashing of coarse droplets occurred (Section D.3.3).

However, ignition of the MEK vapor-air mixture at the halogen lamps would have produced an 

unconfined flash fire centered at the contractor‘s head, rather than a deflagration inside the base hopper

that propagated toward him.

While an eyewitness statement indicates that the base heater was turned off, this would not rule out the 

possibility of a sudden catastrophic failure of the base heater thermostat. If the 3.4 kW electric heater did 

come on, causing the observed dimming of the lights, the MEK temperature could have increased very 

rapidly. A malfunctioning thermostat may have led to unregulated heating; the set point of 95 oF (35 °C) 

for the base epoxy corresponded to a level of 5.5 on the thermostat dial, which had a scale of 1-9. Under 

penstock conditions, MEK boils at 154 oF (68 °C). Only a small volume of MEK was in the lines between 

the heater and the end of the hose. It is plausible that this volume was heated sufficiently to convect 

―easily ignitable‖ concentrations of vapor up to the halogen lights. For this to occur, the entire volume of 

MEK in the hopper would not have had to have been heated to the same temperature, since heated liquid 

would have been sprayed over a large area inside the hopper, creating a large surface for evaporation. 

However, this scenario represents a great deal of inference from the fact that the lights dimmed just before 

the flash and is inconsistent with eyewitness accounts that the initial flash was inside the base hopper. 

Since the thermostat was destroyed by the fire, the CSB cannot rule out the possibility that the thermostat 

failed catastrophically.

D.3.1 Ignition Caused by Halogen Lamps 

The CSB also evaluated four distinct sub-cases involving ignition by halogen lamps.
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D.3.1.1 Ignition Caused by Halogen Bulb Breakage

Halogen bulbs can break spontaneously and explode, due to the pressurized gas inside. Bulb breakage can 

be caused by contamination of the quartz surface, such as by a fingerprint, or via halide migration 

(Babrauskas, 2003). The internal filament of a halogen bulb can operate at 5,072 °F (2,800 oC) with 

somewhat lower temperatures on the support. The inside bulb wall temperature may be around 1,382 °F 

(750 oC) (Cayless & Marsden, 1983). These temperatures certainly would have been capable of igniting 

an explosive MEK vapor-air mixture. In the current case, bulb breakage might have been attributed to 

excessive vibration from the pumps or impact of MEK droplets sprayed from the hoppers. A portion of a 

hot filament from a bulb could have even fallen into the base hopper. However, the CSB ruled out 

halogen bulb breakage as a potential ignition source, when intact bulbs from both halogen lamp fixtures 

were found still mounted in their ceramic housings on top of the sprayer after the fire. All the bulbs were 

covered in soot, but that can be attributed to rich combustion of MEK during the fire.

D.3.1.2 Ignition by Bulb Terminal Arcing

In this scenario, a loose electrical connection at one end of a halogen bulb would periodically arc at the 

spring contact fitting. This arcing could be exacerbated by vibration from the pump fixture on which the 

lamps were positioned. It is unlikely a standard torque was applied to the mounting plates, so these might 

also have been subject to excessive vibration.

If the lamp prongs were made from hard tungsten or tungsten alloy, evidence of arcing (local melting or 

pitting) is more likely to be found on the spring contacts in the ceramic connectors. The spring contacts 

have a much lower melting point than the lamp prongs, assuming they are made of brass or steel. While 

arcing at the bulb terminals was not specifically investigated, visual inspection of these terminals did not 

reveal arcing patterns.
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D.3.1.3 Ignition by Hotspot on Bulb

In a published account describing a vapor ignition by a 300-watt halogen bulb involving gasoline vapor 

(Babrauskas, 2003), violent impact caused the filament to move, which created an external hotspot on the 

quartz envelope without bulb breakage. In the absence of hotspots, gasoline vapor ignition did not occur. 

Most gasoline listed in NFPA 325 (NFPA, (out of print)) have roughly the same autoignition temperature 

as MEK. No violent impact occurred in the penstock; however, a hotspot could have developed via 

impact of coarse droplets from the base hopper.

If a droplet of MEK containing dissolved ―base‖ resin were splashed onto the hot bulb region, the result 

could have been formation of a transient hotspot on or near the bulb. The nominal 1,832 °F (1,000 oC) 

hotspot would be created as residual epoxy resin decomposed and combusted either as a glowing ember 

or small flame.

Upon impact of an MEK-based mixture on a hot surface at approximately 932 °F (500 oC) or more, the 

MEK solvent will immediately evaporate. If the MEK vapor does not ignite first, the residual base might 

decompose and combust either as a glowing hotspot or small flame, which would create very high local 

temperatures commensurate with MEK‘s lower limit flame temperature of about 2,192 °F (1,200 oC). It is 

well known that the hotspot ignition temperature of ignitable gas mixtures is a strong function of hotspot 

size and contact time, although the ignition phenomenon is complex. At temperatures close to the lower 

limit flame temperature, hotspots on the order of 1 millimeter in diameter can cause almost immediate 

ignition of optimum vapor-air mixtures. As the halogen bulbs were covered by soot during the fire, the 

CSB cannot determine if a hotspot occurred on one or more of the bulbs.

