ncasi    January 15, 2014 

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The Air Emissions Impact of Burning Railroad Tie-Derived Fuel 

Introduction 

Wood is treated with creosote when preparing railroad cross ties (railties) in order to prolong the useful 

life of the ties by protecting them against insect and fungal attack. Wood exposed to the outdoor 

atmosphere and in direct contact with soil or water is more prone to decay and therefore usually requires 

treatment. At the end of their useful life, treated wood products like railties must be landfilled, reused 

beneficially, or burned for energy recovery. This paper summarizes available information on the air 

emission impact of burning railties in industrial boilers, specifically those equipped with stokers. A full 

comparison of the contaminants (trace metals, organics, etc.) in railties with those in traditional fuels such 

as coal, biomass and fuel oil was carried out earlier and submitted to EPA in support of the NonHazardous Secondary Material (NHSM) rule (AF&PA 2013). 

A. Testing at an Electricity Generating Unit (EGU) at McBain, MI 

Under EPA’s supervision, elaborate emission tests were conducted on the Viking Energy, McBain, MI 

wood-fired stoker (with ESP) when burning chipped creosote-treated railties and several other treated 

wood wastes (EPA 1994). The test results for chipped creosote-treated railtie burning are summarized in 

Table 1. The boiler typically fired about 600 tons per day of virgin and recycled untreated wood in chip 

form. However, a baseline run with 100% untreated wood was not conducted during this study. Table 1 

provides a comparison of the mean emissions when firing railties in the McBain boiler against ranges 

and/or means of emissions from firing 100% untreated wood residues in stoker units with ESPs, the latter 

being obtained from Boiler MACT and other recent test data that were summarized in NCASI Technical 

Bulletin No. 1013 (NCASI 2013). Sampling was conducted for dioxins/furans (PCDD/Fs), several 

polyaromatic hydrocarbons (PAHs), trace metals, particulate matter (PM), HCl, formaldehyde, acrolein, 

NOx, CO, SO2 and VOCs. 

A comparison of emissions resulting from burning 29.0 wt% creosote-treated wood (remainder being 

virgin and recycled untreated wood) in the Viking boiler with emissions from burning 100% untreated 

wood residues in stoker units (NCASI 2013) indicates that there is no discernible difference due to the 

addition of railties to the untreated wood fuel. In fact, most emissions when burning creosote-treated 

wood are lower than the averages for 100% wood burning, including those of PAHs. Emissions of 2-

methylnaphthalene from 29% creosote substituted wood burning were comparabale to the maximum 

values from untreated wood burning. However, the emissions of all other PAHs were closer to the lower 

end of the range. (NCASI 2005, 2013). This observation is not surprising given that PAH emissions 

reduce when the robustness of combustion increases. The use of dry fuels with high heat value, like 

railties, generally improves combustion, thereby reducing products of incomplete combustion like PAHs. 

 
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Table 1. Trial Burns of Creosote-Treated Railties in a Wood-Fired Boiler (EPA 1994) 

 Baseline CreosoteUntreated Wood1 Treated2, 3 

Range Mean 

Co-firing Rate (% wt) 29.00 

Load (lb/hr steam) 157,990 

Dioxins (ng/m3

)

4

 0.0017 to 0.375 0.164 

PAHs (ng/m3

) 

Naphthalene 14 to 599,295 917.2 

2-Methylnaphthalene 50 to 3,679 3,704 

Acenaphthene 3 to 10,214 67.7 

2-Chloronaphthalene 2.955 1.29 

Acenaphthylene 11 to 38,517 38.1 

Fluorene 4 to 32,857 145.4 

Phenanthrene 11 to 43,071 499.1 

Anthracene 4 to 32,857 30.4 

Fluoranthene 7 to 13,044 87.0 

Pyrene 7 to 32,857 49.9 

Benzo(a)anthracene 1 to 445 2.5 

Chrysene 3 to 619 2.56 

Perylene 1 to 110 0.53 

Trace Metals (μg/m3

) 

