September 2003 • NREL/SR-540-34817 

L.R. Waterland, S. Venkatesh, and S. Unnasch 

TIAX LLC 

Cupertino, California 

Safety and Performance 

Assessment of Ethanol/Diesel 

Blends (E-Diesel) 

National Renewable Energy Laboratory 

1617 Cole Boulevard 

Golden, Colorado 80401-3393 

NREL is a U.S. Department of Energy Laboratory 

Operated by Midwest Research Institute • Battelle • Bechtel 

Contract No. DE-AC36-99-GO10337 
September 2003 • NREL/SR-540-34817 

Safety and Performance 

Assessment of Ethanol/Diesel 

Blends (E-Diesel) 

L.R. Waterland, S. Venkatesh, and S. Unnasch 

TIAX LLC 

Cupertino, California 

NREL Technical Monitor: R. McCormick 

Prepared under Subcontract No. KLCI-1-31025-07 

National Renewable Energy Laboratory 

1617 Cole Boulevard 

Golden, Colorado 80401-3393 

NREL is a U.S. Department of Energy Laboratory 

Operated by Midwest Research Institute • Battelle • Bechtel 

Contract No. DE-AC36-99-GO10337 
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iii

Table of Contents 

Executive Summary .................................................................................................... ES-1 

1. Introduction........................................................................................................ 1-1 

2. FMEA Methodology.......................................................................................... 2-1 

3. Safety Assessment.............................................................................................. 3-1 

3.1 Initial FMEA Risk Ranking ................................................................... 3-3 

3.1.1 Gasoline and Diesel Ratings .................................................................. 3-3 

3.1.2 E-Diesel FMEA Rating.......................................................................... 3-8 

3.2 Post-Action Revised FMEA Safety Risk Ranking .............................. 3-11 

4. Performance Assessment ................................................................................... 4-1 

4.1 Initial FMEA Performance Impact Ranking.......................................... 4-2 

4.2 Post-Action Revised FMEA Performance Impact Ranking .................. 4-7 

5. Conclusions........................................................................................................ 5-1 

References..................................................................................................................... R-1 
iv 

List of Tables 

Table 2-1. Occurrence, Severity, and Detection Ratings........................................... 2-2 

Table 2-2. FMEA Worksheet Template .................................................................... 2-3 

Table 3-1. Properties of E-Diesel and Other Fuels (2, 7, 11, 12, 13, 14) .................. 3-1 

Table 3-2. Potential Safety Risk Failure Modes........................................................ 3-4 

Table 3-3. Safety Risk FMEA Ratings for Diesel Fuel Use...................................... 3-5 

Table 3-4. Safety Risk FMEA Ratings for Gasoline Use.......................................... 3-6 

Table 3-5. Initial Safety Risk FMEA Ratings for E-Diesel Use................................ 3-9 

Table 3-6. Revised Safety Risk FMEA Ratings for E-Diesel Use .......................... 3-12 

Table 3-7. Final Ranked Safety Risk FMEA Ratings for E-Diesel Use.................. 3-15 

Table 4-1. Properties Affecting Engine Performance of Several Fuels and Fuel 

Components (2, 3, 7, 14, 17, 18) .............................................................. 4-1 

Table 4-2. Potential Performance Failure Modes ...................................................... 4-3 

Table 4-3. Performance Risk FMEA Ratings for Diesel Fuel Use............................ 4-4 

Table 4-4. Initial Performance Risk FMEA Ratings for E-Diesel Use ..................... 4-6 

Table 4-5. Revised Performance Risk FMEA Ratings for E-Diesel Use .................. 4-9 

Table 4-6. Final Ranked Performance Risk FMEA Ratings for E-Diesel Use ....... 4-12 
ES-1

Executive Summary 

There has been a recent revival in interest in the use of ethanol-diesel fuel blends 

(E-diesel) in heavy-duty vehicles as a means to reduce petroleum dependency, increase 

renewable fuels use, and reduce vehicle emissions. At present there are five main 

providers of additive packages that allow the preparation, by splash blending, of stable 

E-diesel blends generally containing 10% to 15% ethanol. The current target market is 

use in centrally-fueled vehicle fleets. Because E-diesel does not meet all the ASTM 

specifications for diesel fuel, it probably cannot be legally sold at the retail level in most 

states. 

The major concern with the use of E-diesel derives from its flammability characteristics. 

E-diesel blends containing 10% to 15% ethanol have the vapor pressure and 

flammability limits of ethanol. This means that ethanol concentrations in enclosed 

spaces such as fuel storage and vehicle fuel tanks are flammable over the temperature 

range of 13 to 42°C, typical ambient temperatures. Thus, there are increased risks of 

fire and explosion compared to diesel fuel, or even gasoline. Other vehicle 

performance-related concerns have also been raised. These include decreased maximum 

power, increased incidence of fuel pump vapor lock, and reduced fuel pump and fuel 

injector life due to the decreased lubricity of ethanol. 

In this study, TIAX performed a failure mode and effects analysis (FMEA) to evaluate 

the relative safety risks and performance risks of E-diesel use compared to standard 

diesel fuel use. The fuel use process evaluated included the preparation, transportation, 

fleet vehicle fueling station storage, and use of E-diesel. Only the use of E-diesel fuel 

containing up to 15% ethanol in heavy-duty vehicle fleets was evaluated. 

The safety risk FMEA concluded that, without fuel system infrastructure, fueling 

station, and vehicle modifications, E-diesel use poses significantly greater risks than 

diesel fuel or even gasoline in comparable applications. All safety risks identified and 

ranked were risks of fire or explosion. The most significant safety risks are associated 

with the possibility of explosion in storage and vehicle fuel tanks, and the potential for 

spilled fuel fires resulting from traffic accidents involving fuel transportation tankers or 

fleet vehicles. However, the safety risks can be mitigated by adopting many of the 

infrastructure and vehicle modifications employed in the methanol fueled heavy-duty 

vehicle demonstration programs performed in the 1980s and early 1990s. 

Recommended actions to reduce safety risks include: 

• Equipping all fuel storage tank vents and the vehicle tank vent and fill openings 

with flame arresters designed for use with ethanol 

• Ensuring that all fuel transfer processes including vehicle fueling incorporate 

effective vapor recovery systems 

• Establishing an electrical ground connection between the vehicle and the fueling 

station fuel dispenser 

• Insuring that vehicle fuel tank level detectors are of an intrinsically safe design 
ES-2

By adopting these modifications, the relative risk of E-diesel use for most failure modes 

evaluated becomes comparable to that for gasoline and diesel fuel use in centrallyfueled vehicle fleets, the only use currently recommended for E-diesel. 

The performance FMEA for E-diesel use concluded that the loss of engine maximum 

power was the most significant adverse performance effect. This was followed by 

possible fuel pump cavitation causing vapor lock or fuel vaporization in injectors and 

potential fuel filter clogging problems. Recommended actions to address these possible 

adverse effects included: 

• Increasing the capacity of the fuel injection pump(s) on a case-by-case basis 

• Installing an electric fuel pump at the vehicle fuel tank and adding a restrictor fitting 

to the fuel return line 

• Ensuring that all fuel handing system and vehicle engine fuel system components 

are of E-diesel compatible materials 

Taking these actions returns system performance to a level comparable to that of diesel 

fuel. However, some of these actions may have unacceptable or unwarranted expense, 

or result in a requirement to re-certify the engine for emissions compliance. 
1-1

1. Introduction 

The global petroleum fuel crises in the 1970s caused considerable attention to be 

focused on the use of alternative fuels, particularly alcohol fuels. Methanol (M100) was 

looked into as an alternative diesel fuel for use in heavy-duty vehicles. Denatured 

ethanol (E95) was also used in transit buses that operated in the Midwest and as a 

replacement for M100 in transit buses during a period of high methanol prices. Blends 

of methanol and ethanol in gasoline, with focus on blends containing 85% alcohol (M85 

and E85), were evaluated as alternative light-duty vehicle fuels. A blend of 10% 

anhydrous ethanol in gasoline (E10) was commercially introduced and is still marketed. 

While ethanol readily blends with gasoline to form stable solutions at any blend ratio, 

blends of ethanol with diesel fuel (E-diesel) are less stable. Anhydrous ethanol easily 

blends with diesel fuel to form stable solutions containing up to a few tens of percent 

ethanol at warm ambient temperatures (1). However, at temperatures below about 10°C 

the blend separates into two phases for ethanol contents of 20% or higher (1, 2). There 

are two additive-based approaches to maintaining stable blends at low temperature: 

adding emulsifiers (surfactants) that produce stable emulsions or microemulsions, or 

adding cosolvents that produce stable solutions. Work in the 1980s focused on 

emulsifiers, and it was shown that E-diesel emulsions were technically acceptable fuels 

for existing diesel engines. However, the relatively high cost of ethanol production at 

the time put E-diesel at an economic disadvantage (2). 

In more recent years the economics of ethanol production have become more favorable 

compared to petroleum fuel costs. Accordingly, interest in E-diesel fuels as a means to 

reduce petroleum demand and increase renewable fuels use has once again increased. 

According to additive vendors, current approaches to preparing E-diesel blends rely 

predominantly on cosolvents, with most additive vendors targeting E-diesel blends 

containing 10 to 15% fuel grade anhydrous ethanol. These clear, stable blends can be 

prepared by splash blending, which is just pouring the components together into a tank. 

Currently there are five predominant blend additive vendors: Pure Energy Corporation 

(3), O2 Diesel (formerly AAE Technologies) (4), AKSO Nobel (5), Lubrizol (6), and 

GE Betz (formerly Betz-Dearborn) (7). The first four of these state that their additive 

package is cosolvent-based, while the Betz-Dearborn additive appears to be an 

emulsifier (8). 

In addition to the benefit of reducing petroleum dependency and increasing renewable 

fuels use, E-diesel brings the added benefits of reducing diesel particulate matter (PM) 

emissions and CO emissions from engines employing the fuel. Various evaluators have 

reported 20 to 40% PM reductions and 20 to 30% CO reductions (9). The effects of Ediesel on NOx emissions have been generally insignificant. 

The major concern with E-diesel use as an alternative fuel for heavy-duty vehicles is the 

increased safety risk posed by the increased risk of fire or explosion. Ethanol, based on 

its flash point, is a National Fire Protection Association (NFPA) Class I liquid, the same 

class as gasoline. In contrast, diesel fuel is a Class II liquid. E-diesel blends containing 

10% or more ethanol have the flash point of ethanol (7), so they would also be classified 
1-2

as Class I liquids. Thus, the current diesel fuel infrastructure could not be used to 

handle E-diesel unless the equipment was brought to NFPA Class I standards. 

Moreover, the flammability limits for ethanol are such that flammable mixtures can 

exist in tank ullage space. E-diesel blends containing 10% or more ethanol also have 

the same flammability limits as ethanol (2, 7). 

E-diesel operation also raises concerns related to potential adverse effects on engine and 

vehicle performance. E-diesel has a lower volumetric heat content (MJ/L), so some 

engine power loss will be experienced unless the fuel pump capacity can be increased. 

Other concerns relate to engine efficiency loss and overall performance due to the lower 

cetane number of E-diesel unless a cetane improver is included in the additive package. 

Increased fuel pump wear is a concern due to the decreased lubricity of ethanol. 

Alcohol fuels (methanol and, though to a lesser extent, ethanol) always increase 

materials compatibility concerns such as increased corrosion and elastomer 

incompatibility. Finally, due to the higher vapor pressure of ethanol, fuel pump vapor 

lock problems can increase. 

Although the above risks and concerns are potential issues, it bears noting that, in the 

several E-diesel fleet demonstrations performed to date, there have been no vehicular or 

fueling station incidents that have resulted in fires or explosions, nor has there been any 

mechanical failure of any fuel system part that can be directly attributed to the E-diesel 

fuel (3, 9). Nevertheless, the fact that these risks and concerns have been raised argues 

that a structured analysis of these issues be performed. 

In this study, TIAX performed a safety risk assessment and performance risk evaluation 

of E-diesel use in heavy-duty fleet vehicles as compared to standard diesel fuel use. The 

assessments were structured in the form of failure modes and effects analyses (FMEAs). 

In an FMEA, an evaluation team of experts in various aspects of the process under 

evaluation (in this case E-diesel and conventional fuel use in heavy-duty vehicles) 

brainstorms potential failures that may occur in the process, documents the cause(s) and 

effect(s) of the failure, and assigns ratings to the failure/effect corresponding to its likely 

probability, the severity or seriousness of the failure/effect, and whether appropriate 

controls are in place to detect and prevent the cause of the failure. The product of these 

three ratings in the analysis becomes a measure of the risk posed by the failure/effect. 