D.3.1.4 Autoignition of Heated MEK Vapor Volume

A review of the literature shows that the surface temperature of individual 300-watt halogen bulbs in 

torchiere lamps is about 968 oF (520 oC) (CPSC, 1996); higher values approaching 1,100 oF (593 oC) have 

also been reported. The temperature varies with bulb diameter, design, and degree of confinement. The 
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160

halogen lights had top reflectors and should have achieved higher temperatures than torchiere lamps, 

which are open at the top and lose heat by free convection. 

The halogen lamp fixtures used in the penstock each contained two closely spaced 300-watt bulbs, so the 

bulb surface temperatures would have been greater than for single bulbs, especially on the adjacent hot 

quartz surfaces. To the CSB‘s knowledge, no relevant tests have been done on the type of halogen lamp 

fixtures involved in the MEK fire. Bulb surface temperatures could, in principle, be measured by twocolor pyrometry or other means, but no such testing was performed. 

An experiment would need to be devised and run to determine whether an MEK vapor-air mixture could 

be ignited by a hot halogen bulb fixture at optimum concentration; if not, it would rule out autoignition at 

all concentrations. Standard autoignition temperature (AIT) tests hold the vapor-air mixture for several 

minutes in a glass vessel at the test temperature; they are conservative relative to transient heating by a 

hot halogen bulb surface. The lack of confinement (i.e., lenses not present) means that transitioning from 

cool to hot flames could not have occurred via pressure increase.130 The CSB found various published 

values for the AIT of MEK, but the most reliable is reported to be 887 oF (475 oC) at one atmosphere (760 

mmHg) (Brandes, et al., 2005, pp.1-5); this corresponds to the minimum temperature for spontaneous 

ignition of the optimum MEK-air mixture in a 200 milliliter (ml) glass flask using the IEC 60079-4 test 

method. However, the low atmospheric pressure in the penstock may have elevated the MEK AIT.

The CSB concluded that the halogen bulb surface temperatures would likely need to be significantly 

higher than the AIT of MEK (at least 125-212 °F (52-100 oC) above the standard AIT) for MEK vapor 

ignition. Ignition is far more likely had a hotspot (or small flame) been created on a bulb or an adjacent 

hot surface.

 

130 MEK is subject to forming cool flames, a phenomenon that can result in a range of reported AITs.
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D.4 Hot Surface Ignition by the Sprayer Heater(s)

The CSB determined that even if the sprayer base heater had been operating at full output, its surface 

temperature would be too low to create MEK vapor-air ignition. The heater was rated for a Class 1, 

Division 2 atmosphere, with a T2 (482 °F/250 oC) rating; the standard AIT of MEK is 887 °F (475 oC).

In addition, both heaters (base and hardener) were radiographed, electrically tested, and physically 

examined after the fire by an independent consultant hired by OSHA. The consultant determined that the 

heaters did not provide an ignition source for the fire, nor did they contribute to the spread of the fire.

D.5. Compression Ignition inside One of the Sprayer Piston Pumps

In theory, if an air-operated piston pump runs ―dry,‖ adiabatic compression of air plus residual vapor 

could lead to temperatures that exceed the MEK AIT. The CSB was able to rule out this potential ignition 

source, as both hoses were reportedly circulating MEK at the time of the fire. The journeyman painter

also reported a level of about 3 inches (8 centimeters) of MEK in the base hopper where the initial flash 

was observed.

131 Thus, neither piston pump could likely have been running ―dry‖ at the time of ignition.

D.6 Electrical Spark from Heater Control Box

Electrical power for the two heaters was supplied by the heater control panel. Unlike the sprayer control 

panel, which used low voltage electronics supplied from a pneumatic generator and was approved for use 

in flammable atmospheres, the heater control box was an aftermarket addition and was not rated for use in 

flammable atmospheres. Although the heater control box was severely damaged by the fire and its 

internal components were charred,132 visual examination by the CSB revealed that the incoming power to 

 

131 The CSB could not determine the amount of MEK inside the hardener hopper at the time of the incident, but 

survivor statements indicate that MEK was also being circulated in this hopper at the time of the incident. 

132 The CSB found no evidence that an internal deflagration had occurred inside the box. 
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the box was 240-volts and fuses. The heater control box was found to contain open circuits, relays, and 

other solid-state components. Consequently, the CSB determined that it was possible for an electrical 

spark generated inside this box to ignite an explosive MEK vapor-air mixture, but for the same reasons 

described in Section D.2, this ignition source is unlikely because the heater controls were not likely being 

used at the time of the incident; an explosive MEK vapor-air mixture probably did not exist outside the 

base hopper, and a spark, if it did occur, would have had to flash back into the base hopper unobserved. 

APPENDIX E: MEK FLAMMABILITY PROPERTIES AT PENSTOCK 

CONDITIONS

Flammability data, such as flashpoints and lower and upper explosive limits are typically measured at 

standard atmospheric conditions. As this incident occurred inside a penstock at an elevation of 10,050 feet 

(3,063 meters) above sea level, the CSB needed to recalculate this data to account for the effects of the 

elevation.