Arsenic 0.2 to 11.5 ND 

Cadmium 0.09 to 1.66 ND 

Chromium 0.12 to 11.6 ND 

Copper 3.13 to 13.55 13.8 

Lead 0.44 to 35.6 ND 

Mercury 0.1 to 8.2 0.68 

Nickel 0.24 to 18.2 ND 

Zinc 20.6 to 8725 87.8 

 Mean Mean

Part. Matter (gr/dscf) 0.0295 0.0087 

HCl (mg/m3

) 5.37 ND 

Formaldehyde (μg/m3

) 1,255 76.0 

Acrolein (μg/m3

) 320 ND 

NOx (ppm) 136 168 

NOx (lb/106

 Btu) 0.21 0.23 

CO (ppm) 765 120 

SO2 (lb/106

 Btu) 0.011 0.027 

VOC (ppm) 11.0 0.8 

 1

NCASI TB 1013 - factors available for 100% wood combustion in a stoker unit with ESP in units of lb/MMBtu were converted 

assuming F factor of 9,280 dscf @ 0% O2/106

 Btu, 6% O2 in stack and 8,400 Btu/lb dry wood; 2concentrations for the McBain 

unit are expressed at stack O2 which varied from 4 to 5%; 3

29% creosote-treated wood, remainder untreated and recycled wood; 4

mass (not TEQ) basis; 5same as AP-42 Chapter 1.6 
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B. Pilot-Scale Tesing of Creoste-Treated Wood With Coal 

Freeman et al. (2002) conducted a pilot-scale study co-firing creosote-treated woods with coal to provide 

data for pre-permitting evaluations by utilities interested in co-firing biomass as a means of increasing 

renewable energy use. The results of these tests are summarized in Table 2. Substances tested for 

included PCDD/Fs, PAHs, several heavy metals, formaldehyde and other VOCs, HCl and particulates. 

These emissions represented “uncontrolled” emissions from the combustor “upstream of flue gas cleanup 

devices.” 

From the results presented in Table 2, the authors concluded that creosote-treated wood could be 

successfully co-fired in coal-fired utility boilers at 10% heat input without increases in most air toxic 

emissions relative to the baseline with 100% eastern bituminous coal firing. Compared to the baseline test 

results with 100% coal, the results with 10% creosote-treated wood (rest coal) consistently showed lower 

levels (often non-detectable) of dioxins/furans, PAHs, heavy metals, formaldehyde and other aldehydes, 

ketones and total hydrocarbons. The slightly higher levels of HCl emissions measured (61 vs 44 ppm) 

appears to be an anomaly since creosote-treated wood has much lower chlorine levels than most coals, 

being similar to those in virgin wood fuels (<0.07%). 

Table 2. Emissions from Creosote Treated Wood Cofiring with Coal (Freeman et al. 2002) 

Baseline

UF Coal 

10% Creosote 

Wood1 

 

Flue Gas (dry basis @ 3% O2)

SO2 (ppm) 1209 1120 

NOx (ppm) 574 474

CO (ppm) 92 75

HCl (ppm) 44 61

Total Hydrocarbons (ppm)

2 2.0 1.6

Particulate (g/dNm3

) 8.9 5.5

VOCs (dry basis @ 3% O2))

Acetaldehyde (ppb) <1.4 <2.7

Acetophenone (ppb) <1.5 <1.2

Formaldehyde (ppb) ~2.3 2.4

Isophorone (ppb) <0.21 <0.18 

Propionaldehyde (ppb) <0.53 <0.46 

PCDD/Fs (ng/dNm3 @ 3% O2)

Total PCDD/Fs 0.0463 0.0039 

WHO TEQs 0.0014 ND

Total PAHs (μg/dNm3 @ 3% O2) 0.134 0.079 

Heavy Metals (g/MJ)

Antimony 7.36E-06 6.38E-06 

Arsenic 4.21E-04 3.42E-04 

Cadmium 5.84E-06 4.65E-06 

Cobalt 2.38E-04 1.14E-04 

Lead 1.34E-04 9.96E-05 

Manganese 1.17E-03 6.68E-04 

Mercury 9.18E-06 9.40E-06 

Nickel 2.01E-04 1.23E-04 

Selenium 6.61E-05 3.96E-05 

1

 10% creosote treated wood, remainder coal; 2 as propane; ND – non-detect 
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C. Chipped Railroad Tie Burning in a Pulp Mill Bark Boiler 

In 2003, a southwestern pulp mill conducted extensive tests on its bark boiler by replacing the entire 

wood fuel with chipped railroad ties. The boiler was tested with 100% railties for several criteria 

pollutants, particulate matter (PM), six trace metals (As, Cd, Cr, Pb, Cu and Zn), several semi-volatile 

organics (SVOCs), PCDD/Fs, and several speciated VOCs. CO, THCs, NOx and SO2 were also measured 

during a baseline test with 100% bark/wood residues (NCASI File Information). These emissions data are 

compared in Table 3. For comparison purposes, the emission data from this study are compared against 

mean and range of emissions when firing 100% untreated wood residues in stoker units with ESPs 

(NCASI 2013). Once again, the emissions data with 100% railtie combustion in a stoker unit are routinely 

lower than for 100% untreated wood combustion. 