Following this initial assessment, failure modes ranking as high in risk are afforded 

additional consideration to identify recommended actions that could decrease the risk 

ranking, and the effects of these actions on the risk ranking are evaluated. 

The project was initiated with the collection of fuel property data relating to safety and 

performance issues that serve as the basis for completing the FMEA. An FMEA team 

was assembled and several FMEA meetings were held to brainstorm the potential failure 

modes with corresponding causes and effects, and to assign the three ratings noted 

above that give rise to the risk ranking. 
1-3

Results of this FMEA are presented in this report. Section 2 provides more detailed 

discussion of the FMEA methodology that was employed in the analyses. Section 3 

summarizes the outcomes of the safety risk FMEA and Section 4 summarizes the results 

of the parallel performance risk FMEA. Study conclusions are summarized in 

Section 5. 
2-1

2. FMEA Methodology 

An FMEA is a systematic and structured method of identifying product and process 

problems, assessing their significance, and identifying potential solutions that reduce 

their significance (10). The objective of an FMEA is to look for all the ways a product 

or process can fail (failure modes). Each failure mode has a cause and a potential effect. 

Some failure modes are more likely to occur than others, and each potential effect has a 

relative risk associated with it. The FMEA process is a way to identify the failure 

modes within a process or product and to identify actions to eliminate these. 

In an FMEA, the relative risk of a failure and its effect is determined by three factors: 

• Occurrence — the probability or frequency of the failure occurring 

• Severity — the seriousness of the effect of the failure mode 

• Detection — the probability of the failure being detected before the impact of the 

effect is realized 

Numerical rankings are assigned for each factor. The higher the ranking the greater is 

the potential harm posed by the failure and its effect. These rankings can be on any 

scale desired. Many organizations performing FMEAs use a scale of 1 to 10. Others 

use 1 to 5. Most FMEA practitioners believe that the minimum scale is 1 to 3. In this 

study, a 1 to 5 scale was chosen. Table 2-1 summarizes occurrence, severity, and 

detection descriptions associated with each numerical rating for the 1 to 5 scale chosen 

for this study. The overall measure of relative risk in an FMEA is termed the risk 

priority number (RPN). The RPN is the product of the three factors, occurrence • 

severity • detection. RPNs can then be used to rank the significance of the risk posed by 

the failure/effect and the need for corrective actions to reduce or eliminate the potential 

failure mode. 

FMEAs are teamed-based. Thus, in performing an FMEA, a team is assembled 

composed of individuals knowledgeable in various aspects of the process or product 

under evaluation. FMEA teams are usually comprised of four to six persons. The 

FMEA process consists of having the FMEA team meet and brainstorm potential failure 

modes of the process or product, identify the cause(s) of the failure, the effect(s) of the 

failure, and the current controls in place to detect the failure before the effect occurs. 

Having all the potential failure modes, with associated causes, effects, and current 

controls identified, the FMEA team then assigns occurrence, severity, and detection 

rankings to each combination, allowing the calculation of the RPN for each 

combination. This allows ranking of the failure/effects in order of most (highest RPN) 

to least (lowest RPN) significance or relative risk. The assignment of the occurrence, 

severity, and detection ratings is by team consensus. Consensus must be reached for the 

process to be effective. 
2-2

Table 2-1. Occurrence, Severity, and Detection Ratings

Occurrence 

Rating Description 

5 Very high. Almost certain to occur repeatedly. 

4 High. Very likely to occur. 

3 Moderate. Somewhat likely to occur occasionally. 

2 Low. Would occur under rare circumstances. 

1 Remote. Unlikely that failure would occur. 

 

Severity 

Rating Description 

5 Very high. Potential for great harm or death. Equipment destruction. 

4 High. Harm would require medical treatment. Substantial equipment damage. 

3 Moderate. Pain or discomfort. Some equipment or subsystem damage. 

2 Low. Some annoyance. No noticeable performance change. 

1 Negligible. End user would probably not notice 

 

Detection 

Rating Description 

5 Ineffective controls. Failure, effect, or hazard not detectable. 

4 Controls effective only sometimes. Failure or hazard detected only sometimes. 

3 Allows occasional occurrences of failure or hazardous condition. 

2 Allows rare occurrences of failure or hazardous condition. 

1 Almost certain the failure or hazardous condition will be detected. 

The end result of this first phase of the FMEA is a tabular summary that describes all 

failure modes identified, their causes and effects, the current controls in place, the 

occurrence (O) severity (S), and detection (D) ratings and the resulting RPN, ranked in 

order of highest to lowest RPN. This table generally has the form illustrated in 

Table 2-2. As suggested in the table, the occurrence rating can be associated with the 

cause of the failure (how likely will the cause occur), the severity rating with the effect 

of the failure (how damaging or injurious is the effect), and the detection rating with the 

current controls (how likely will the failure be detected so that action to prevent the 

failure can be taken). 
Table 2-2. FMEA Worksheet Template 

No. Item/Function Potential Failure Mode Causes of Failure O Effect(s) of Failure S Current Controls D RPN 

Process: Fleet use of E-Diesel Date:

FMEA Process 
2-4

The table also indicates another aspect of the FMEA process, that it generally consists of 

at least two phases. After the first phase, the ranked failure modes with current controls 

in place have been identified. In the second phase, the FMEA team identifies actions 

that can be taken to reduce the probability of the failure or reduce the magnitude of its 

effect, or additional controls that can be incorporated to increase the probability of 

detection. These actions are noted in the FMEA table, and their effects in reducing the 

impacts of the failure mode evaluated by assigning revised occurrence, severity, and 

detection ratings and calculating the resultant (reduced) RPN. This process can be 

repeated until the team concludes that an acceptable level of risk has been achieved, or 

that no further actions that can reduce risk are feasible. 

In preparation for a process FMEA of the type completed in this study, the FMEA team 

must review the process under evaluation. Toward this end, the team is supplied with as 

much information as can be assembled on the process. In performing an FMEA of a 

traditional industrial process, the team might expect to be able to review a process flow 

diagram with heat and material balance, a piping and instrumentation diagram (P&ID), 

and a tabulation of the properties of the materials involved in the process. 

The purpose of this study was to perform a safety and performance assessment of 

E-diesel use as an alternative diesel fuel. These assessments were structured as process 

FMEAs. To facilitate the evaluation, the E-diesel use process was defined as follows. 

The major safety risk posed by E-diesel is the increased risk of fire or explosion. 

Ethanol, based on its flash point, is an NFPA Class I liquid, the same class as gasoline. 

In contrast, diesel fuel is a Class II liquid. E-diesel blends containing 10% or more 

ethanol have the flash point of ethanol (7). Thus, the current diesel fuel infrastructure 

could not be used to handle E-diesel unless the equipment was brought to NFPA Class I 

standards. Moreover, E-diesel does not meet all the ASTM specifications for diesel 

fuel. Thus, it can not be sold as diesel at the retail level (7). This, coupled with the 

infrastructure incompatibility issues, means that any near term use will likely be 

confined to fleet operators with central fueling facilities. These can be either centrally 

fueled on-road or off-road vehicle fleets. Thus, the generalized process evaluated in the 

FMEAs performed in this study envisions the E-diesel being prepared by a fuel 

distributor by splash blending formulation components, then being transported to a fleet 

operator for fleet use. 

Many fuel distributors in the U.S. currently splash blend ethanol into gasoline by 

pouring the two components directly into tanker trucks for delivery to customers 

marketing gasoline E10. It is likely that E-diesel would be similarly prepared for fleet 

customers using this fuel. Nevertheless, it was decided to include onsite E-diesel 

storage in blended form at the distributor in case this ever should occur. Therefore, the 

E-diesel preparation, transportation, and fleet vehicle use process evaluated in the 

FMEA was as follows. The fuel distributor has dedicated a separate fixed roof storage 

tank at the distribution facility for servicing his fleet customers using E-diesel. He 

prepares the E-diesel blend as needed by taking delivery of tanker truck, rail car, or 

barge delivery of complete fuel grade ethanol shipments, then splash blending the 
2-5

ethanol, additive package, and onsite diesel fuel from other diesel storage tanks at the 

facility into the dedicated E-diesel tank. As fleet customers require fuel deliveries, he 

dispatches tanker trucks from his tanker fleet, filled from the dedicated E-diesel storage 

tank, to refill customer fueling facility underground storage tanks. The customer refuels 

his E-diesel fleet from his onsite storage into vehicles for use. The process flow 

diagram for this process is given in Figure 2-1. 

The FMEA team for this study was comprised of four individuals knowledgeable in 

alternative fuel formulation and alternative fueled vehicle use, alternative fuel 

properties, the risks associated with various alternative fuel use scenarios, and vehicle 

design and operation. Extensive experience in methanol-fueled heavy-duty vehicle 

design and demonstration, and methanol fueling station design and operation from the 

many development and demonstrations programs performed in the 1980s through early 

1990s was represented on the team. This methanol vehicle and fueling infrastructure 

experience proved of great benefit to the evaluations. 

No 2. 

diesel

Additives

Storage

Tank

Storage

Tank

Fuel

dispenser

Vehicle fuel

tank

Engine

Fuel pump

Fuel Distributor Fleet Operator

Fuel grade EtOH

Figure 2-1. E-Diesel Process Flow Diagram 
3-1

3. Safety Assessment 

As noted in Section 2, the major safety risk posed by E-diesel is the increased risk of 

fire or explosion. Thus, the properties of E-diesel of greatest importance to the safety 

FMEA are those associated with its combustion. Table 3-1 summarizes many of these 

properties for an E-diesel blend containing 15% ethanol (E-15). For comparison, the 

corresponding properties for a typical diesel fuel, ethanol, methanol, and gasoline are 

also noted. Of particular significance to the FMEA is the observation in the table that 

E-15 has the same Reid vapor pressure, flammability limits, and flash point (generally 

the lower flammability limit, or very near it) as ethanol (2, 7). It has the same 

autoignition temperature as diesel fuel because the diesel autoignition temperature is 

lower than that of ethanol. The properties of only one E-diesel blend are shown in 

Table 3-1. The E-diesel properties noted above, being the same as for ethanol, would be 

the same for all E-diesel blends containing 10% or more ethanol, although blends 

containing less than about 4% ethanol have vapor pressure and flammability 

characteristics closer to those of diesel fuel. The other properties noted in the table — 

density, heating values, and latent heat of vaporization — are calculated based on the 

fraction of ethanol in the blend and the assumption that there is no differential volume 

change when blending ethanol, additive, and diesel fuel (15 L of ethanol combined with 

5 L of additive and 80 L of diesel yields 100 L of blend) and that the additive has the 

same density, heating value, and latent heat as diesel. Thus, the volumetric heating 

Table 3-1. Properties of E-Diesel and Other Fuels (2, 7, 11, 12, 13, 14) 

Property Diesel E-15 Ethanol Methanol Gasoline 

Reid Vapor Pressure, kPa (psi) <3 (<0.4) 15 (2.2) 15 (2.2)a 32 (4.6) 62 (9.0) 

Lower Flammability Limit 

 Concentration, vol% 0.6 3.3 3.3 6.0 1.4 

 Temperature, oC (°F) 64 (145) 13 (55) 13 (55) 7.2 (45) -45 (-49) 

Upper Flammability Limit 

 Concentration, vol% 5.6 19 19 37 7.6 

 Temperature, oC (°F) 150 (300) 42 (108) 42 (108) 43 (109) -20 (-4) 

Flash Point, oC (°F) 64 (145) 13 (55) 13 (55) 11 (52) -43 (-45) 

Autoignition Temperature, oC (°F) 230 (445) 230 (445) 366 (691) 385 (725) 300 (570) 

Density, kg/L (lb/gal) 0.863 (7.20) 0.851 (7.10) 0.785 (6.55) 0.792 (6.61) 0.791 (6.6) 

Vapor Specific Gravity, (air =1) 5.5 1.6 1.6 1.1 3.5 

Lower Heating Value 

 Mass, MJ/kg (Btu/lb) 42.6 

(18,300) 

40.4 

(17,400) 

27.0 

(11,600) 

20.0 

(8,600) 

43.9 

(18,900) 

 Volume, MJ/L (Btu/gal) 36.7 

(132,000) 

34.4 

(123,000) 

21.2 

(76,000) 

15.8 

(56,800) 

32.7 

(117,000) 

Higher Heating Value 

 Mass, MJ/kg (Btu/lb) 46.5 

(20,000) 

44.2 

(19,000) 

29.8 

(12,800) 

22.8 

(9,800) 

46.7 

(20,100) 

 Volume, MJ/L (Btu/gal) 40.2 

(144,000) 

37.7 

(135,000) 

23.4 

(83,900) 

18.1 

(64,800) 

34.8 

(125,000) 

Latent Heat of Vaporization, kJ/kg (Btu/lb) 270 (120) 350 (150) 840 (360) 1,170 (500) 350 (150) 

Diffusivity, cm2/s (ft2/hr) 0.046 (0.18) 0.10 (0.39) 0.10 (0.39) 0.14 (0.54) 0.064 (0.25) 

a

 Ethanol has blending Reid vapor pressure in hydrocarbon fuels of 120 to 125 kPa (17 to 18 psi). 
3-2

value (MJ/L) of E-15 is the weighted average (15% ethanol, 85% diesel) of the 

volumetric heating values of ethanol and diesel. Mass heating values and latent heats 

factor in component densities. Densities, heating values, and latent heats of other 

E-diesel blends with different ethanol content can be similarly calculated. 