Using data showing changes in atmospheric pressure at various site elevations (UIG, 2004), the CSB 

calculated the atmospheric pressure at the penstock fire location to be 523 mmHg.

Next, the equilibrium vapor pressure equation is given by

EVP = exp (A + B/T + ClnT + DTE)

Obtaining constants A-E from the Design Institute for Physical Properties Research (DIPPR) database,133

the boiling point of MEK at 523 mmHg was calculated to be 154 oF (67.8 oC). This compares with the 

―normal‖ value of 175 oF (79.4 oC) at 760 mmHg (standard atmospheric pressure).

 

133 The DIPPR database stores thermophysical properties and parameters for correlations of temperature-dependent 

property models of over 1,900 components. It has been under development since 1980 and is continuously updated 

and enhanced. DIPPR is an industrial consortium, operating as part of AIChE.
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At 523 mmHg, the vapor-liquid equilibrium curve (Figure E-1) shows that the lower and upper flammable 

limits of MEK in air (1.8-11 volume percent) are attained at respective equilibrium temperatures of 3 to 

60 oF (-16 to 15 oC). Between these temperatures, MEK vapor in equilibrium with liquid, such as deep 

inside the liquid hoppers on the sprayer, is ignitable. MEK vapor becomes most easily ignitable at an 

―optimum‖ concentration of about 5.5 volume percent, attained at an equilibrium temperature of about 36

oF (2.4 oC). 

0

10

20

30

40

50

60

70

80

0 10 20 30 40 50 60 70

Equilibrium Vapor Pressure of MEK Near Liquid Surface in Base Hopper

(Penstock Estimated Ambient Pressure = 523 mmHg)

(Assumed Hopper Liquid Temperature 47-53F)

Vapor Pressure (mmHg)

Temperature (F)

MEK Concentration range = 7.6-9.2 mol%

Upper Flammable Limit = 11 mol%

Lower Flammable Limit = 1.8 mol%

NON-FLAMMABLE

Optimum (~5.5 mol%)

Figure E- 1. Equilibrium vapor pressure of MEK near liquid surface in base hopper

Although the low atmospheric pressure in the penstock (523 mmHg) has negligible effect on the 

flammable limits, it significantly increases the mole fraction of vapor in air at any given temperature;

consequently the flash point is decreased (Figure E-2). The calculated lower theoretical flash point, 

temperature limit of flammability (TLF), is -16 oC (3.4 oF). For ignition in the base hopper, this TLF 

should be more accurate than a measured flash point because of the ambient pressure and upwards flame 
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164

propagation, which occurs at lower vapor concentrations than in a standard flash point test apparatus 

(where flame propagation is downward).

Similarly, the ―upper temperature limit of flammability‖ (UFL) can be calculated. The UFL is generally 

not sensitive to pressure in the range being considered, so the corresponding MEK vapor pressure is 57.5 

mmHg to achieve 11 mole percent MEK in the vapor and the theoretical upper flammability limit (TUF) 

is found to be 15 oC (60 oF). This result shows that MEK in the penstock could be within the flammable 

range (ignitable) at all times inside a pail or hopper.

0

50

100

150

200

250

300

-20 -10 0 10 20 30 40 50

Equilibrium Vapor Pressure of Methyl Ethyl Ketone (MEK)

Vapor Pressure (mmHg)

Temperature (Celsius)

theoretical lower limit @ 523 mmHg

 (TLF) = -16 C (3F)

VP = 9.41 mmHg

theoretical upper limit @ 523 mmHg

 (TUF) = 16 C (60F)

VP = 57.5 mmHg

Figure E- 2. Theoretical MEK flammability limits at penstock conditions

With the base side pump heater not operating, the CSB determined that the circulated MEK would have 

been at 50 ± 3 oF (10 ± 2 °C). This range compares favorably with the unheated base resin temperature of 
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165

47 °F (8.3 °C) measured by the journeyman painter with a laser temperature indicator, and the air

temperature of 53 °F (12 °C) inside the penstock measured earlier that day by the KTA inspector. Hence, 

near the liquid surface in the bottom of the hopper (i.e., where the vapor-liquid equilibrium assumption is 

most applicable), the MEK vapor concentration should have been in the range of 7.6-9.1 mole percent. 

This is slightly greater than optimum concentration (approximately 5.5 mole percent), but less than the 

upper flammable limit (UFL) of 11 mole percent. To summarize, with the heater not operating, the entire 

volume of the hopper should have been within the ignitable range and capable of deflagration (i.e., rapid 

burning with the creation of an upward pressure wave).
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APPENDIX F: LOWEST MINIMUM IGNITION ENERGY AT PENSTOCK 

CONDITIONS 

Calculation of this parameter is significant with respect to static ignition sources having very small 

energies. Faulty electrical equipment is unimportant since electrical arcs should be sufficiently energetic 

to ignite MEK vapor over the entire flammable range.

