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The overall forest products industry is, for the purposes of environmental analysis, best divided into two major parts, depending on the fate of the harvested material. If the basic chemical integrity of the wood is maintained intact, to take advantage of its mechanical properties, we will refer to the associated industry sectors as the "wood products" sector. If the basic components of the wood are chemically separated, generally to isolate the specific properties of the cellulosic (fiber-forming) component, we will refer to to the associated sectors according to the nature of the final product. One of the most important of the latter group, the pulp and paper sector, is the subject of a separate analysis in this series. In this document, the focus will be on the wood products sector. In principle, the designation would include both the upstream component (logging and related activities) as well as the downstream sectors (manufacturing of specific wood end products). However, since environmental logging and timber management issues are not regulated by EPA, this analysis will concentrate on the manufacturing end of the chain.
The wood products sector is a significant source of volatile organic compounds (VOCs), which are important precursors of ground level ozone and "smog". Although the sector is a significant consumer of energy, its greenhouse gas impact is partially mitigated by the fact that much of the energy used in the sector is derived from scrap wood, rather than fossil fuels. Wood represents carbon which has been pulled from the atmosphere in recent times, so its re-release during combustion can be considered to be a recycling of existing carbon dioxide, instead of a net addition to the planet's greenhouse gas inventory. Burning scrap wood is also a beneficial use of what would otherwise be a solid waste. Thus, the VOC component represents the most significant impact from the sector.
Environmental impacts and risks
Effects of existing and future regulations on impacts
To understand the impacts of the wood products industry, it helps to understand the chemistry of wood. Woody plants evolved to serve three fundamental design challenges: to raise the plant's leaves above that of its neighbors (outcompeting them for sunlight), to withstand the increasing side loadings from storm winds that greater height entails, and to continue to transport fixed carbon products down to the roots and soluble nutrients up to the leaves efficiently, even as the distance between them increases.
The solution to these problems involved the development of a strong, fibrous structure running along the length of the trunk, composed of long strands of a biopolymer, cellulose (a polymer of sugar), and a tough, chemically stable cross-linking material, lignin, to tie the fibers together. The fibers form the tubes used for nutrient transport, and give the material very high tensile strength, while permitting enough side-to-side flexibility to allow the trunk to deflect the force of storm winds partially by changing the silhouette it presents to them. The cross links maintain the mechanical integrity and three dimensional shape of the fiber bundles.
The different impacts of the downstream industries making use of this material follow directly from the properties of the its constituents. The paper industry, needing the properties of the fibers without the cross-links, must isolate the fibers by chemically decomposing the lignin. Since one of the fitness properties shaping lignin's evolution was its ability to resist decomposition by natural chemical processes, the chemistry understandably involves constituents (such as reduced sulfur compounds) for which nature has not provided a means of disposal through a natural cycle. Paper mills (particularly pulp mills, where the separation of lignin from cellulose primarily takes place) accordingly produce relatively large quantities of problematic effluents.
In contrast, the wood products industry, which takes advantage of the mechanical properties of wood, preserves the composition, and thereby avoids most of the chemistry. The impact is accordingly significantly lower than that of the paper sector. Further mitigation of the waste stream from the wood products industry is possible because of another property of wood -- its use as a fuel. Burning of wood scraps can supply much of the process steam needed for plant operation, substituting a source of recently fixed carbon for fossil fuel, and thus reducing the impact of greenhouse gas emissions that would otherwise arise from the sector's energy needs.
However, while the wood products sector has less of an overall impact in most measures than the paper sector, its emissions of volatile organic compounds (VOCs) are in the same league as paper, and in fact are sufficient to make the wood products industry one of the top four of all sectors in overall VOC emissions. The heating of wood, a common operation when the wood must be dried for downstream applications, releases methanol. In addition, some wood products involve resins that release formaldehyde when cured. Reduction of VOC emissions from wood products manufacturing would represent the most significant opportunity for improving the environmental impact of this sector.
The wood products sector can be subdivided into producers of lumber, of various wood derivatives, such as plywood, particle board, and fiber board, and of finished wood products such as cabinets and containers. Another distinct subcategory comprises manufacturers who apply various wood preservatives to produce a material that resists degradation by molds and insects, even under conditions of high humidity, or when the wood is in contact with soil or water.
The top level NAICS and SIC classifications for the wood products sector are summarized below:
Wood furniture is classified as a sector in its own right, included in the NAICS scheme under category 337 (Furniture and related product manufacturing), and in the SIC scheme under category 25 (Furniture and fixtures). In both cases, wood furniture is not broken out as a single subcategory, but appears scattered in lower level subcategories among higher level subdivisions according to market segment (e.g. household furniture, office furniture, etc.).