Of particular importance to the safety assessment are the flammability limits of E-15, 

which are the same as ethanol as noted above. Figure 3-1 shows the flammability limit 

temperature range (range of temperature over which a flammable vapor concentration 

will exist over the corresponding liquid) for each of the fuels with data in Table 3-1. 

The figure shows that at temperatures above -20°C gasoline in an enclosed vapor space 

above the liquid is too concentrated (rich) to be flammable, while diesel fuel at 

temperatures below 64°C is too dilute (lean) to be flammable. However, the alcohol 

fuels, including the E-diesel, are flammable at common ambient temperatures above 

13°C. This means that, at common ambient temperatures, the vapor in a storage tank or 

vehicle fuel tank containing E-diesel is flammable or explosive. 

All the failure modes defined in the safety FMEA are associated with the risk of fire or 

an explosion. Many are directly associated with explosions in the ullage of a storage or 

vehicle fuel tank. All these failure modes apply to one of the various elements of the 

fuel preparation and storage at the fuel distributor, fuel transportation to the fleet user, 

fuel storage and dispensing at the fleet fueling facility, and vehicle fuel use process 

shown in the process flow diagram in Figure 2-1. 

-50 -25 0 25 50 75 100 125 150

Temperature °C

Diesel

E-Diesel

Ethanol

Methanol

Gasoline

Figure 3-1. Flammability Limit Temperature Range for E-Diesel and Other Fuels 
3-3

3.1 Initial FMEA Risk Ranking 

Table 3-2 is the completed FMEA worksheet resulting from the initial FMEA 

identification of potential failure modes, and their causes and effects. Each failure mode 

combination is numbered and is associated with one of the process elements in the 

process flow diagram given in Figure 2-1. As noted previously, the main safety concern 

regarding E-diesel arises from the relatively higher flammability of E-diesel compared 

to diesel. Ignition of E-diesel fuel leading to an explosion or a pool fire at various 

points in the fuel chain between bulk storage at a terminal and vehicle operation became 

the focus of this FMEA. 

Following the definition of failure modes, it was decided that a safety risk FMEA be 

first performed for conventional diesel fuel and gasoline for the defined failure modes. 

This was deemed a necessary exercise by the FMEA team because it would create 

benchmarks for assigning relative risk to the E-diesel case. Tables 3-3 and 3-4 are the 

results of the baseline assessments for diesel and gasoline respectively. In both tables 

failure modes are ranked in order of decreasing RPN. As can be seen from Tables 3-3 

and 3-4, and not surprisingly, the failure modes for diesel in general have lower RPNs 

than for gasoline. This is a reflection of diesel being a lower combustion hazard. 

3.1.1 Gasoline and Diesel Ratings 

Risks associated with gasoline and diesel were analyzed throughout the fuel chain from 

bulk terminal to truck vehicle operation. The risks associated with the fuel itself related 

to vapors igniting in closed spaces and fuel igniting in open spaces. 

The risks of vapor ignitions were considered for vapor spaces in the bulk terminal, 

tanker truck, underground tank, and the on-board vehicle tank. Occurrence (O) ratings 

for explosion in tanks for diesel and gasoline typically were 1 or 2 indicating remote to 

low potential reflecting the fact that vapors in these tanks have little opportunity for 

forming combustible mixtures. The effect of failure and the resulting severity (S) 

ratings for the explosions are, however, always high and are reflected by the high and 

very-high potential for harm (ratings of 4 and 5). Current controls for either diesel or 

gasoline fuels in general do not allow the detection and arrest of an explosion. It is not 

expected to be different for E-diesel either. Consequently, ratings for detection (D) 

related to explosions were always awarded the highest value of 5 corresponding to nondetection. The RPN for explosion related failure modes ranged between 20 and 40 for 

diesel and gasoline. 

Diesel ullage spaces normally do not contain flammable vapors. The vapor pressure 

results in a mixture that is too lean to form a combustible mixture until the fuel is above 

64°C. Ambient temperatures on the hottest days are below 45°C, so vapors in bulk 

storage tanks are too lean to burn under normal circumstances. Diesel vehicle fuel tanks 

are exposed to higher temperature because hot fuel is recirculated from the engine to the 

fuel tank. On hot days, the fuel tank can be exposed to direct sunlight and heat radiation 
Table 3-2. Potential Safety Risk Failure Modes 

Process: Fleet use of E-Diesel D

FMEA Process 

No. Item/Function 

Potential Failure 

Mode Causes of Failure O Effect(s) of Failure S Current Controls D RPN 

1 Fuel distributor 

storage tank 

Explosion in tank Ignition source in vapor return line Explosion in piping Flame arresters, Class 1 

gasoline-rated tank 

2 Fuel distributor 

storage tank 

Explosion in tank Ignition source at tank vent Flame propagation through 

vent, explosion in tank and piping 

3 Tanker truck Explosion in tank 

with substantial ullage 

Ignition source in vapor return line while open 

Major equipment/vehicle damage and possible personal injury and death 

4 Tanker truck Spilled fuel fire Traffic accident, overturned tanker, 

fuel spill, ignition source ignites 

Pool fire, potential vehicle fire, personal injury or death 

 DOT placard 

5 Fleet operator 

storage tank 

Explosion in tank Ignition source in fill opening while 

open 

Blows out tank manhole and fill openings, resulting in possible injury 

 Wooden tank-dipstick 

6 Fleet operator 

storage tank 

Explosion in tank Ignition source in tank vent Flame propagates into tank 

and explosions pop covers causing personal injury 

7 Fuel transfer 

hose 

Spilled fuel fire Rupture/failure of transfer hose Pool fire (hose volume) 

8 Fuel dispenser Spilled fuel fire Inattention during vehicle refueling 

results in fuel nozzle falling from fill opening. Resulting fuel spill produces a flammable concentration that encounters an ignition source 

 Pool fire, potential vehicle fire 

9 Vehicle fuel 

tank 

Explosion in tank Ignition source in fill opening while 

open, looking into tank 

Flame projected from fill opening, personal injury 

10 Vehicle fuel 

tank 

Explosion in tank Static discharge ignition source in fill 

opening while open 

Flame projected from fill opening, personal injury 

11 Vehicle fuel 

tank vent 

Explosion in tank Ignition source outside tank vent 

(filler cap), filler cap fails to stop flame 

Flame projected from fill opening, personal injury 

 Filler cap 

12 Vehicle fuel 

tank vent 

Flame at opening Ignition source outside tank vent 

(filler cap) 

 Puff flame 

13 Vehicle fuel 

tank 

Spilled fuel fire Traffic accident, fuel spill, ignition 

source ignites 

Pool fire, potential vehicle fire, personal injury or death 

14 Vehicle fuel 

tank 

Fuel fire Fuel leak while parked, flammable 

mixture encounters ignition source, ignites 

Pool fire, potential vehicle fire, personal injury 

15 Vehicle fuel 

tank 

Explosion in tank Ignition source in tank, level detector 

fault 

 Fuel tank, vehicle damage 

16 Engine Engine fire Fuel line leak onto hot manifold with 

engine running 

Engine damage, potential vehicle fire, personal injury or death 

3-4
Table 3-3. Safety Risk FMEA Ratings for Diesel Fuel Use 

Process: Fleet use of Diesel D

FMEA Process 

No. Item/Function 

Potential Failure 

Mode Causes of Failure O Effect(s) of Failure S Current Controls D RPN 

4 Tanker truck Spilled fuel fire Traffic accident, overturned tanker, fuel 

spill, ignition source ignites 

3 Pool fire, potential vehicle fire, 

personal injury or death 

5 DOT placard 3 45 

13 Vehicle fuel 

tank 

Spilled fuel fire Traffic accident, fuel spill, ignition 

source ignites 

3 Pool fire, potential vehicle fire, 

personal injury or death 

5 3 45 

9 Vehicle fuel 

tank 

Explosion in tank Ignition source in fill opening while 

open, looking into tank 

2 Flame projected from fill 

opening, personal injury 

4 5 40 

10 Vehicle fuel 

tank 

Explosion in tank Static discharge ignition source in fill 

opening while open 

2 Flame projected from fill 

opening, personal injury 

4 5 40 

15 Vehicle fuel 

tank 

Explosion in tank Ignition source in tank, level detector 

fault 

2 Fuel tank, vehicle damage 4 5 40 

16 Engine Engine fire Fuel line leak onto hot manifold with 

engine running 

4 Engine damage, potential 

vehicle fire, personal injury or death 

5 2 40 

2 Fuel distributor 

bulk storage tank 

Explosion in tank Ignition source at tank vent 1 Flame propagation through 

vent, explosion in tank and piping 

5 5 25 

3 Tanker truck Explosion in tank 

with substantial ullage 

Ignition source in vapor return line while open 

1 Major equipment/vehicle 

damage and possible personal injury and death 

5 5 25 

7 Fuel transfer 

hose 

Spilled fuel fire Rupture/failure of transfer hose 2 Pool fire (hose volume) 4 3 24 

6 Fleet operator 

storage tank 

Explosion in tank Ignition source in tank vent 1 Flame propagates into tank 

and explosions pop covers causing personal injury 

4 5 20 

11 Vehicle fuel 

tank vent 

Explosion in tank Ignition source outside tank vent (filler 

cap), filler cap fails to stop flame 

1 Flame projected from fill 

opening, personal injury 

4 Filler cap 5 20 

5 Fleet operator 

storage tank 

Explosion in tank Ignition source in fill opening while 

open 

1 Blows out tank manhole and 

fill openings, resulting in possible injury 

4 Wooden tank-dipstick 5 20 

8 Fuel dispenser Spilled fuel fire Inattention during vehicle refueling 

results in fuel nozzle falling from fill opening. Resulting fuel spill encounters ignition source 

2 Pool fire, potential vehicle fire 4 2 16 

14 Vehicle fuel 

tank 

Fuel fire Fuel leak while parked, flammable 

mixture encounters ignition source, ignites 

2 Pool fire, potential vehicle fire, 

personal injury 

4 2 16 

12 Vehicle fuel 

tank vent 

Flame at opening Ignition source outside tank vent (filler 

cap) 

1 Puff flame 2 5 10 

1 Fuel distributor 

storage tank 

Explosion in tank Ignition in vapor return line 0 Explosion in piping 5 Flame arresters, Class 

1 gasoline-rated tank 

5 0 
Table 3-4. Safety Risk FMEA Ratings for Gasoline Use 

Process: Fleet use of Gasoline 

FMEA Process 

No. Item/Function 

Potential Failure 

Mode Causes of Failure 

O Effect(s) of Failure S Current Controls 

D RPN 

4 Tanker truck Spilled fuel fire Traffic accident, overturned tanker, 

fuel spill, ignition source ignites 

4 Pool fire, potential vehicle fire, 

personal injury or death 

5 DOT placard 3 60 

13 Vehicle fuel 

tank 

Spilled fuel fire Traffic accident, fuel spill, ignition 

source ignites 

4 Pool fire, potential vehicle fire, 

personal injury or death 

5 3 60 

9 Vehicle fuel 

tank 

Explosion in tank Ignition source in fill opening while 

open, looking into tank 

2 Flame projected from fill 

opening, personal injury 

4 5 40 

10 Vehicle fuel 

tank 

Explosion in tank Static discharge ignition source in fill 

opening while open 

2 Flame projected from fill 

opening, personal injury 

4 5 40 

6 Fleet operator 

storage tank 

Explosion in tank Ignition source in tank vent 2 Flame propagates into tank 

and explosions pop covers causing personal injury 

4 5 40 

11 Vehicle fuel 

tank vent 

Explosion in tank Ignition source outside tank vent (filler 

cap), filler cap fails to stop flame 

2 Flame projected from fill 

opening, personal injury 

4 Filler cap 5 40 

15 Vehicle fuel 

tank 

Explosion in tank Ignition source in tank, level detector 

fault 

2 Fuel tank, vehicle damage 4 5 40 

16 Engine Engine fire Fuel line leak onto hot manifold with 

engine running 

4 Engine damage, potential 

vehicle fire, personal injury or death 

5 2 40 

7 Fuel transfer 

hose 

Spilled fuel fire Rupture/failure of transfer hose 3 Pool fire (hose volume) 4 3 36 