Table 3. Criteria and Non-Criteria Pollutants From Burning Railties in a Bark Boiler 

 100% Bark 100% Untreated Wood

 Railties Range or Mean5

RTDF feed rate tons/hr 0 24.7

Steam KPPH 520 430 

CO ppm@8%O2 316 117 663 

THC as C ppm@8%O2 56 7 9.5 

NOx lb/MMBtu 0.20 0.21 0.21 

SO2 lb/MMBtu 0.00 0.01 0.011 

PM gr/dscf@7%O2 0.026 -- 

PCDD/Fs ng/dscm@7%O2 5.01E-041 7.21E-035

As μg/dscm@7%O2 11.0 0.2 to 11.5 

Cd μg/dscm@7%O2 4.8 0.09 to 1.66 

Cr μg/dscm@7%O2 5.8 0.12 to 11.6 

Cu μg/dscm@7%O2 45.2 3.13 to 13.56

Pb μg/dscm@7%O2 107.8 0.44 to 35.6 

Zn μg/dscm@7%O2 764.7 20.6 to 8726

SVOCs 

Naphthalene μg/dscm@7%O2 2.98 11.4 

Bis(2-ethylhexyl)phthalate μg/dscm@7%O2 1.90 0.1 

Benzyl alcohol μg/dscm@7%O2 4.10 No data 

Benzoic acid μg/dscm@7%O2 152.4 49.5 

All Others3 μg/dscm@7%O2 ND -- 

VOCs 

Methyl chloride μg/dscm@7%O2 9.34 628.0 

Chloroform μg/dscm@7%O2 19.97 23.1 

Benzene μg/dscm@7%O2 38.84 1125.0 

Toluene μg/dscm@7%O2 4.96 24.2 

Xylenes (total) μg/dscm@7%O2 4.04 6.0 

Ethyl Benzene μg/dscm@7%O2 1.35 453.5 

Styrene μg/dscm@7%O2 1.4 547.6 

All Others4 μg/dscm@7%O2 ND -- 1 I-TEF/89 units; 2

WHO-TEF 2005 units; 3 over a hundred other compounds including phenol, 1,2-dichlorobenzene, 1,2,4-

trichlorobenzene, 2,4,6-trichlorophenol, hexachlorobenzene, pentachlorophenol, and several PAHs; 4

over 50 other VOCs 

including chloromethane, vinyl chloride, carbon tetrachloride, 1,1,2-trichloroethane, trichloroethene, tetrachloroethylene; 5

NCASI TB 1013 - factors available for 100% wood combustion in a stoker unit with ESP in units of lb/MMBtu were 

converted assuming F factor of 9,280 dscf @ 0% O2/106

 Btu and 8,400 Btu/lb dry wood; 6same as AP-42 Chapter 1.6 

 
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The emissions of Cd, Cu, and Pb from 100% railtie burning were higher than the maximum values from 

untreated wood burning. However, it should be noted that emissions of PM and trace metals are generally 

a function of the PM control device efficiency. Unless the fuel combusted is believed to contain a 

particular trace metal in unusually large concentrations (not the case with railties), a comparison of 

resulting emissions should made with care as it ignores any variability in effectiveness of the control 

device. It is also worthwhile to note that the 100% railtie substitution scenario is a highly atypical worstcase boundary condition – railtie substitution levels in industrial boilers typically range between 5 and 

30%.

D. Emissions from Combustion of Railties in Several EGUs – A 1995 Study 

Holtzman and Atkins (1995) reported on air emissions data from the burning of railties in several large 

independent wood-fired power plants (EGUs) and one coal-fired plant (EGU). The treated wood 

emissions data from each of the test programs are also compared to emissions from combusting clean 

wood or coal in these boilers. The wood-fired EGUs ranged in size from 20 to 50 MW, were of a spreader 

stoker design, and had either a baghouse or ESP for PM control. Table 4 provides an emissions 

comparison between burning clean wood with and without various levels of railties at 3 different sites, 25 

to 50% railties at Site A, 20% railtie at Site B, and 10% railtie at Site C. The emissions measured included 

criteria pollutants PM, NOx, CO, SO2 and THCs, trace metals As, Be, Cd, Cr, Cu, Pb, Mn, Hg, Ni, Se and 

Zn, acid gases HCl and H2SO4, PCDD/Fs and several organics. The comparison clearly shows that 

burning railties at various levels in these stokers along with clean wood had no discernible bearing on the 

air emissions of most criteria and non-criteria pollutants (SO2 emissions continued to be negligible but 

were marginally higher; Among trace metals, only arsenic emissions were somewhat higher). 