Calcote, et al. (1952) reported the Lowest Minimum Ignition Energy (LMIE) of MEK as slightly below 

0.3 mJ. However, they reported the LMIE of n-pentane at about the same value, 0.28 mJ. This is higher 

than the approximately 0.24 mJ published for similar paraffin hydrocarbons such as butane and hexane 

(Lewis & von Elbe, 1961). The latter authors also reported a significantly lower value for cyclopropane, 

0.17 mJ versus the 0.22 mJ found by Calcote et al. The CSB noted that the data of Calcote et al. tend to be 

high compared with other LMIE values. Indeed, most of the Calcote et al. data were measured at 

stoichiometric composition, and only a few compounds such as MEK were tested at optimum 

composition (approximately 1.5 times stoichiometric in the case of MEK). The test method used by 

Calcote et al. usually involved electrodes with 1/8-inch hemispherical tips versus the 1/16-inch tips used 

by Lewis & von Elbe. Quenching effects presumably caused the measured values of Calcote et al. to be 

somewhat high. It has been observed that the lowest LMIEs are found with pointed electrodes at very low 

circuit capacitance. Since Calcote et al. used various test procedures, it is not clear exactly which 

procedure was used for the MEK tests. It is possible that lower values would have been found by 

optimizing the circuit capacitance. In conclusion, the LMIE of MEK was found to be about the same as npentane, whose LMIE is about 0.24 mJ. No MEK tests have been reported under truly ―optimum‖ 

conditions of spark gap geometry and circuit capacitance.

Britton‘s method (2002) uses the heat of oxidation to estimate the LMIE of CH and CHO organic 

compounds:

LMIE (mJ) = 4.0056 – 0.06231 (- HC /S) + 0.00024333 (- HC /S)2
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167

Where ( HC /S) = Heat of Oxidation (-100.07 kcal/mol for MEK)

Hence LMIE = 0.21 mJ

From the preceding discussion, the most easily ignitable composition should be about 1.5 times 

stoichiometric or 5.50 mol%.

Lowest MIE = 0.21 mJ (5.50 mol % MEK in dry air at 298 K, 1 atm)

However, the LMIE generally increases as pressure decreases. In the penstock, the ambient pressure was 

about 523 mmHg (0.69 atmospheres). By analogy with data for propane (Figure F-1), the LMIE of MEK 

at 0.69 atmospheres (523 mmHg) should be approximately 0.5 mJ. (Britton, 1999):

Figure F-1. Effect of pressure on MIE of propane in various oxygen-nitrogen mixtures

Hence, the lowest MIE for MEK is approximately 0.5 mJ (5.50 mole percent MEK in dry air at 298 K, 

0.69 atm).

0.001

0.01

0.1

1

10

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

MIE @ 0.20 atm

MIE @ 0.33 atm

MIE @ 0.50 atm

MIE @ 1.00 atm

Minimum Ignition Energy (mJ)

O2/(O2+N2)
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APPENDIX G: WORK ACTIVITIES ALLOWED IN POTENTIALLY EXPLOSIVE ATMOSPHERES

Source Industry/Personnel Citation/Reference Requirement

OSHA Permit-required confined spaces in general 

industry

1910.146(d) Entry into permit-required confined spaces above 10% of the LFL is allowed 

provided that acceptable entry conditions for flammable vapors listed on the 

permit are followed.

Appendix C

Examples of PermitRequired Confined Space 

Programs

Example 3. Workplace. Workplaces where tank cars, trucks, and trailers, dry 

bulk tanks and trailers, railroad tank cars, and similar portable tanks are 

fabricated or serviced.

Sources of hazards. In addition to the mechanical hazards arising from the 

risks that an entrant would be injured due to contact with components of the 

tank or the tools being used, the risk also exists that a worker could be injured 

by breathing fumes from welding materials or mists or vapors from materials 

used to coat the tank interior. In addition, many of these vapors and mists are 

flammable, so failure to properly ventilate a tank could lead to fire or explosion. 

Application of interior coatings/linings. Atmospheric hazards shall be 

controlled by forced air ventilation sufficient to keep the atmospheric 

concentration of flammable materials below 10% of the lower flammable limit 

(LFL) (or lower explosive limit (LEL)), whichever term is used locally). The 

appropriate respirators are provided and shall be used in addition to providing 

forced ventilation if the forced ventilation does not maintain acceptable 

respiratory conditions.

Std Interpretation letter, 

9/4/96

The permit-required confined spaces standard [29 CFR 1910.146] does not 

prohibit working in a permit-required space where the atmosphere is above 

10% of the LFL. However, once the atmosphere is above 10% of the LFL, all 

requirements of the standard must be met. The employer must identify and 

evaluate each hazard to which entering employees will be exposed. Based on 

the hazard analysis, the employer must develop and implement the means, 

procedures, and practices necessary for safe permit space entry operations. If 

the flammable atmosphere is the result of a process involving equipment, there 

may be precautions with regard to the equipment that an employer would be 

required to follow.
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Source Industry/Personnel Citation/Reference Requirement

Confined spaces using alternative entry 

provisions in general industry

1910.146(c)(5)

OSHA Directive 2.100, page 

19.

58 FR 4488

In confined spaces using alternative entry procedures, entry is permitted 

provided the concentration of the flammable substance does not exceed 50% 

of what would constitute a “hazardous atmosphere” (e.g., 5% of the LFL).