12 Vehicle fuel 

tank vent 

Flame at opening Ignition source outside tank vent (filler 

cap) 

3 Puff flame 2 5 30 

2 Fuel distributor 

bulk storage tank 

Explosion in tank Ignition source at tank vent 1 Flame propagation through 

vent, explosion in tank and piping 

5 5 25 

1 Fuel distributor 

storage tank 

Explosion in tank Ignition in vapor return line 1 Explosion in piping 5 Flame arresters, Class 1 

gasoline-rated tank 

5 25 

3 Tanker truck Explosion in tank 

with substantial ullage 

Ignition source in vapor return line while open 

1 Major equipment/vehicle 

damage and possible personal injury and death 

5 5 25 

8 Fuel dispenser Spilled fuel fire Inattention during vehicle refueling 

results in fuel nozzle falling from fill opening. Resulting fuel spill encounters ignition source 

3 Pool fire, potential vehicle fire 4 2 24 

14 Vehicle fuel 

tank 

Fuel fire Fuel leak while parked, flammable 

mixture encounters ignition source, ignites 

3 Pool fire, potential vehicle fire, 

personal injury 

4 2 24 

5 Fleet operator 

storage tank 

Explosion in tank Ignition source in fill opening while 

open 

1 Blows out tank manhole and 

fill openings, resulting in possible injury 

4 Wooden tank-dipstick 5 20 

3-6
3-7

from asphalt resulting in fuel temperatures higher than ambient temperatures, giving rise 

to flammable fuel vapors. 

Fuel tanks are typically not exposed to ignition sources, however. Fleet fueling facilities 

are subject to safety precautions that prevent smoking, idling vehicles, welding, 

electrical arcs, and other ignition sources. Ignition sources are normally not present near 

the vehicle fuel tank. Fleet diesel trucks and buses typically do not have in-tank fuel 

pumps. Possible ignition sources include human error, sparks, or fires from vehicle 

collisions, or possibly the fuel tank level sensor. Again, the vapor space in fuel tanks is 

typically not combustible, limiting the opportunity for in-tank vapor ignition. Because 

of the greater potential to heat up fuel during vehicle operation, scenarios involving 

explosions in diesel vehicle tanks received an occurrence rating of 2 compared to 

occurrence ratings of 1 for diesel fuel infrastructure tanks. 

Similarly, gasoline ullage spaces normally do not contain flammable vapors. The vapor 

pressure results in a mixture that is too rich to form a combustible mixture until the fuel 

drops below -20°C. Flammable vapors can form under very cold ambient conditions or 

circumstances where fresh air is introduced into a fuel tank. 

Spilled gasoline and diesel from fuel handling, leaks, or traffic accidents result in the 

risk of fires with the potential for human injury and extensive vehicle damage. Fuel 

spills can occur during bulk fuel transfers and vehicle refueling. Such spills occur in 

controlled environments where safety procedures are intended to eliminate ignition 

sources. Occurrence ratings for fires resulting in damage or injury from spilled fuel for 

diesel were 2 or 3. These ratings reflect the potential likelihood of incidental fuel spills 

combined with the potential for igniting diesel fuel. For the same scenarios, gasoline 

spills received ratings of 3 or 4, which reflect the fuel’s higher vapor pressure and the 

potential to form a flammable vapor cloud that could reach an ignition source. 

Engine fires resulting from fuel leaks received occurrence ratings of 4 for both gasoline 

and diesel. Exhaust manifolds and electrical equipment provide heat for fuel 

vaporization and a source of ignition. 

Similar to vapor explosions, the effect of failure and the resulting severity ratings for 

fuel fires are, however, always high and are reflected by the high and very-high 

potential for harm (ratings of 4 and 5). Ratings for detection related to fires were rated a 

2 or 3 because the vehicle driver or personnel associated with an accident have the 

opportunity to escape injury and possibly make use of a fire extinguisher. 

The RPN for fuel spill related failure modes ranged between 16 and 45 for diesel and 

between 24 and 60 for gasoline. The highest RPN ratings were 45 for fires arising from 

diesel spills caused by traffic accidents (either with diesel tanker trucks or vehicles) and 

60 for similar incidents with gasoline fuel trucks or vehicles. 
3-8

3.1.2 E-Diesel FMEA Rating 

Table 3-5 presents the results of the initial FMEA rating of the same safety risk failure 

modes for E-diesel use, again with failure modes ranked in order of decreasing RPN. 

Some safety related failure modes for E-diesel represented greater risk potential than 

those for diesel. These failure modes can be grouped into situations involving 

flammable vapors in closed spaces and fuel leaks or spills in open areas. 

Fuel vapors in E-diesel tanks and piping typically form a flammable concentration. The 

presence of a flammable mixture resulted in occurrence ratings of 2 to 4 for the 

scenarios involving explosions in tanks or piping compared with diesel ratings of 1 to 2. 

The occurrence rating corresponded to the FMEA team’s assessment of the likelihood of 

an ignition source being present combined with the flammable vapor concentrations that 

occur with E-diesel. 

The highest occurrence risk appears to be in the vehicle fuel tank. Limited anecdotal 

experience indicates that ignition leading to an explosion can occur in diesel tanks 

(perhaps when the truck operator is inspecting the fuel level). Many diesel tanks have 

very large fill openings (about 3-inch diameter). The large fill opening may provide 

access for tank maintenance but also provides the careless operator with an opportunity 

to view the fuel level (perhaps when the level gauge does not appear to work). As a 

result of this potentially dangerous (and not uncommon) behavior, the occurrence rating 

for this failure mode for E-diesel (No. 9 in Table 3-5) was raised from 2 to 4 and as a 

result the RPN increased to 80 compared with 40 for diesel and gasoline. This failure 

mode resulted in the highest RPN for the E-diesel safety FMEA. 

Ignition sources other than operator carelessness could also result in an explosion in the 

vehicle tank. The most likely source of ignition could be a static discharge during 

fueling when the tank is open. The occurrence rating for a static discharge was 

estimated to be lower than for operator intervention because there would be 

opportunities to discharge any potential static charges prior to opening the filler cap. 

Flammable E-diesel vapors could pose a significant risk in bulk storage facilities. 

Igniting a vapor mixture in a bulk fuel facility could result in a piping explosion and 

possibly affect other fuel storage equipment. Potential ignition sources could reach the 

piping through a vent or vapor return line from the truck loading rack. Underground 

E-diesel storage tanks at the fleet operator’s site will contain vapor air mixtures that 

would be flammable under many ambient temperature conditions. The vapor space 

would be too lean to burn only when the fuel temperature drops below 13°C. Ignition 

sources could enter the underground tank either through the vent or the tank opening 

during filling. E-diesel delivery trucks would operate while containing a flammable 

vapor mixture that increases in quantity after each fuel delivery. The truck would be 

sealed while driving on the road and fire safety precautions would be enforced during 

fuel drops. 
Table 3-5. Initial Safety Risk FMEA Ratings for E-Diesel Use 

Process: Fleet use of E-Diesel D

FMEA Process 

No. Item/Function 

Potential Failure 

Mode Causes of Failure 

O Effect(s) of Failure S Current Controls 

D RPN 

9 Vehicle fuel 

tank 

Explosion in tank Ignition source in fill opening while 

open, looking into tank 

4 Flame projected from fill 

opening, personal injury 

4 5 80 

10 Vehicle fuel 

tank 

Explosion in tank Static discharge ignition source in fill 

opening while open 

3 Flame projected from fill 

opening, personal injury 

4 5 60 

4 Tanker truck Spilled fuel fire Traffic accident, overturned tanker, 

fuel spill, ignition source ignites 

4 Pool fire, potential vehicle fire, 

personal injury or death 

5 DOT placard 3 60 

6 Fleet operator 

storage tank 

Explosion in tank Ignition source in tank vent 3 Flame propagates into tank 

and explosions pop covers causing personal injury 

4 5 60 

11 Vehicle fuel 

tank vent 

Explosion in tank Ignition source outside tank vent 

(filler cap), filler cap fails to stop flame 

3 Flame projected from fill 

opening, personal injury 

4 Filler cap 5 60 

13 Vehicle fuel 

tank 

Spilled fuel fire Traffic accident, fuel spill, ignition 

source ignites 

4 Pool fire, potential vehicle fire, 

personal injury or death 

5 3 60 

2 Fuel distributor 

bulk storage tank 

Explosion in tank Ignition source at tank vent 2 Flame propagation through 

vent, explosion in tank and piping 

5 5 50 

1 Fuel distributor 

storage tank 

Explosion in tank Ignition in vapor return line 2 Explosion in piping 5 Flame arresters, Class 1 

gasoline-rated tank 

5 50 

5 Fleet operator 

storage tank 

Explosion in tank Ignition source in fill opening while 

open 

2 Blows out tank manhole and 

fill openings, resulting in possible injury 

4 Wooden tank-dipstick 5 40 

15 Vehicle fuel 

tank 

Explosion in tank Ignition source in tank, level detector 

fault 

2 Fuel tank, vehicle damage 4 5 40 

16 Engine Engine fire Fuel line leak onto hot manifold with 

engine running 

4 Engine damage, potential 

vehicle fire, personal injury or death 

5 2 40 

12 Vehicle fuel 

tank vent 

Flame at opening Ignition source outside tank vent 

(filler cap) 

3 Puff flame 2 5 30 

3 Tanker truck Explosion in tank 

with substantial ullage 

Ignition source in vapor return line while open 

1 Major equipment/vehicle 

damage and possible personal injury and death 

5 5 25 

7 Fuel transfer 

hose 

Spilled fuel fire Rupture/failure of transfer hose 2 Pool fire (hose volume) 4 3 24 

8 Fuel dispenser Spilled fuel fire Inattention during vehicle refueling 

results in fuel nozzle falling from fill opening. Resulting fuel spill encounters ignition source 

3 Pool fire, potential vehicle fire 4 2 24 

14 Vehicle fuel 

tank 

Fuel fire Fuel leak while parked, flammable 

mixture encounters ignition source, ignites 

3 Pool fire, potential vehicle fire, 

personal injury 

4 2 24 
3-10

The greatest risk for ignition leading to an explosion would occur during fuel transfers. 

Because trained personnel who follow safety precautions are responsible for fuel 

transfers, adding safety measures for fuel delivery trucks would be a lower priority than 

other steps in the fuel chain. Scenarios involving explosions in the tank caused by a 

static discharge or ignition source other than operator negligence receive occurrence 

ratings of 3 and total RPN ratings ranging from 40 to 60 for E-diesel. Overall, 

explosion related RPNs for E-diesel ranged from 40 to 80, a range twice that for diesel 

fuel or gasoline use. 

Spilled fuel fires resulting from accidents involving tanker trucks or fleet vehicles 

resulted in the highest RPN for both gasoline and diesel (60 and 45 respectively). For 

E-diesel use, accident related failure modes were deemed to have the same levels of 

occurrence and severity as those for gasoline use, with the same RPN of 60. However, 

the potential for flammable vapors forming with E-diesel spills may be less than that for 

a gasoline spill. The higher vapor pressure of gasoline combined with a lower lean 

flammability limit could produce a larger flammable vapor cloud than that formed with 

the ethanol component of E-diesel vapor. Furthermore, since ethanol represents only 10 

to 15 percent of E-diesel, a fuel spill will result in a weathering effect with a smaller 

vapor cloud forming over time than a pure ethanol spill. 

The rating system did not allow for a differentiation between the risks of gasoline and 

E diesel spills as they both produce flammable vapor clouds. The scenarios involving 

spilled fuel involved a vehicle accident or failed fuel line. Both vehicle and tanker truck 

accidents resulted in RPN scores of 60. Failed fuel lines resulted in lower RPN scores 

because of the greater opportunity for the vehicle operator to safely evacuate the scene 

of an accident. 