 
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Table 4. Emissions Comparison of EGUs Burning Clean Wood With and Without Railroad Ties

Site A Site B Site C

Clean 25-50% Clean 20% Clean Wood 10% 

All emissions are in units of lb/MMBtu 

Particulate Control MC ESP MC ESP ESP ESP MC ESP MC ESP

Emissions Control

Heat Input (MMBtu/hr) 339 339 711 681 286 295

Particulate Matter 1.68E-03 1.31E-03 2.63E-02 2.80E-02

PM - Back Half 9.84E-03 3.94E-03 3.55E-03 6.27E-03

Nitrogen Oxides 1.44E-01 1.22E-01 2.08E-01 2.07E-01 1.96E-01 2.00E-01

Carbon Monoxide 2.65E-01 5.21E-01 4.30E-01 4.04E-01 2.68E-01 1.39E-01

Sulfur Dioxide 2.54E-03 4.07E-02 7.33E-03 2.08E-03 4.30E-02

Hydrocarbons 3.62E-03 5.72E-03 5.07E-03 3.62E-03

Arsenic 1.44E-07 7.97E-07 1.64E-05 3.07E-05

Beryllium <2.87E-07 <1.91E-06

Cadmium <2.87E-07 <1.53E-06 1.20E-06 1.29E-06

Chromium <6.37E-07 <2.87E-06 3.36E-05 4.09E-05

Hexavalent Chromium * Not Tested 1.62E-06

Copper 1.59E-05 3.51E-06

Lead 1.59E-05 1.12E-06 9.64E-06 2.20E-05

Manganese 3.01E-05 1.43E-06 8.59E-05 1.18E-04

Mercury 3.19E-07 4.30E-07

Nickel <2.87E-06 <1.34E-05 3.97E-06 1.98E-06

Selenium <2.87E-06 <3.62E-06 5.53E-07 4.36E-07

Zinc 1.12E-05 4.30E-06

Hydrogen Chloride 5.60E-05 5.60E-05

Sulfuric Acid 1.63E-02 2.25E-02

2,3,7,8-TCDD 7.80E-11 3.51E-11 1.66E-12 3.66E-12

Acetaldehyde 7.57E-05 2.54E-05 5.11E-04 1.54E-04

Acrolein 1.85E-04 5.74E-06

Benzene 2.45E-04 1.55E-04 2.18E-04 2.40E-04

Benzo(a)anthracene <5.00E-09 <6.00E-09 2.73E-07 2.82E-07

Benzo(a)pyrene <5.00E-09 <6.00E-09 2.98E-07 3.21E-07

Chlorophenols 1.94E-05 2.11E-05

Clorobenzenes 1.19E-05 1.28E-05

Chloroform <3.64E-05 <2.14E-05

Chrysene/Triphenylene <5.00E-09 <6.00E-09 2.98E-07 3.08E-07

Formaldehyde 2.800E-04 1.32E-04 2.36E-03 7.20E-04

Naphthalene 7.05E-06 3.28E-06

Phenol 2.27E-05 4.58E-06

Toluene <2.97E-05 <4.49E-05 2.29E-05 3.07E-05

Dioxins <6.48E-12 <1.83E-11

Furans <2.05E-11 <1.99E-10

*Blank indicates no data

 
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Table 5 provides an emissions comparison between burning coal with and without railties at low and 

high loads at a coal-fired EGU. The emissions measured included criteria pollutants PM, NOx, CO, and 

SO2, trace metals As, Be, Cd, total Cr, Cr+6, Cu, Pb, Hg, Ni, and Zn, acid gas HCl, PCDD/Fs, PCBs, 

PAHs, total chlorophenols, and formaldehyde. Once again, most emissions were comparable or lower as a 

result of co-firing railties in this coal-fired unit (formaldehyde and arsenic emissions were a bit higher). 