Confined and enclosed spaces and other 

dangerous atmospheres in shipyard 

employment

1915.13(b)(3) An employee may not enter a space where the concentration of flammable 

vapors or gases is equal to or greater than 10% of the LEL. Exception: An 

employee may enter for emergency rescue or for a short duration to install 

ventilation equipment necessary to start work, provided no ignition sources are 

present, the atmosphere in the space is monitored continuously, atmospheres 

at or above the upper explosive limit are maintained, and respiratory and other 

appropriate PPE and clothing are provided. 

Excavations 1926.651(g)(1)(iii) In excavation and trenches, adequate precautions shall be taken, such as 

providing ventilation, to prevent employee exposure to an atmosphere 

containing a concentration of a flammable gas in excess of 20% of the lower 

flammable limit (LFL) of the gas.

Underground construction (tunneling) 1926.800 When air monitoring shows, for 3 consecutive days, 10% or more of the LEL for 

methane or other flammable gases measured at 12 inches from the roof, face, 

floor, or walls in any underground work area, additional safety precautions are 

required. These include using more stringent ventilation requirements, using 

diesel equipment only if it is approved for use in gassy operations, posting each 

entrance with warning signs, prohibiting smoking and personal sources of 

ignition, maintaining a fire watch when hot work is performed, and suspending 

all operations in the affected area until all special requirements are met or the 

operation is declassified. Additional air monitoring is also required.

Confined spaces in construction, except for 

diving, non-sewer excavations, and 

underground construction

1926.1028 (proposed) Entry into permit-required confined spaces (PRCS) above 10% of the LFL is 

allowed provided conditions under which the authorized entrants can work 

safely are defined, including hazard levels and methods of employee 

protection. Monitoring procedures must also be in place to detect an increase in 

atmospheric hazard levels in sufficient time for the entrants to safely exit the 

PRCS in the event the ventilation system stops working.
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Source Industry/Personnel Citation/Reference Requirement

72 FR 67391 OSHA requests comment on the advisability of reconciling the difference in 

LFLs between the excavation standard in subpart P and this proposed 

standard, including which LFL (that is, 10% or 20%) should be adopted.

MSHA Underground Coal Mines 75 CFR 323 When 1.0% or more methane (20% of LEL) is present in a working place or an 

intake air course, including an air course in which a belt conveyor is located, or 

in an area where mechanized mining equipment is being installed or removed--

except intrinsically safe atmospheric monitoring systems (AMS), electrically 

powered equipment in the affected area shall be de-energized, and other 

mechanized equipment shall be shut off; changes or adjustments shall be 

made at once to the ventilation system to reduce the concentration of methane 

to less than 1.0%; and no other work shall be permitted in the affected area 

until the methane concentration is less than 1.0%. 

When 1.5% or more methane (30% of LEL) is present in a working place or an 

intake air course, including an air course in which a belt conveyor is located, or 

in an area where mechanized mining equipment is being installed or removed--

everyone except those persons referred to in §104(c) of the Act shall be 

withdrawn from the affected area and, except for intrinsically safe AMS, 

electrically powered equipment in the affected area shall be disconnected at 

the power source.

Underground Metal Non-Metal Mines 57 CFR 22231- 22238 If methane reaches 0.25% (5% of LEL) in the mine atmosphere, changes shall 

be made to improve ventilation, and MSHA shall be notified immediately.

If methane reaches 0.5% (10% of LEL) in the mine atmosphere, ventilation 

changes shall be made to reduce the level of methane. Until methane is 

reduced to less than 0.5%, electrical power shall be de-energized in affected 

areas, except power to monitoring equipment determined by MSHA to be 

intrinsically safe under 30 CFR part 18. Diesel equipment shall be shut off or 

immediately removed from the area and no other work shall be permitted in 

affected areas. 

If methane reaches 1.0% (20% of LEL) in the mine atmosphere, ventilation 

changes shall be made to reduce the methane. Until such changes are 

achieved--all persons other than competent persons necessary to make the 

ventilation changes shall be withdrawn from affected areas; electrical power 

shall be de-energized in affected areas, except power to monitoring equipment 
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Source Industry/Personnel Citation/Reference Requirement

determined by MSHA to be intrinsically safe under 30 CFR part 18; and diesel 

equipment shall be shut off or immediately removed from the area.

If methane reaches 2.0% (40% of LEL) in the mine atmosphere, all persons 

other than competent persons necessary to make ventilation changes shall be 

withdrawn from the mine until methane is reduced to less than 0.5% (10% of 

LEL). 

Environmental 

Protection Agency 

(EPA)

Personnel activities at hazardous waste sites Standard Operating Guides,

EPA, December 1984

Less than 10% of LEL, continue investigation; 

10 to 25% of LEL, continue onsite monitoring with extreme caution as higher 

levels are encountered; 

Above 25% of LEL, explosion hazard. Withdraw from area immediately.