Finally, fuel fires related to leaky fuel lines, hose ruptures, and human errors resulted in 

relatively lower RPNs for all three fuels as can be seen in Tables 3-3, 3-4 and 3-5. The 

engine fire scenarios resulted in the same RPN of 40 for diesel, gasoline, and E-diesel 

because of the presence of hot manifolds to vaporize the fuel and provide ignition 

sources in the engine compartment. Electrical components also provide ignition 

sources. Several safety assessments comparing methanol with gasoline and diesel 

attempted to derive a relative safety ranking for fuel leaks in the engine compartment 

based on fuel properties (12). In practice engine compartment fires have occurred with 

both identical diesel and methanol buses. The motion of air, hot surfaces, and ignition 

sources provide many opportunities for fuel leaks to ignite, and flammable 

concentrations of all three fuels will exist in the engine compartment following a fuel 

release onto a hot engine. 

Spilled fuel from fuel dispensers received a relatively low RPN rating of 24 for E-diesel 

(and gasoline) which was higher than the RPN of 16 for diesel. The small quantity of 

fuel spilled combined with the vehicle operator’s potential ability to react to the fire 

makes this risk smaller than those associated with larger fuel spills. 
3-11

3.2 Post-Action Revised FMEA Safety Risk Ranking 

As discussed in Section 2, an important element of the FMEA process after ranking the 

relative risk of failure modes identified is to recommend actions or process 

modifications for high ranked failure modes that will reduce the probability of the 

failure, mitigate its effects, or improve the process controls to enhance failure detection. 

In this evaluation, only recommended actions that would reduce the frequency of 

occurrence were identified for high-ranking failure modes. The FMEA team agreed that 

only these actions made sense, and the severity of the effects could not be reduced nor 

could the probability of detection be fruitfully increased. The team defined 

recommended actions for failure modes in order of decreasing RPN beginning with the 

highest ranked failure mode, until an RPN that was the lower of gasoline or diesel RPN 

for the same failure mode was reached, and was ostensibly a tolerable risk. 

Table 3-6 presents the results from the recommended actions. A common action 

recommended for storage tank vents and vehicle fuel tank fill ports, is the installation of 

flame arresters. As can be seen in Table 3-6, the failure mode with the highest initial 

RPN is the explosion in a vehicle fuel tank. Current diesel vehicle fuel tank fill ports are 

simply capped. Several measures could be used to prevent an ignition source reaching 

the tank vapors. A simple flapper valve, similar to the type on gasoline fueled cars, 

would eliminate the opportunity for most vehicle operators to inspect the tank contents. 

The fuel tank could also be modified to accommodate a flame arrester in the filler neck 

and tank vent. The flame arrester would also prevent a flame from propagating into the 

tank vapors. A recent NREL study (15) showed that flame arresters for tanks with fill 

necks can be of fairly simple design while being quite effective in preventing tank 

explosions when an ignition source is intentionally placed into the fill opening. The 

same study recommended that vehicle E-diesel fuel tanks be equipped with blow out 

panels to prevent tank and vehicle damage if an explosion does occur. However, the 

FMEA team felt this was not necessary and has the disadvantage of guaranteeing a 

spilled fuel fire in situations in which the fuel tank did not rupture. 

Another approach would be to install a dry break fuel fitting. The dry break fitting closes 

when the tank is not being filled. Both a fill and vapor return fitting could be used to 

collect displaced fuel vapors. Many ethanol and methanol vehicles have been equipped 

with either dry break fueling fittings or flame arresters. Dry break fittings have also been 

used with vapor recovery to meet air quality constraints in California. An alternative 

design to the conventional diesel fill opening is thus highly recommended. 

A fuel vapor space could also ignite if an ignition source were present at the tank vent. 

Thus, a flame arrester in the tank vent is also recommended to reduce the risk of igniting 

the tank vapor space. As indicated in Table 3-6, a flame arrester is expected to reduce 

the vehicle fuel tank explosion risk occurrence rating to low (2) from high (4) and the 

resulting RPN can be reduced to 40 from 80. As noted in Table 3-6, other explosion 

failure mode occurrences were also mitigated through the recommended installation of 
Table 3-6. Revised Safety Risk FMEA Ratings for E-Diesel Use 

Process: Fleet use of E-Diesel Da

FMEA Process 

No. Item/Function 

Potential Failure 

Mode Causes of Failure 

O Effect(s) of Failure S Current Controls 

D RPN 

9 Vehicle fuel 

tank 

Explosion in tank Ignition source in fill opening while 

open, looking into tank 

4 Flame projected from fill opening, 

personal injury 

4 5 80 Fla

lea

10 Vehicle fuel 

tank 

Explosion in tank Static discharge ignition source in fill 

opening while open 

3 Flame projected from fill opening, 

personal injury 

4 5 60 Gr

4 Tanker truck Spilled fuel fire Traffic accident, overturned tanker, 

fuel spill, ignition source ignites 

4 Pool fire, potential vehicle fire, 

personal injury or death 

5 DOT placard 3 60 

6 Fleet operator 

storage tank 

Explosion in tank Ignition source in tank vent 3 Flame propagates into tank and 

explosions pop covers causing personal injury 

4 5 60 Fla

11 Vehicle fuel 

tank vent 

Explosion in tank Ignition source outside tank vent 

(filler cap), filler cap fails to stop flame 

3 Flame projected from fill opening, 

personal injury 

4 Filler cap 5 60 Fla

13 Vehicle fuel 

tank 

Spilled fuel fire Traffic accident, fuel spill, ignition 

source ignites 

4 Pool fire, potential vehicle fire, 

personal injury or death 

5 3 60 

2 Fuel distributor 

bulk storage tank 

Explosion in tank Ignition source at tank vent 2 Flame propagation through vent, 

explosion in tank and piping 

5 5 50 Fla

1 Fuel distributor 

storage tank 

Explosion in tank Ignition in vapor return line 2 Explosion in piping 5 Flame arresters, 

Class 1 gasolinerated tank 

5 50 Fla

5 Fleet operator 

storage tank 

Explosion in tank Ignition source in fill opening while 

open 

2 Blows out tank manhole and fill 

openings, resulting in possible injury 

4 Wooden tankdipstick 5 40 

15 Vehicle fuel 

tank 

Explosion in tank Ignition source in tank, level detector 

fault 

2 Fuel tank, vehicle damage 4 5 40 Int

de

16 Engine Engine fire Fuel line leak onto hot manifold with 

engine running 

4 Engine damage, potential vehicle 

fire, personal injury or death 

5 2 40 

12 Vehicle fuel 

tank vent 

Flame at opening Ignition source outside tank vent 

(filler cap) 

3 Puff flame 2 5 30 

3 Tanker truck Explosion in tank 

with substantial ullage 

Ignition source in vapor return line while open 

1 Major equipment/vehicle damage 

and possible personal injury and death 

5 5 25 

7 Fuel transfer 

hose 

Spilled fuel fire Rupture/failure of transfer hose 2 Pool fire (hose volume) 4 3 24 

8 Fuel dispenser Spilled fuel fire Inattention during vehicle refueling 

results in fuel nozzle falling from fill opening. Resulting fuel spill encounters ignition source 

3 Pool fire, potential vehicle fire 4 2 24 

14 Vehicle fuel 

tank 

Fuel fire Fuel leak while parked, flammable 

mixture encounters ignition source, ignites 

3 Pool fire, potential vehicle fire, 

personal injury 

4 2 24 

3-12
3-13

flame arresters. Flame arresters are commonly used in the petroleum industry 

throughout the fuel chain and can be quite effective in ethanol and E-diesel uses as well, 

as noted above. 

The second highest RPN for the vehicle fuel tank failure mode involves ignition due to 

static electric discharge. Following the methanol fueling station design experience, a 

grounding wire is suggested to reduce the occurrence of this mode from a moderate (3) 

to a remote (1) possibility, consequently lowering the RPN from 60 to 20. The 

grounding wire would be attached to the vehicle being refueled prior to refueling to 

ground the vehicle to the fuel dispenser. 

Vehicle fuel tank explosions can also be caused by an ignition source in the tank itself. 

Diesel vehicles typically do not have in-tank fuel pumps that could serve as an ignition 

source, as noted above. However, a faulty fuel level detector could become an ignition 

source. Use of an intrinsically safe design would reduce the occurrence rating for this 

potential failure mode from low (2) to remote (1). 

Spilled fuel fires as a result of a major accident with an E-diesel tanker truck or 

destruction of an E-diesel vehicle fuel tank can result in a catastrophic situation. The 

RPN for these failure modes (Nos. 4 and 12 in Table 3-6) were 60 each. The FMEA 

team felt that unless extreme measures are taken, that are not common industry practices 

and economically unattractive, these failure modes could not be further mitigated. Some 

of these measures include special tanks with bladders and foam fillings that have been 

considered for alcohol-fueled vehicles, and are used in racing cars. However, on-road 

vehicle operators have not used these safety measures which add cost to the vehicle and 

pose reliability issues. Yet another mitigation measure is the installation of an automatic 

fire suppression system (AFSS). AFSSs are provided on various types of vehicles and 

heavy equipment. Many methanol transit and school buses were equipped with AFSSs 

to address concerns that methanol burns with an invisible flame and the fuel is more 

volatile than diesel. While many methanol vehicle fires would result in visible smoke 

from other combustible sources, some bus fleet operators found the AFSS to provide an 

added measure of safety. 

E-diesel would not result in an invisible flame; however, the fuel does have a higher 

vapor pressure than diesel, which may motivate vehicle operators to consider an AFSS. 

The higher vapor pressure may not present a substantially greater risk of fire for leak 

scenarios in the engine compartment where the exhaust manifold could ignite diesel as 

well as E-diesel. However, the higher vapor pressure fuel could result in a combustible 

fuel mixture under some fuel spill scenarios. 
3-14

Finally, the revised RPNs are ranked and presented in Table 3-7 after the recommended 

actions have been taken. The revised RPNs are further compared with gasoline and diesel 

RPNs. As noted in Table 3-7, by taking the recommended actions, RPN for E-diesel that 

were between 80 and 40 could be reduced to 40 to 20 in many cases. The revised RPN for 

each failure mode is now less than or equal to the lower of either diesel or gasoline failure 

mode correspondingly. While E-diesel presents some adverse safety risks, these can be 

mitigated through the recommended actions. However, the economic impact of mitigating 

these risks may not be practical in some cases. 
Table 3-7. Final Ranked Safety Risk FMEA Ratings for E-Diesel Use 

Process: Fleet use of E-Diesel D

FMEA Process 

No. Item/Function 

Potential Failure 

Mode Causes of Failure 

O Effect(s) of Failure S Current Controls 

D RPN 

4 Tanker truck Spilled fuel fire Traffic accident, overturned 

tanker, fuel spill, ignition source ignites 

4 Pool fire, potential vehicle fire, 

personal injury or death 

5 DOT placard 3 60 

13 Vehicle fuel 

tank 

Spilled fuel fire Traffic accident, fuel spill, ignition 

source ignites 

4 Pool fire, potential vehicle fire, 

personal injury or death 

5 3 60 

9 Vehicle fuel 

tank 

Explosion in tank Ignition source in fill opening while 

open, looking into tank 

4 Flame projected from fill 

opening, personal injury 

4 5 80 F

le

5 Fleet operator 

storage tank 

Explosion in tank Ignition source in fill opening while 

open 

2 Blows out tank manhole and 

fill openings, resulting in possible injury 

4 Wooden tank-dipstick 5 40 

16 Engine Engine fire Fuel line leak onto hot manifold 

with engine running 

4 Engine damage, potential 

vehicle fire, personal injury or death 

5 2 40 

12 Vehicle fuel 

tank vent 

Flame at opening Ignition source outside tank vent 

(filler cap) 

3 Puff flame 2 5 30 

2 Fuel distributor 

bulk storage tank 

Explosion in tank Ignition source at tank vent 2 Flame propagation through 

vent, explosion in tank and piping 

5 5 50 F

1 Fuel distributor 

storage tank 

Explosion in tank Ignition in vapor return line 2 Explosion in piping 5 Flame arresters, Class 1 

gasoline-rated tank 

5 50 F

3 Tanker truck Explosion in tank 

with substantial ullage 

Ignition source in vapor return line while open 

1 Major equipment/vehicle 

damage and possible personal injury and death 

5 5 25 

7 Fuel transfer 

hose 

Spilled fuel fire Rupture/failure of transfer hose 2 Pool fire (hose volume) 4 3 24 

8 Fuel dispenser Spilled fuel fire Inattention during vehicle refueling 

results in fuel nozzle falling from fill opening. Resulting fuel spill encounters ignition source 

3 Pool fire, potential vehicle fire 4 2 24 

14 Vehicle fuel 

tank 

Fuel fire Fuel leak while parked, flammable 

mixture encounters ignition source, ignites 

3 Pool fire, potential vehicle fire, 

personal injury 

4 2 24 

10 Vehicle fuel 

tank 

Explosion in tank Static discharge ignition source in 

fill opening while open 

3 Flame projected from fill 

opening, personal injury 

4 5 60 G

6 Fleet operator 

storage tank 

Explosion in tank Ignition source in tank vent 3 Flame propagates into tank 

and explosions pop covers causing personal injury 

4 5 60 F

11 Vehicle fuel 

tank vent 

Explosion in tank Ignition source outside tank vent 

(filler cap), filler cap fails to stop flame 

3 Flame projected from fill 

opening, personal injury 

4 Filler cap 5 60 F

15 Vehicle fuel 

tank 

Explosion in tank Ignition source in tank, level 

detector fault 

2 Fuel tank, vehicle damage 4 5 40 I

d
4-1

4. Performance Assessment 

As noted in Section 1, several concerns have been raised regarding potential adverse 

effects the use of E-diesel may have on engine performance and durability. Ethanol has 

fuel properties that are different than those of diesel fuel, and does not meet the ASTM 

D975 specification for diesel fuel. Thus, E-diesel blends may also fail to meet diesel 

fuel specifications if the additive package does not take this into consideration. 