Table 5. Baseline and Railtie ombustion Emission Test Summary, Hickling Station, East Corning, NY 

 

 Low Load (lb/hr) High Load (lb/hr) 

Test Parameters Baselinec

 Creosote Treatedd Baselinec Creosote Treatedd

 

Total particulate 35.63 2.06 133.43 5.37 

Carbon monoxide (CO) 13.9 12.9 9.9 24.0 

Nitrogen oxides (NOx) 66.6 94.3 206.3 156.3 

Sulfur dioxide (SO2) 686.5 439.6 1436.6 724.5 

Arsenic (As) a a 1.72E-03 6.24E-02 

Beryllium (Be) a a <2.54E-04 <7.04E-04 

Cadmium (Cd) a a 4.52E-04 1.10E-04 

Total Chromium (Cr) a a 7.74E-03 5.90E-03 

Hexavalent Chromium (Cr+6) a a <4.08E-03 5.90E-04e

Copper (Cu) a a 8.56E-03 8.82E-03 

Lead (Pb) a a 3.24E-03 1.18E-03 

Mercury (Hg) a a 2.88E-02 1.33E-02 

Nickel (Ni) a a 2.58E-03b

 3.39E-04 

Zinc (Zn) a a 1.86E-02 3.31E-03 

Formaldehyde (HCHO) a a 0.012 0.028 

Hydrogen chloride (HC1) a a 48.7 13.44 

2,3,7,8 TCDD Tox. Equiv. a a 4.81E-09 1.696E-08 

Total PAHs 4.56E-04 <1.26E-02 6.44E-04b

 <2.12E-02 

Total PCBs a a <2.44E-05 <1.23E-03 

Total chlorophenols a a 9.17E-05 <2.42E-02 

 

Source: Unit 1 Creosote Treated Wood/Coal CO-Fired Feasibility Project 

a Indicates no source testing was conducted for these test parameters. 

b Estimated emission rate. When 1 or 2 of the 3 sample runs demonstrated emissions below the detection limit, 

 one-half of the detection limit for each of the ND test runs was used to calculate the average emission rate. 

c Baseline emissions (coal only) testing performed by Galson Corporation in June 1992. 

d Creosote treated wood testing performed by TRC Environmental Corporation in November 1993. 

e Chromium+6 values were calculated assuming 10% of total chromium was chromium +6.   

 
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Summary 

The data presented in this paper indicate that the air emission impact of burning creosote-treated railroad 

ties (railties) along with either virgin, untreated biomass or coal in stokers is not any different than that 

from the burning of untreated biomass or coal in these units. The organic constituents in the creosote 

appear to oxidize completely during combustion on the grate and above the grate in such boilers such that 

the emission of VOCs, SVOCs, PCDD/Fs and other products of incomplete combustion would be similar 

in magnitude as the baseline fuel. Further, the metals content of the railties are known to be similar to 

those in virgin wood fuels and thus the trace metals air emission impact of co-firing these fuels in a given 

boiler would be no different than those measured when firing predominantly untreated wood fuel in the 

same boiler. 

References 

AF&PA (American Forest & Paper Association) 2013. “Comparison of Contaminant Concentrations in 

Cross Tie-Derived Fuel with Traditional Fuels”, submitted to EPA on March 28, 2013 as Attachment A 

Freeman, M.C., O’Dowd, W.J., Brown, T.D., Hargis, R.A. Jr., James, R.A., Plasynski1, S.I., 

Walbert, G.F., Lowe, A.F., and Battista, J.J. Jr. 2002. Pilot-scale air toxics R&D assessment of 

creosote-treated and PCP-treated wood cofiring for pulverized coal utility boiler applications. 

http://www.netl.doe.gov/osta/techpapers/2002-710.pdf (accessed September 2005). 

Holtzman, M. I. and Atkins, R. S. 1995. Emissions from Combustion of Treated Wood Fuel and Tires in 

Industrial Boilers. Presented to the Air and Waste Management Association Annual Meeting, June 18-23, 

1995. 

National Council for Air and Stream Improvement, Inc. (NCASI). 2005. Alternative fuels used in the 

forest products industry: Their composition and impact on emissions. Technical Bulletin No. 906. 

Research Triangle Park, N.C.: National Council for Air and Stream Improvement, Inc. 

National Council for Air and Stream Improvement, Inc. (NCASI). 2013. A Comprehensive Compilation 

and Review of Wood-Fired Boiler Emissions. Technical Bulletin No. 1013. Research Triangle Park, N.C.: 

National Council for Air and Stream Improvement, Inc. 

Smith, S. T. 2002. Environmental Issues Related to the Use of Creosote Wood Preservative. AcuAeTer, 

Inc. Helena, MT (May 28, 2002) 

(http://home.earthlink.net/~stephentsmith/sitebuildercontent/sitebuilderfiles/Env-Issues.pdf)