ANSI Confined spaces at normal atmospheric 

pressure. Not applicable to underground mining, 

tunneling, caisson work, or intentionally inert 

confined spaces

Z117.1-2003

Section 6.3.2

Entry into confined space prohibited until appropriate controls are implemented 

or appropriate personal protective equipment (PPE) is provided whenever 

atmospheric testing indicates flammable levels are greater than 10% of the

LEL/LFL.

API Personnel cleaning stationary, aboveground 

atmospheric and low pressure petroleum 

storage tanks

Standard 2015-2001

Section 8.3.3.2.

Entry into tanks is prohibited when the flammable vapor-air levels are above 

10% LEL, unless there are extraordinary circumstances requiring such entries 

and employers (owners/operators and contractors) have established and 

implemented appropriate precautions and safeguards for permit required 

confined space entry.

NFPA Vessels that carry, or burn as a fuel, flammable 

or combustible liquids and vessel that carry 

compressed gases, chemicals in bulk, or other 

products capable of creating a hazardous 

condition

Standard 306 – 2003

Section 4

Compartments where flammable vapor-air levels are less than 10% of the LEL 

are marked as “Safe for Workers” or “Safe for Hot Work”. Compartments with 

vapor-air levels that exceed 10% of the LEL are marked “Enter With 

Restrictions” and can be entered only with appropriate PPE to install ventilation 

or perform emergency rescue.

Tanks or containers operating at normal 

atmospheric pressure that contain or have 

contained flammable or combustible liquids or 

other hazardous substances and related vapors 

and residues that are to be entered or cleaned

Standard 326 – 2005

Sections 6.3.2, 6.3.8, 6.3.9

All work in and around the tank or container shall be stopped immediately when 

flammable vapors in the atmosphere exceed 10% of the LFL. Source of the 

vapors located and eliminated or controlled.

When a tank or container is tested prior to the start of hot work, any indication 

of flammable gas or vapor in excess of the established allowable limits shall 

require additional ventilation, purging, re-cleaning, or further safeguarding by 
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Source Industry/Personnel Citation/Reference Requirement

one of the methods described in this standard, as specified by the qualified 

person, prior to the issuance of a hot work permit.

When testing a tank or container during hot work, any indication of flammable 

gas or vapor in excess of the established allowable limits shall require the 

immediate cancellation of the hot work permit.

Emergency/fire personnel responding to 

releases of flammable or combustible liquid, 

gas, or vapor that can migrate to a subsurface 

structure

RP 329 – 2005

Sections 5.4.5.1 – 5.4.5.3

During initial response to a reported leak, the affected area should be 

evacuated when gas or vapor concentrations are above 50% of the LFL. The 

affected area should be ventilated to remove or reduce the flammable gas or 

vapor concentration and thus reduce the fire or explosion hazard. As soon as 

the flammable gas or vapor has been reduced below 50% of the LFL, entry can 

be made to locate and eliminate the source.

Emergency/fire personnel performing rescue 

from confined spaces

Standard 1006 – 2008

Section A.7.1.1.(2)

Flammability is measured as a percentage of a material’s LEL or LFL. 

Rescuers should not enter confined spaces containing atmospheres greater 

than 10% of a material’s LEL, regardless of the PPE worn. There is no 

adequate protection for an explosion within a confined space.

NIOSH Criteria for a Recommended Standard –

Working in Confined Spaces

Publication No. 80-106 –

1987

Less than 10% of the LFL, no modification of work processes; between 10-19% 

of LFL, ventilation and protective measures; 20% of LFL or above, ventilation 

and protective measures.

International Union 

of Painters and 

Allied Trades, Joint 

Apprenticeship and 

Training Fund

Apprentice and Journeymen Painters Confined Space Entry, 

Employee Handbook and 

Facilitator Guide

(Summit Training Source, 

Inc.)

Permit Space Hazards

Flammable Gas, Vapor, or Mist

If the atmospheres contain flammable gas, vapor, or mist in excess of 10% of 

its LFL, that atmosphere is unacceptable for entry.

Pipeline 

Association for 

Public Awareness

Firefighters, law enforcement officers, 

emergency

Medical technicians and all other emergency 

Appendix B Natural Gas Escaping Inside a Building

EMERGENCY RESPONSE
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Source Industry/Personnel Citation/Reference Requirement

responders responding to pipeline incidents Monitor the atmosphere, using multiple monitors where possible

Action Criteria: 0 to 10% of the LEL - Use Extreme Caution

Action Criteria: 10% of the LEL or greater - DO NOT ENTER THE 

BUILDING

TACTICAL CONSIDERATIONS

Natural gas released inside buildings presents one of the greatest 

flammable hazards to emergency responders.

Building full of natural gas should be approached only when needed with 

extreme caution and with a minimum number of personnel. CGI reading s 

in excess of 10% LEL require evacuation of the building.

Alberta Worksite or work area Handling and Storage of 

Flammable Materials at the 

Work Site (May 2007)

OHS Code, Part 10

Work is prohibited in areas greater than 20% of the LEL, except for competent 

workers responding to emergencies

British Columbia Confined Spaces Confined Space Entrance 

Reference Manual (2007)

Section 9.5, OH&SR

Workers not allowed entry into confined spaces under any circumstances when 

the flammability is greater than 20% of the LEL. Good practice to prohibit hot 

work in atmospheres providing a reading on the flammable gas meter above 

1%. Any untested confined space is considered IDLH.