Potential associated adverse engine effects could result. 

Table 4-1 summarizes the specifications for No. 2 diesel fuel, and notes the property 

values for a typical diesel fuel, for ethanol, and two E-diesel blends, E-10 and E-15. For 

comparison, properties for methanol, an alternative fuel that was subjected to several 

demonstration tests in diesel vehicles during the 1980s through early 1990s, are also 

noted. The data in Table 4-1 show that ethanol has a much lower cetane number than 

the diesel fuel specification, so one might expect E-diesel blends to also not meet the 

specification. However, data on two E-diesel blends show that these blends do meet the 

specification, most likely because the additive supplier for the blends took the need for a 

cetane improver into consideration and included a appropriate component into the 

additive mix. The same could be said for lubricity, as this property for the two blends 

with data in Table 4-1 not only met the diesel specification, but were comparable to, to 

superior to typical diesel fuels. The viscosity for the two blends in Table 4-1, while 

slightly lower than that for a typical diesel, also met the specification. The corrosivity 

as measured by copper strip corrosion method for the two blends was the same as 

typical diesel, and also within specification. E-diesel pour points were at lower 

temperature than for typical diesel, and cold filter plugging point was equivalent. 

Table 4-1. Properties Affecting Engine Performance of Several Fuels and Fuel 

Components (2, 3, 7, 14, 17, 18) 

Property 

No. 2 Diesel 

Specification, 

On-Road (16)

Typical 

Diesel E-10 E-15 Ethanol Methanol

Cetane number 40 min 45 to 50 52 45 5 to 15 0 to 4 

Lubricity 

SBOCLEa, g 4,300 4,050 5,000 

HFRRb, mm 0.54 0.52 0.50 0.48 0.28 

Viscosity, mm2/s @ 40°C 1.9 to 4.1 2.5 typ 2.2 2.25 1.1 0.58 

Sulfur, % 0.05 max 0.035 typ <0.035 <0.035 Neg Neg 

Copper corrosion No. 3 max 1A 1A 1A 1A 

Cloud point, °C (°F) -19 (-2) 13 to 27 

(55 to 81) 

-5, 17 

(23, 63) 

 

Pour point, °C (°F) -29 (-20) -32 to -54

(-25 to -65)

-46 to -54 

(-51 to -65) 

 

Cold filter plugging point, °C (°F) -19 (-2) -19 (-2) 

a

 Scuffling load ball-on-cylinder lubricity evaluator. b

 High frequency reciprocating rig. 
4-2

The cloud points for the E-diesel blends were significantly higher than for typical diesel. 

For diesel fuel, the cloud point is the temperature associated with the formation of wax 

crystals in the fuel. When the fuel temperature falls below this temperature, problems 

with fuel filter and other fuel system component clogging can arise. The much higher 

cloud point for some E-diesel blends in Table 4-1 suggests such problems might arise at 

typical ambient temperatures. However, clouding in E-diesel blends is thought to be 

caused by the growth of micelles in E-diesel micro-emulsions to visible micron size 

range (7). If this were the clouding mechanism instead of the formation of wax crystals, 

then filter and fuel system clogging problems would not be experienced. The higher 

cloud point temperatures in Table 4-1 were for blends prepared with emulsifiers (7). 

The low E-15 cloud point temperature (-5°C) in the table was prepared with an additive 

the supplier claims is a cosolvent. If the blend were indeed a solution, the micelle 

growth to become cloudy would not be a mechanism, and lower cloud point, more in 

keeping with that of diesel fuel would be expected. In any event, for cold flow 

purposes, cloud point may not be a useful test for E-diesel; cold filter plugging point 

would be more so. 

4.1 Initial FMEA Performance Impact Ranking 

Table 4-2 is the completed FMEA worksheet resulting from the initial FMEA 

identification of potential failure modes, and their causes and effects. Each failure mode 

combination is numbered and is associated with one on the process elements in the 

process flow diagram given in Figure 2-1. Many of the concerns noted in Section 1 that 

could lead to potential adverse engine performance and durability are captured in the 

failure modes noted in the table. 

The performance risk FMEA proceeded in a manner similar to the approach used for the 

safety risk FMEA discussed in Section 3. Thus, for the performance risk evaluation, 

occurrence, severity, and detection ratings were assigned for the failure mode, cause, 

effect, and current controls combinations associated with diesel fuel use first to serve as 

a baseline from which ratings for E-diesel use could be varied. This would establish the 

RPN range corresponding to what might be considered acceptable as it reflects current 

practice. Table 4-3 is the result of this baseline diesel assessment, with failure modes 

ranked in order of decreasing RPN. 

As noted in the table, all failure modes for diesel fuel use have occurrence rankings of 

either 1 or 2, corresponding remote or low probability because the engine is designed to 

operate on specification diesel fuel and delivery of off-specification fuel, while it 

occurs, does so infrequently. Effects having to do with decreased engine power due to 

off-specification fuel viscosity have negligible to low severity (rating of 1) because 

variations in fuel viscosity likely to occur would result in potential maximum power 

output changes that would likely not be noticed. Effects associated with reduced life of 

easily replaced parts were given severity rankings of low (2). These were felt to be 

associated with only some annoyance. However, effects associated with the inability of 

the engine to operate, the replacement of difficult to replace parts such as fuel injectors, 
Table 4-2. Potential Performance Failure Modes 

Process: Fleet use of E-Diesel D

FMEA Process 

No. Item/Function 

Potential Failure 

Mode Causes of Failure O Effect(s) of Failure S Current Controls D RPN 

1 Fuel distributor 

fuel handling equipment 

Fuel handling line leaks 

Elastomer material degradation, hoses, seals, gaskets, O rings 

Fuel leaks and potential spills; replacement of subject parts 

Preventive maintenance and inspection 

2 Fleet operator 

fuel dispenser 

Fuel handling line leaks 

Elastomer material degradation, hoses, seals, gaskets, O rings 

Fuel leaks and potential spills; replacement of subject parts 

Preventive maintenance and inspection 

3 Engine Loss of power Lower fuel volumetric heating 

value 

Maximum engine power not achievable 

4 Engine Reduced thermal 

efficiency 

Changes in fuel properties Decreased fuel economy 

5 Engine Cold start problems Water in the fuel Inability to start 6 Engine Cold start problems Increased fuel cloud point Inability to start Block heaters, or 

continuous engine operation; fuel blending 

7 Engine Decreased durability Engine combustion chamber 

deposits/ corrosion 

Reduced time between required engine overhaul 

8 Fuel supply 

pump 

Vapor lock Higher fuel vapor pressure, supply 

pump cavitation 

 Engine stops running 

9 Fuel injector 

pump 

Fuel vaporization Local boiling due to high fuel 

vapor pressure 

Inconsistent power, engine stalls, hot start problems 

10 Fuel injector 

pump 

Increased pump internal wear 

Decreased fuel lubricity Reduced fuel pump life 

11 Fuel injector 

pump 

Fuel leakage Decreased fuel viscosity Maximum engine power not 

achievable 

12 Fuel injector 

pump 

Poor atomization of the fuel 

Decreased fuel viscosity Maximum engine power not 

achievable; decreased fuel economy; smoking 

13 Fuel filter Filter clogging Dispenser nozzle, fueling station 

and vehicle fuel tank and fuel system corrosion leading to solids in fuel line 

 Decreased fuel filter life 

14 Fuel filter Filter clogging Deposits in fueling station and 

vehicle fuel tank and fuel lines suspend into the fuel 

 Decreased fuel filter life 

15 Fuel injectors Injector clogging Fuel with mineral deposits, or fuel 

system corrosion 

 Decreased injector life 

16 Fuel injectors Injector clogging Off-specification fuel causes 

injector coking 

 Decreased injector life 

17 Fuel injectors Injector failure Corrosion of injectors - scouring of 

plunger and bushing 

 Decreased injector life 

18 Fuel line Fuel delivery system 

leaks - injector pumps and fuel line 

Elastomer material degradation, hoses, seals, gaskets, O rings 

Increased incidence of fuel leaks 
Table 4-3. Performance Risk FMEA Ratings for Diesel Fuel Use 

Process: Fleet use of Diesel D

FMEA Process 

No. Item/Function 

Potential Failure 

Mode Causes of Failure O Effect(s) of Failure S Current Controls D RPN 

5 Engine Cold start problems Water in the fuel 2 Inability to start 3 4 24 

16 Fuel injectors Injector clogging Off-specification fuel causes 

injector coking 

2 Decreased injector life 3 4 24 

18 Fuel line Fuel delivery system 

leaks - injector pumps and fuel line 

Elastomer material degradation, hoses, seals, gaskets, O rings 

2 Increased incidence of fuel 

leaks 

3 4 24 

13 Fuel filter Filter clogging Dispenser nozzle, fueling station 

and vehicle fuel tank and fuel system corrosion leading to solids in fuel line 

2 Decreased fuel filter life 2 5 20 

6 Engine Cold start problems Increased fuel cloud point 2 Inability to start 3 Block heaters, or 

continuous engine operation; fuel blending 

3 18 

8 Fuel supply 

pump 

Vapor lock Higher fuel vapor pressure, supply 

pump cavitation 

1 Engine stops running 3 5 15 

9 Fuel injector 

pump 

Fuel vaporization Local boiling due to high fuel 

vapor pressure 

1 Inconsistent power, engine 

stalls, hot start problems 

3 5 15 

2 Fleet operator 

fuel dispenser 

Fuel handling line leaks 

Elastomer material degradation, hoses, seals, gaskets, O rings 

1 Fuel leaks and potential spills; 

replacement of subject parts 

3 Preventive maintenance 

and inspection 

4 12 

7 Engine Decreased durability Engine combustion chamber 

deposits/ corrosion 

1 Reduced time between 

required engine overhaul 

3 4 12 

15 Fuel injectors Injector clogging Off-specification fuel with mineral 

deposits, or fuel system corrosion

1 Decreased injector life 3 4 12 

17 Fuel injectors Injector failure Corrosion of injectors 1 Decreased injector life 3 4 12 10 Fuel injector 

pump 

Increased pump internal wear 

Decreased fuel lubricity 1 Reduced fuel pump life 2 5 10 

14 Fuel filter Filter clogging Deposits in fueling station and 

vehicle fuel tank and fuel lines suspend into the fuel 

1 Decreased fuel filter life 2 5 10 

3 Engine Loss of power Lower fuel volumetric heating 

value 

2 Maximum engine power not 

achievable 

1 5 10 

1 Fuel distributor 

fuel handling equipment 

Fuel handling line leaks 

Elastomer material degradation, hoses, seals, gaskets, O rings 

1 Fuel leaks and potential spills; 

replacement of subject parts 

3 Preventive maintenance 

and inspection 

3 9 

12 Fuel injector 

pump 

Poor atomization of the fuel 

Decreased fuel viscosity 1 Maximum engine power not 

achievable; decreased fuel economy; smoking 

2 4 8 

4 Engine Reduced thermal 

efficiency 

Changes in fuel properties 1 Decreased fuel economy 1 5 5 

11 Fuel injector 

pump 

Fuel leakage Decreased fuel viscosity 1 Maximum engine power not 

achievable 

1 4 4 

4-4
4-5

and fuel spills were given severity ratings of moderate (3). These effects were felt to be 

associated with greater than minor annoyance. 