Wood Products Council, comprising seven member organizations:
Certain key criteria air pollutant and hazardous air pollutant emissions from the wood products sector, broken down by SIC code at the four digit level, are summarized below. For comparison, the figures for the upstream processes (logging) have also been included. The subsectors are tabulated in order of VOC emissions, highest to lowest. Since the numbers are not normalized, the order reflects the total volume of material processed by each subsector as much as it does the inherent impact of the manufacturing processes involved. Per unit of production, processes that involve binding resins and drying of wood with relatively intense heat, such as the manufacture of composition board, will involve a higher level of emissions than simple sawing and planing, but the total amount of material produced by the latter causes it to outweigh the former in relative impact.
Air pollutant emissions from wood products facilities, in tons per year
VOC, NOx, and PM2.5: 1999 data from the National Emission Trends (NET) database
HAPs: 1996 data from the National Toxics Inventory (NTI) database
| SIC and description | VOC | NOx | PM2.5 | HAPs |
| 2421 - Sawmills & Planing Mills General | 24,873 | 14,442 | 15,787 | 776 |
| 2436 - Softwood Veneer And Plywood | 18,630 | 6,602 | 8,327 | 1,299 |
| 2493 - Reconstituted Wood Products | 16,770 | 10,922 | 7,398 | 2,220 |
| 2434 - Wood Kitchen Cabinets | 9,772 | 347 | 311 | 6,874 |
| 2499 - Wood Products, NEC | 8,852 | 1,743 | 1,567 | 4,636 |
| 2431 - Millwork | 8,520 | 314 | 750 | 1,560 |
| 2426 - Hardwood Dimension & Flooring | 4,836 | 693 | 1,880 | 196 |
| 2435 - Hardwood Veneer And Plywood | 2,926 | 709 | 852 | 482 |
| 2492 - Particleboard(1977) | 1,996 | 590 | 260 | |
| 2439 - Structural Wood Members, NEC | 1,247 | 275 | 292 | 1,008 |
| 2491 - Wood Preserving | 910 | 257 | ||
| 2451 - Mobile Homes | 712 | 5 | 60 | 550 |
| 2429 - Special Product Sawmills, NEC | 210 | 56 | 171 | 2 |
| 2452 - Prefabricated Wood Buildings | 202 | 4 | 9 | 98 |
| 2411 - Logging | 172 | 43 | 108 | |
| 2449 - Wood Containers, NEC | 92 | 16 | 57 | 2 |
| 2441 - Nailed Wood Boxes And Shook | 26 | 96 | 35 | 9 |
| 2448 - Wood Pallets And Skids | 11 | 35 | 96 | 11 |
| Other | 4 | 421 | 377 | 82 |
| Total | 100,761 | 37,313 | 38,337 | 20,062 |
Greenhouse gas emissions from a number of energy-intensive sectors have been calculated by NCMS on the basis of 1998 fuel consumption data from the Energy Information Administration (EIA) of the U. S. Department of Energy, and from greenhouse gas inventory data from the EPA (Inventory of U.S. Greenhouse Gas Emissions and Sinks). The results are posted in a summary document, Greenhouse Gas Estimates for Selected Industry Sectors. According to that calculation, the wood products sector was responsible for 36.5 Tg CO2 equivalent (1 Tg, or teragram = 1 million metric tons). This is a significant contribution, but well behind the impact of other sectors such as electric power (1,941.2 Tg CO2 equivalent) and paper (198.8 Tg CO2 equivalent). The EIA numbers also do not distinguish between fossil and "recent" carbon, so the net impact of the wood products sector on total atmospheric CO2 is somewhat less than the 36.5 Tg CO2 equivalent figure would indicate.
A Progress Report issued by the American Forest and Paper Association (AF&PA) in December, 2002 lists a number of industry benchmarks, based on 1999 data from its members. Among the benchmarks listed are:
The major environmental risk associated with the impacts from the wood products sector is the generation of ground level ozone, primarily from the VOC emission, and secondarily from the NOx emission. The severity of this type of emission for any given facility is strongly dependent on geographical and climate factors.
Given the fact that the primary impact from this sector is through air emissions, it is not surprising that most of the regulatory activity affecting the sector is occurring in the air quality area. Significant developments are noted below.
An Effluent Limit Guideline (ELG) for Timber Products Processing appears in Title 40 of the Code of Federal Regulations, Chapter 1, Part 429.
There are six categorical RCRA hazardous wastes from wood preserving operations:
The December, 2002 Progress Report from the American Forest and Paper Association (AF&PA) is a good source of environmental performance information for AF&PA member companies. (It also includes health and safety data.) It is available at http://www.afandpa.org/iinfo/environment/EHSpg01.pdf
The EPA Office of Enforcement and Compliance Assurance (OECA) has prepared a Sector Notebook on the Lumber and Wood Products Industry, available at http://www.epa.gov/compliance/resources/publications/assistance/sectors/notebooks/lmbrwdsn.pdf
"Forest products" is one of the Department of Energy Office of Industrial Technologies (DoE-OIT) "Industries of the Future". The DoE-OIT website at http://www.oit.doe.gov/forest/ provides:
A summary of toxic materials used in wood preserving can be found at http://es.epa.gov/techinfo/facts/preserve.html