Ontario Confined Spaces Confined Spaces Guideline 

(1996)

Hot work permitted if concentration of flammable or explosive gas or vapor is 

less than 5% of LEL.

Cold work permitted if concentration of flammable or explosive gas or vapor is 

less than 10% of LEL.

Inspection permitted if concentration of flammable or explosive gas or vapor is 

less than 25% of LEL.

No entry permitted if concentration of flammable or explosive gas or vapor 

exceeds 25% of LEL.

Australia Confined Spaces AS 2865 – 1995 No entry into a confined space permitted if the concentration of the flammable 
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Source Industry/Personnel Citation/Reference Requirement

contaminant in the atmosphere exceeds 5% of the LEL.

When persons have entered a confined space and are using continuous 

monitoring, they may remain in the confined space at concentrations of 

flammable contaminant in the atmosphere of less than 10% of the LEL before 

evacuation of the confined space is necessary.

New Zealand Confined Spaces Safe Working in a Confined 

Space (no date)

Concentration of flammable contaminant in the atmosphere is 0% of the LEL if 

hot work is to be carried out, or 10% if cold work is to be varied out.

United Kingdom Shipping Industry IACS Confined Space Safe 

Practice

Section 6.3

April 2007

A space with an atmosphere with more than 1% of the LFL or LEL on a 

combustible gas indicator should not be entered.
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APPENDIX H: APPLICABLE OSHA CONFINED SPACE STANDARDS

H.1 OSHA General Industry Standards (29 CFR 1910)

The CSB reviewed OSHA safety and health regulations addressing confined space requirements 

applicable to general industry as well as those for construction. The CSB determined that OSHA general 

industry standards codified at 29 CFR 1910 apply to the penstock recoating project at the Xcel Cabin 

Creek facility based on OSHA definitions of construction versus maintenance [29 CFR 1910.12(b), 29 

CFR 1926.13(a) and 1926.32(g)]. Although the contractor (RPI) was using construction practices (e.g., 

sandblasting and coating) to physically change the power plant, the penstock was existing equipment 

(constructed in 1967) that was being refurbished by removing the old coating and applying new. 

Consequently, this work activity is classified as maintenance rather than new construction and falls under 

the OSHA general industry standards.

H.2 Electrical Power Generation (29 CFR 1910.269)

Although the CSB found that OSHA‘s electrical power generation standards apply to the Xcel Cabin 

Creek hydroelectric power plant, these standards contain no specific regulations pertaining to penstocks,

and the penstock does not meet the definition of an ―enclosed space‖ as outlined in this standard. As 

discussed in Section 2.1, the Xcel Cabin Creek facility is a pumped hydroelectric power plant that 

supplies electricity to residential customers during peak demand periods. As its purpose is to generate 

electrical power, the Xcel Cabin Creek facility is subject to the regulations of OSHA‘s general industry 

standard that apply only to electrical power generation, transmission, and distribution codified at 29 CFR 

1910.269. In fact, 29 CFR 1910.269(a)(i)(B)(2) specifically states that ―water and steam installations, 

such as penstocks, pipelines, and tanks providing a source of energy for electric generators‖ are subject to 

these standards. A review of the 1910.269 standard reveals that it contains no specific requirements for 

penstocks, but does contain specific requirements for ―enclosed spaces.‖ Subparagraph (e) outlines safe 

work practices, evaluation of potential hazards, atmospheric testing, ventilation, attendants, and rescue 
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provisions that are applicable to ―enclosed spaces.‖ However, the definition of an ―enclosed space‖ at 29 

CFR 1910.269(x) states that these spaces are ―designed for periodic employee entry under normal 

operating conditions‖; thus, the penstock cannot be classified as an ―enclosed space‖ under the 1910.269 

standard because under normal operating conditions the penstock is filled with water and employees do 

not enter. A note beneath the ―enclosed space‖ definition states that if the space meets the criteria for a 

permit-required confined space then the provisions of 29 CFR 1910.146 apply.

H.3 Permit-Required Confined Spaces (29 CFR 1910.146)

See Section 10.0, ―Regulatory and Industry Standards Analysis.‖
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APPENDIX I: CSB CONFINED SPACE INCIDENTS DATA INCLUSION 

CRITERION AND LIMITATIONS

To determine the prevalence of confined space incidents attributable to a flammable atmosphere, the CSB 

researched and identified a number of confined space incidents from various sources.

1

Incidents were 

included in the CSB database if they occurred in a confined space and resulted from a fire or explosion 

where monitoring of the atmosphere and establishing safe flammable limits could have played a role in 

preventing entry or requiring exit from the space. The CSB search included only incidents that occurred 

in what was determined to be an OSHA defined confined space. Incidents were selected if they occurred 

after April 15, 1993, and if work was being performed inside the confined space where a flammable 

atmosphere was either created by the work being conducted or present prior to entry resulted in an 

explosion or fire.