Few failure modes had current controls in place, so detection ratings were those for 

slightly effective or ineffective. Cold start problems could be prevented by fuel 

blending during periods of expected cold weather, continuous engine operation, or the 

use of block heaters. These would prevent the effect of the failure in most instances 

(detection rating of 3). Similarly, a preventive maintenance and inspection program at 

the fuel distributor would allow relatively frequent detection of elastomer material 

degradation in fuel handling lines leading to fuel leaks, so a detection rating of 3 was 

assigned. It was felt that a preventive maintenance and inspection program at the fleet 

vehicle fueling facility would be less effective. 

As noted in Table 4-3, the maximum RPN associated with diesel fuel use was 24. This 

serves as the baseline maximum risk for the reference situation and sets the standard for 

comparison for the FMEA of the performance risk of E-diesel use. The results of the 

initial FMEA rating of the same performance failure modes for E-diesel use are 

summarized in Table 4-4, again with failure modes ranked in order of decreasing RPN. 

In performing the performance FMEA of E-diesel use starting from the diesel fuel 

baseline, it was assumed that current controls were not changed. So neither severity nor 

detection ratings were changed; only occurrence ratings changed because of the 

replacement of diesel with E-diesel. 

The FMEA team believed that there was no reason to expect E-diesel use would have 

any effect on the probability of increased combustion chamber deposits, increased 

corrosion of fuel injectors, poor atomization of fuel into the cylinder, or fuel leakage in 

fuel pumps or injectors, so occurrence ratings for these failure/effects were not changed 

from the diesel fuel rating, and remained remote (1). There was no reference in the 

E-diesel literature that substantiated that any of these failures did indeed occur. 

Similarly, The FMEA team agreed that there was no reason to believe that using 

E-diesel instead of diesel would increase the frequency of cold start problems due to 

water in the fuel or increased fuel cloud point (which appears to occur via a different 

mechanism than diesel fuel clouding as noted above), injector coking, or elastomer 

degradation in the engine fuel line. Thus, these failure modes retained low occurrence 

ratings (2). Again, there was no reference in the E-diesel literature that substantiated 

that any of these failures became more frequent with E-diesel use. 

The frequency of some failure modes was increased from remote to low. These 

included: 

• Increased fuel pump internal wear due to decreased fuel lubricity; the rating was 

only increased to low because some blends include lubricity enhancers that would 

preclude this problem by increasing E-diesel lubricity to levels typical of diesel fuel 

• Reduced engine thermal efficiency due to changed fuel properties 

• Injector clogging due to mineral deposits or fuel system corrosion products 
Table 4-4. Initial Performance Risk FMEA Ratings for E-Diesel Use 

Process: Fleet use of E-Diesel D

FMEA Process 

No. Item/Function 

Potential Failure 

Mode Causes of Failure 

O Effect(s) of Failure S Current Controls 

D RPN 

3 Engine Loss of power Lower fuel volumetric heating 

value 

5 Maximum engine power not 

achievable 

2 5 50 

8 Fuel supply 

pump 

Vapor lock Higher fuel vapor pressure, supply 

pump cavitation 

3 Engine stops running 3 5 45 

9 Fuel injector 

pump 

Fuel vaporization Local boiling due to high fuel 

vapor pressure 

3 Inconsistent power, engine 

stalls, hot start problems 

3 5 45 

2 Fleet operator 

fuel dispenser 

Fuel handling line leaks 

Elastomer material degradation, hoses, seals, gaskets, O rings 

3 Fuel leaks and potential spills; 

replacement of subject parts 

3 Preventive maintenance 

and inspection 

4 36 

13 Fuel filter Filter clogging Dispenser nozzle, fueling station 

and vehicle fuel tank and fuel system corrosion leading to solids in fuel line 

3 Decreased fuel filter life 2 5 30 

14 Fuel filter Filter clogging Deposits in fueling station and 

vehicle fuel tank and fuel lines suspend into the fuel 

3 Decreased fuel filter life 2 5 30 

1 Fuel distributor 

fuel handling equipment 

Fuel handling line leaks 

Elastomer material degradation, hoses, seals, gaskets, O rings 

3 Fuel leaks and potential spills; 

replacement of subject parts 

3 Preventive maintenance 

and inspection 

3 27 

5 Engine Cold start problems Water in the fuel 2 Inability to start 3 4 24 

15 Fuel injectors Injector clogging Fuel with mineral deposits, or fuel 

system corrosion 

2 Decreased injector life 3 4 24 

16 Fuel injectors Injector clogging Off-specification fuel causes 

injector coking 

2 Decreased injector life 3 4 24 

18 Fuel line Fuel delivery system 

leaks - injector pumps and fuel line 

Elastomer material degradation, hoses, seals, gaskets, O rings 

2 Increased incidence of fuel 

leaks 

3 4 24 

4 Engine Reduced thermal 

efficiency 

Changes in fuel properties 2 Decreased fuel economy 2 5 20 

10 Fuel injector 

pump 

Increased pump internal wear 

Decreased fuel lubricity 2 Reduced fuel pump life 2 5 20 

6 Engine Cold start problems Increased fuel cloud point 2 Inability to start 3 Block heaters, or 

continuous engine operation; fuel blending 

3 18 

7 Engine Decreased durability Engine combustion chamber 

deposits/ corrosion 

1 Reduced time between 

required engine overhaul 

3 4 12 

17 Fuel injectors Injector failure Corrosion of injectors - scouring of 

plunger and bushing 

1 Decreased injector life 3 4 12 

12 Fuel injector 

pump 

Poor atomization of the fuel 

Decreased fuel viscosity 1 Maximum engine power not 

achievable; decreased fuel economy; smoking 

2 4 8 

11 Fuel injector 

pump 

Fuel leakage Decreased fuel viscosity 1 Maximum engine power not 

achievable 

1 4 4 

4-6
4-7

Several failure modes had their occurrence rating increased from remote or low (1 or 2) 

to moderate (3). These included: 

• Fuel distributor and fleet fueling station fuel handling line leaks due to elastomer 

degradation; the methanol fuel demonstration projects of the 1980s and early 1990s 

experienced such problems, which could be prevented with methanol-tolerant 

materials. It bears noting that ethanol should be much less aggressive to elastomers 

than methanol, and E-diesel, containing only 10 to 15% ethanol would be even less 

so. 

• Fuel filter clogging due to engine fuel system deposits becoming suspended because 

of the addition of ethanol to the fuel, or fueling station and engine fuel system 

component corrosion products becoming suspended in the fuel 

• Fuel supply pump or fuel injector pump loss of efficiency due to pump cavitation 

causing vapor lock or local fuel vaporization in injectors 

One failure mode had its occurrence rating increased from low (2) to certain (5). This 

was loss of engine maximum power because of the lower volumetric heat content of the 

E-diesel fuel. 

The performance risk ranking in Table 4-4 shows that the most significant failure mode 

rated was loss of engine maximum power, most heavily influenced by its certainty. Fuel 

supply pump and injector pump loss of efficiency due to cavitation or fuel vaporization 

in the injectors were the next highest ranked failures. Other failures ranked moderately 

high included fuel distributor and fueling station fuel handling line leaks due to 

elastomer degradation and fuel filter clogging due to suspension of engine fuel system 

deposits or fueling station and engine fuel system component corrosion. 

With respect to elastomer degradation, fleet demonstrations to date have not shown that 

major materials problems occur with E-diesel use (2, 3). However, these 

demonstrations have not covered all materials in all applications. Consequently the 

materials compatibility issue remains open until significantly more experience has been 

developed. 

4.2 Post-Action Revised FMEA Performance Impact Ranking 

As was done in the safety risk FMEA discussed in Section 3, after ranking the relative 

risk of the failure modes identified, the FMEA team identified recommended actions or 

process modifications for high ranked failure modes that will reduce the probability of 

the failure, mitigate its effects, or improve the process controls to enhance failure 

detection. In this evaluation, like the safety risk evaluation, only recommended actions 

that would reduce the frequency of occurrence were identified for high ranking failure 

modes. The FMEA team agreed that only these actions made sense, and that the 

severity of the effects could not be reduced nor could the probability of detection be 

fruitfully increased. The team defined recommended actions for failure modes in order 

of decreasing RPN beginning with the highest ranked failure mode, until a base RPN of 
4-8

24 was reached, that being the highest RPN for diesel use, and ostensibly a tolerable 

risk. 

Results of the definition of recommended actions, and the rated result the action would 

achieve are summarized in Table 4-5. As shown in the table, the loss in maximum 

engine power due to the decreased heat content of E-diesel fuel can be offset on a caseby-case basis by increasing the pumping capacity of the fuel injector pump(s). This 

could be done by either replacing the existing injection pump, or injectors on engines 

with unit injectors, with higher capacity models, or replacing the pump plunger with one 

that allowed higher capacity. Such an upfueling was done in at least one instance for a 

Cummins engine with a Bosch fuel pump (8). In this instance, the injection timing was 

not changed, so the net result of the pump upfueling was that the injection duration was 

increased (lengthened). This caused the engine’s brake thermal efficiency to decrease 

because, with an increased injection duration, the combustion interval in the cylinder 

extended to later in the engine cycle, leading to higher exhaust temperatures and an 

associated efficiency decrease. It would be possible to increase fuel injection capacity 

without changing either the timing or the duration of the injection cycle. This would be 

possible only on a case by case basis, as it would require a careful match of existing, 

available part combinations to engine applicability, however. Upfueling an engine’s 

fuel pumping capacity, even on only a volumetric flow (L/s) basis, might be considered 

to violate the engine’s Environmental Protection Agency (EPA) or California Air 

Resources Board (ARB) certification of engine regulated emissions. If so, this would 

require that the new combination be recertified. This would add to the expense of the 

action, which would already be relatively expensive if it involved replacing all the fuel 

injectors. 

The next most significant failure modes were decreased fuel supply pump or fuel 

injection pump efficiency due to cavitation causing vapor lock or localized fuel 

vaporization. The fuel supply pump cavitation problem could be addressed by installing 

an electric fuel pump at the vehicle fuel tank to replace the engine driven (usually gear) 

supply pump. This would remove the pump suction head that might lead to cavitation. 

The analogous fuel injector pump problem could be addressed with the electric fuel 

pump at the fuel tank and the addition of a restrictor fitting on the fuel return line to 

maintain sufficient fuel pressure at the injection pump(s) inlet. Doing these would 

decrease the occurrence rating for both failure modes to remote (1). 

The next four most significant failure modes in Table 4-5 could be addressed by 

replacing all susceptible fuel handling equipment at the fuel distributor, the vehicle fleet 

fueling station, and on the vehicle itself with E-diesel compatible materials. These 

actions would similarly lower occurrence ratings to the remote to low range (1 to 2). 

The methanol vehicle experience of the 1980s and early 1990s can be used as a valuable 

guide to ensure that compatible materials can be defined. 
Table 4-5. Revised Performance Risk FMEA Ratings for E-Diesel Use 

Process: Fleet use of E-Diesel Date: July 2

FMEA Process 

No. Item/Function 

Potential Failure 

Mode Causes of Failure 

O Effect(s) of Failure S Current Controls 

D RPN Act

3 Engine Loss of power Lower fuel volumetric 

heating value 

5 Maximum engine power not 

achievable 

2 5 50 Case by cas

system caparequire engin

8 Fuel supply 

pump 

Vapor lock Higher fuel vapor pressure, 

supply pump cavitation 

3 Engine stops running 3 5 45 Electric pum

replace engiprevents cavof suction he

9 Fuel injector 

pump 

Fuel vaporization Local vaporization due to 

high fuel vapor pressure 

3 Inconsistent power, engine 

stalls, hot start problems 

3 5 45 Electric pum

restrictor fittimaintain fueinjection pum

2 Fleet operator 

fuel dispenser 

Fuel handling line leaks 

Elastomer material degradation, hoses, seals, gaskets, O rings 

3 Fuel leaks and potential 

spills; replacement of subject parts 

3 Preventive maintenance 

and inspection 

4 36 Replace fue

components compatible m

13 Fuel filter Filter clogging Dispenser nozzle, fueling 

station and vehicle fuel tank and fuel system corrosion leading to solids in fuel line 

3 Decreased fuel filter life 2 5 30 Replace all c

diesel fueling vehicle with materials 

14 Fuel filter Filter clogging Deposits in fueling station 

and vehicle fuel tank and fuel lines suspend into the fuel 

3 Decreased fuel filter life 2 5 30 Replace all c

diesel fueling vehicle with materials 

1 Fuel distributor 

fuel handling equipment 

Fuel handling line leaks 

Elastomer material degradation, hoses, seals, gaskets, O rings 

3 Fuel leaks and potential 

spills; replacement of subject parts 

3 Preventive maintenance 

and inspection 

3 27 Replace fue

components compatible m

5 Engine Cold start problems Water in the fuel 2 Inability to start 3 4 24 

15 Fuel injectors Injector clogging Fuel with mineral deposits, 

or fuel system corrosion 

2 Decreased injector life 3 4 24 

16 Fuel injectors Injector clogging Off-specification fuel causes 

injector coking 

2 Decreased injector life 3 4 24 

18 Fuel line Fuel delivery system 

leaks - injector pumps and fuel line 

Elastomer material degradation, hoses, seals, gaskets, O rings 

2 Increased incidence of fuel 

leaks 

3 4 24 
Table 4-5. Revised Performance Risk FMEA Ratings for E-Diesel Use (concluded) 

FMEA Process 

No. Item/Function 

Potential Failure 

Mode Causes of Failure 

O Effect(s) of Failure S Current Controls 

D RPN Act

4 Engine Reduced thermal 

efficiency 

Changes in fuel properties 2 Decreased fuel economy 2 5 20 

10 Fuel injector 

pump 

Increased pump internal wear 

Decreased fuel lubricity 2 Reduced fuel pump life 2 5 20 

6 Engine Cold start problems Increased fuel cloud point 2 Inability to start 3 Block heaters, or 

continuous engine operation; fuel blending 

3 18 

7 Engine Decreased durability Engine combustion 

chamber deposits/ corrosion

1 Reduced time between 

required engine overhaul 

3 4 12 

17 Fuel injectors Injector failure Corrosion of injectors - 

scouring of plunger and bushing 

1 Decreased injector life 3 4 12 

12 Fuel injector 

pump 

Poor atomization of the fuel 

Decreased fuel viscosity 1 Maximum engine power not 

achievable; decreased fuel economy; smoking 

2 4 8 

11 Fuel injector 

pump 

Fuel leakage Decreased fuel viscosity 1 Maximum engine power not 

achievable 

1 4 4 

4-10
4-11

As noted in Table 4-5, by taking recommended actions, RPN ratings of formerly 27 to 50 

can be lowered to ratings of 9 to 20. Table 4-6 summarizes the results of the revised 

complete RPN ranking of failure modes after recommended actions have been taken. This 

revised ranking has a maximum RPN of 24, the same as for baseline diesel use, a risk rating 

considered acceptable. Thus, while E-diesel presents some potentially adverse process 

performance impacts, these can be mitigated by appropriate actions. Nevertheless, it bears 

keeping in mind that some mitigating actions may have unacceptable or unwarranted 

expense, and implementing these actions may still not result in the engine manufacturer 

extending warrantee coverage to vehicles using E diesel. 
T

able 4-6. Final Ranked Performance Risk FMEA Ratings for E-Diesel Use 

Process: Fleet use of E-Diesel Date: July 2

FMEA Process 

No. Item/Function 

Potential Failure 

Mode Causes of Failure O Effect(s) of Failure S Current Controls D RPN Act

5 Engine Cold start problems Water in the fuel 2 Inability to start 3 4 24 

15 Fuel injectors Injector clogging Fuel with mineral deposits, 

or fuel system corrosion 

2 Decreased injector life 3 4 24 

16 Fuel injectors Injector clogging Off-specification fuel causes

injector coking 

2 Decreased injector life 3 4 24 

18 Fuel line Fuel delivery system 

leaks - injector pumps and fuel line 

Elastomer material degradation, hoses, seals, gaskets, O rings 

2 Increased incidence of fuel 

leaks 

3 4 24 

13 Fuel filter Filter clogging Dispenser nozzle, fueling 

station and vehicle fuel tank and fuel system corrosion leading to solids in fuel line 

3 Decreased fuel filter life 2 5 30 Replace all c

diesel fueling vehicle with materials 

4 Engine Reduced thermal 

efficiency 

Changes in fuel properties 2 Decreased fuel economy 2 5 20 

10 Fuel injector 

pump 

Increased pump internal wear 

Decreased fuel lubricity 2 Reduced fuel pump life 2 5 20 

6 Engine Cold start problems Increased fuel cloud point 2 Inability to start 3 Block heaters, or 

continuous engine operation; fuel blending 

3 18 

8 Fuel supply 

pump 

Vapor lock Higher fuel vapor pressure, 

supply pump cavitation 

3 Engine stops running 3 5 45 Electric pum

replace engiprevents cavof suction he

9 Fuel injector 

pump 

Fuel vaporization Local vaporization due to 

high fuel vapor pressure 

3 Inconsistent power, engine 

stalls, hot start problems 

3 5 45 Electric pum

restrictor fittimaintain fueinjection pum

2 Fleet operator 

fuel dispenser 

Fuel handling line leaks 

Elastomer material degradation, hoses, seals, gaskets, O rings 

3 Fuel leaks and potential 

spills; replacement of subject parts 

3 Preventive maintenance 

and inspection 

4 36 Replace fue

components compatible m

7 Engine Decreased durability Engine combustion 

chamber deposits/ corrosion

1 Reduced time between 

required engine overhaul 

3 4 12 

17 Fuel injectors Injector failure Corrosion of injectors - 

scouring of plunger and bushing 

1 Decreased injector life 3 4 12 

4-12
Table 4-6. Final Ranked Performance Risk FMEA Ratings for E-Diesel Use (concluded) 

FMEA Process 

No. Item/Function 

Potential Failure 

Mode Causes of Failure 

O Effect(s) of Failure S Current Controls 

D RPN Act

3 Engine Loss of power Lower fuel volumetric 

heating value 

5 Maximum engine power not 

achievable 

2 5 50 Case by cas

system caparequire engin

14 Fuel filter Filter clogging Deposits in fueling station 

and vehicle fuel tank and fuel lines suspend into the fuel 

3 Decreased fuel filter life 2 5 30 Replace all c

diesel fueling vehicle with materials 

1 Fuel distributor 

fuel handling equipment 

Fuel handling line leaks 

Elastomer material degradation, hoses, seals, gaskets, O rings 

3 Fuel leaks and potential 

spills; replacement of subject parts 

3 Preventive maintenance 

and inspection 

3 27 Replace fue

components compatible m

12 Fuel injector 

pump 

Poor atomization of the fuel 

Decreased fuel viscosity 1 Maximum engine power not 

achievable; decreased fuel economy; smoking 

2 4 8 

11 Fuel injector 

pump 

Fuel leakage Decreased fuel viscosity 1 Maximum engine power not 

achievable 

1 4 4 
5-1

5. Conclusions 

The safety risk FMEA of the preparation, transportation, fleet vehicle fueling station 

storage, and use of E-diesel blends containing up to 15% ethanol in heavy-duty vehicle 

fleets concluded that, without fuel system infrastructure, fueling station, and vehicle 

modifications, E-diesel use poses significantly greater risk than diesel fuel or even 

gasoline use in comparable applications. All safety risks identified and ranked were 

risks of fire or explosion. These increased risks are due to E-diesel having the same 

flammability characteristics as ethanol. The most significant safety risks are associated 

with the possibility of explosion in storage and vehicle fuel tanks, and the potential for 

spilled fuel fires resulting from traffic accidents involving fuel transportation tankers or 

fleet vehicles. 

The safety risks can be mitigated by adopting many of the infrastructure and vehicle 

modifications employed in the methanol fueled heavy-duty vehicle demonstration 

programs performed in the 1980s and early 1990s, however. Recommended actions to 

reduce safety risks include: 

• Equipping all fuel storage tank vents and the vehicle tank vent and fill openings 

with flame arresters designed for use with ethanol 

• Ensuring that all fuel transfer processes including vehicle fueling incorporate 

effective vapor recovery systems 

• Establishing an electrical ground connection between the vehicle and the fueling 

station fuel dispenser 

• Insuring that vehicle fuel tank level detectors are of an intrinsically safe design 

By adopting these modifications, the relative risk of E-diesel use for most failure modes 

evaluated in the context of centrally-fueled fleet vehicle use becomes comparable to that 

for gasoline and diesel fuel use. This is the only E-diesel use scenario currently 

recommended. The most significant remaining risks are associated with spilled fuel 

fires resulting from traffic accidents. For these failure modes, the risk ranking exceeds 

that for diesel fuel use, but is comparable to that for gasoline fuel use. Additional 

actions could be taken to further reduce these fuel fire risks, such as automatic fire 

suppression systems. However, such systems are an expense likely not warranted. 

The performance FMEA for E-diesel use concluded that the loss of engine maximum 

power was the most significant adverse performance effect. This was followed by 

possible fuel pump cavitation causing vapor lock or fuel vaporization in injectors, and 

potential fuel filter clogging problems. Again, modifications can be made to address 

these possible adverse effects. These included: 

• Increasing the capacity of the fuel injection pump(s) on a case-by-case basis 

• Installing an electric fuel pump at the vehicle fuel tank and adding a restrictor fitting 

to the fuel return line 
5-2 

• Ensuring that all fuel handing system and vehicle engine fuel system components 

are of E-diesel compatible materials 

Taking these actions returns system performance to a level comparable to that for diesel 

fuel use. However, some of these actions may have unacceptable or unwarranted 

expense. 
R-1

References 

1. K. R. Gerdes and G. J. Suppes, “Miscibility of Ethanol in Diesel Fuels,” Ind. Eng. 

Chem. Res. Vol. 40, p 949, 2001. 

2. A. C. Hansen, P.W. L. Lyne, and Q. Zhang, “Ethanol-Diesel Blends: A Step 

Towards Bio-based Fuel for Diesel Engines,” ASAE Paper No. 01-6048, July 

2001. 

3. I. Ahmed, “E-Diesel : A U.S. Experience on the Development of 

Commercialization of Ethanol-based Fuels,” ISAF XIV Paper No. 2002-SM-06, 

November 2002. 

4. A. Rae, “E-Diesel : An Immediate & Practical Air Quality and Energy Solution,” 

ISAL XIV Paper No. 2002-EE-13, November 2002. 

5. U. Lofvenberg, “E-Diesel in Europe, a New Available Fuel Technology,” ISAF 

XIV Paper No. 2002-FT-31, November 2002. 

6. K. C. Corkwell and M. M. Jackson, “Lubricity and Injector Pump Wear Issues 

with E-diesel Fuel Blends,” SAE Paper No. 2002-01-2849, October 2002. 

7. R. L. McCormick and R. Parish, “Advanced Petroleum Based Fuels Program and 

Renewable Diesel Program, Milestone Report: Technical Barriers to the Use of 

Ethanol in Diesel Fuel,” NREL Report MP-540-32674, November 2001. 

8. M.C. Mendoza and P. V. Woon, “E-diesel Effects on Engine Component 

Temperature and Heat Balance in a Cummins C8.3 Engine, SAE Paper No. 2002-

01-2847, October 2002. 

9. N. Marek and J. Evanoff, “Pre-Commercialization of E-diesel Fuels in Off-Road 

Applications,” Proceedings of A&WMA 2002 Annual Conference, Paper No. 

42740, June 2002. 

10. R. E. McDermott, R. J. Mikulak, and M. R. Beauregard, The Basics of FMEA, 

Productivity, Inc., Portland, OR, 1996. 

11. L. Browning, C. Powars, E. Devino, M. Montano, and S. Unnasch, “Development 

of a Universal Fuel Formulation for Use in both Light and Heavy Duty Vehicles,” 

Acurex Environmental Final Report 96-115 prepared for NREL under Contract 

YCF-5-15106-01, November 1996. 

12. P. A. Machiele, “Methanol Fuel Safety: A Comparative Study of M100, M85, 

Gasoline, and Diesel Fuel as Motor Vehicle Fuels,” EPA-AA-SDSB-90-01, 

November 1990. 

13. P. F. Schmidt, Fuel Oil Manual, Industrial Press, Inc., New York, 1969. 
R-2 

14. M. J. Murphy, “Properties of Alternative Fuels,” UMTA-OH-06-0056-91-9, 

December 1991. 

15. N. Weyandt and M. L. Janssens, “Flame Arrester Evaluation for E-diesel Fuel 

Tanks,” NREL Report SR-540-34301, June 2003. 

16. ASTM Specification D 975. 

17. Personal communication (E_DieselAnalysis.xls), R. McCormick, NREL, June 

2003. 

18. R. M. Estafan and J. G. Brown, “Evaluation of Possible Methanol Fuel Additives 

for Reducing Engine Wear and/or Corrosion,” SAE Paper No. 902153, October 

1990. 
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Safety and Performance Assessment of Ethanol/Diesel Blends (E-Diesel) 

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L.R. Waterland, S. Venkatesh, and S, Unnasch 

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Subcontract report discussing safety concerns of ethanol-diesel blends and pathways to reducing risks. 

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