The CSB obtained a majority of these incidents by using specific search terms to query OSHA‘s IMIS

database where inspection records of OSHA investigations are recorded and categorized. The CSB‘s data 

search retrieved incidents containing the words ‖confined space‖ in the summary words, incident 

summary description, or title of the inspection report. If an incident occurred in a confined space, but the 

words ‖confined space‖ did not appear on that inspection report as a descriptor, it was not initially 

identified as an incident of interest. Only after subsequent queries into the IMIS system to identify 

incidents that contained a ―flammable atmosphere,‖ ―explosion,‖ or ―chemical fire,‖ among others, were

additional confined space incidents identified. For example, a few of our incidents did not contain the 

 

1

Sources included the NIOSH Fatality Assessment and Control Evaluation (FACE) Program reports, the OSHA 

Inspection Data from OSHA‘s Integrated Management Information System (IMIS) from 1993 to the present, 

media reports and inquiry into the Agency of Toxic Substance and Disease Registry (ATSDR), and the Hazardous 

Substances Emergency Events Surveillance (HSEES) system to determine the prevalence of incidents attributed to 

a flammable atmosphere. 
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words ‖confined space‖ but were retrieved under these search terms and found to contain OSHA confined 

space citations.

Additionally, a few of the incidents included in the CSB dataset were obtained through Internet media 

searches. These incidents were then checked in the OSHA IMIS database and matched with their 

correlating OSHA inspection number. If these media incidents contained OSHA confined space citations 

under the standard 1910.146, they were included into the CSB database. However, some incidents found 

through the media search had an OSHA inspection number but not an OSHA inspection report description 

or confined space citations indicating that the incident occurred in a confined space; thus, they were not 

included in the CSB dataset. Other OSHA IMIS incidents contained OSHA confined space citations but 

no incident summary indicating that the accident occurred in a confined space and were therefore

excluded from the dataset. Incidents were included only in the CSB dataset if the OSHA confined space 

citations were connected to the explosion or fire. As a result of incomplete or inconsistent reporting of 

confined space incidents in the OSHA IMIS system, the voluntary nature of incidents reported to NIOSH 

to generate the NIOSH Fatality Assessment and Control Evaluation (FACE) reports and the lack of 

specific confined space data in ATSDR HSEES, the CSB concluded that there is a likely undercount in 

confined space incidents that occurred in a flammable atmosphere in our data.

Confined space incidents obtained from OSHA‘s IMIS, the NIOSH FACE reports, ATSDR, and the 

media were categorized into two subgroups. Subgroup A contained incidents that matched our inclusion 

criterion, and subgroup B contained incidents that did not fully meet our inclusion criterion. Of the 105

incidents compiled by the CSB, 53 were subsequently categorized as A and determined to be a result of a 

flammable atmosphere in a confined space.
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APPENDIX J: SIMILAR RECENT CONFINED SPACE INCIDENTS 

INVOLVING FLAMMABLES INVESTIGATED BY THE CSB

Since the Xcel penstock incident, the CSB has investigated two additional confined space incidents 

involving workers who were injured or fatally wounded by an explosion or fire involving flammables in a 

confined space.

13.1.1 ConAgra Foods Processing Plant Explosion

On February 16, 2009, a North West Metal Fabricators contractor was killed while attempting welding 

repair to a 11⁄4 by 1⁄2 inch (3.2 by 1.3 centimeters) crack on a clarifier tank at a ConAgra facility in 

Boardman, Oregon. The 23-foot (7-meter) tall, 12-foot (3.7-meter) diameter tank had an open top 

structure and cone-shaped bottom covered by a metal skirt. The tank, used in a potato-washing process for 

separating dirt and debris from waste water, was classified as a permit-required confined space. 

The CSB investigators found an accumulation of approximately 14 inches (36 centimeters) of bacteriarich debris and water under the tank‘s skirting as a result of the material leaking through the crack. 

Through sample analysis, the CSB determined that bacteria in this debris and waste water likely produced 

flammable gas. When the contractor started welding, the arc generated acted as the source of ignition, 

resulting in a confined vapor explosion. Air monitors were used to detect flammable vapors near the 

entrance of the tank but were not used in the vicinity where the hot work was conducted.

13.1.2 TEPPCO Terminal Explosion 

Three contractors from C&C Welding, Inc. were fatally injured on May 12, 2009, in an explosion at the 

TEPPCO Partners LP McRae Terminal in Garner, Arkansas. The workers were using a cutting torch 

above the floating roof inside a 67,000-barrel (10,700 cubic meters) capacity gasoline storage tank when 

an internal explosion blew both the floating roof and the fixed roof off the tank. The contractors were 

preparing for the installation of a gauge pole, and at the time of the explosion were using an oxygen 

acetylene cutting torch to cut into the secondary roof of the internal floating roof of the tank. The 
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contractors were issued both a hot work permit and confined space permit to flame-cut the roof and enter 

the tank. However, an evaluation of both the hot work and confined space entry permit and policies of 

TEPPCO Partners LP and C&C Welding Inc. reveals no maximum or minimum LEL limits for work 

within confined spaces. The flame-cutting activity most likely ignited flammable vapors inside the tank.