Wood preservation facilities, general recommendations: chapter A-5


5. Description of Preservative Applications and Potential Chemical Discharges at Wood Preservation Facilities

The type and amount of chemical discharges from wood preservation facilities will be dependent on the design of the plant, the type of preservative(s) being applied, the sequences of the process and the operational practices in place. In order to identify, assess and evaluate the risk of exposure of workers and the potential chemical discharges from the facility, it is important to document and maintain a process plan and detail descriptions of each process. This chapter provides an overview of the common treatment process of a typical wood preservation plant.

5.1 Description of Process

A conceptual diagram should be prepared and maintained to document the wood treatment facility and its process flow of the fluid and pesticide. Examples are provided in Figure 1 of each preservative-specific chapter and in Figure 3, 4 and 5, Section 2.2.3 of Part 1 - General Background Information.

Detail descriptions should be included for each step of the process, such as the following:

  • Delivery and receiving of raw materials and primary products (e.g. wood, preservatives, other products)
    • Access point
    • Schedules of delivery
    • Delivery format (e.g. liquid concentrate, bags, drums)
    • Unloading drums, totes, concentrates, bulk, or solid preservative or constituents
      • Equipment used, manipulation of the concentrates
      • Safety measures, personal protective equipment (PPE), alarms, catchment, lighting...
    • Wood unloading method
    • Preservative storage
    • Size of machinery
    • ...
  • Wood conditioning
    • Dryers
    • Storage area
    • Sorting, piling and strapping area
    • ...
  • Preparing work solutions
    • Unloading concentrates from drums, crates, bags...
    • Chemical mixing
    • Machinery / Equipment required
    • Equipment elements (valves, opening access, engine...)
    • ...
  • Preservative application
    • Machinery required
    • Equipment requirement
    • Equipment elements (valves, opening access, engine,...)
    • ...
  • Quality assurance / quality control
  • Removing treated charges from cylinders
  • Methodology for fixation or stabilization
  • Handling treated lumber
  • Handling and maintaining any contaminated equipment
  • Storage of treated product
  • Recuperation system
  • Cleaning cylinders, kiln, fixation chambers or storage tanks
  • Waste storage and handling
  • ...

Technical information related to the treating process should also be documented:

  • Typical preservative retention in the wood product and variation on associated methodology
    • By species (spruce, fir, pine...)
    • By dimensions
    • By wood moisture content
    • ...
  • Maintenance and /or possible modification to existing equipment
    • Welding
    • New type of material
    • ...
  • Sampling procedures
  • Laboratory procedures
  • If a preservation facility is using more than one preservative, appropriate precautions should be taken and strictly followed. This might include the following:
    • Complete flushing of one preservative from cylinders, piping and sumps before introduction of the second preservative
    • Modification of procedures and training update
    • ...
  • ...

If a preservation facility is using more than one preservative, it is important that the procedures of the change over from one preservative to the other be well defined and documented.

This may include, but is not limited to, the following:

  • Use of other equipment
  • Blocking access to equipment (safety or contamination purposes)
  • Adding a complete flushing of one preservative from cylinders, piping and sumps before introduction of the second preservative
  • Colour coding pipes, containers and/or specific area for different preservatives
  • Review and maintenance of necessary PPE
  • Review of security measures and equipment
  • Procedures, training
  • ...

5.2 Potential Chemical Discharges

Potential chemical discharges could occur to water, air or soil, as well as possible transfers to material or equipment depending on the plant design and operational procedures. The discharge can vary in quantity and in state (e.g. gaseous, liquid or solid).

At every major step of the process, an analysis should be done to identify the potential sources. It should factor in normal operation conditions, extreme operating conditions and potential accidents that may occur.

Potential discharges that should be considered include the following:

Liquid Discharges

Preservatives and its process chemicals require water or other liquid as a solvent. Due to the toxicity and cost of the preservatives or process chemicals, ideally the facility should use closed loop treatment systems that contain, collect and reuse the chemical mixture to the greatest possible extent.

Closed systems may include the following types of equipment:

  • paved or concrete containment surfaces
  • dyking of major process components including the cylinder and tanks
  • containment surfaces for chemical drips from treated wood in storage, stabilization/fixation, or drying areas
  • collection sumps to receive residual preservative
  • cartridge filters to remove dust and wood debris from contaminated liquids entering the system
  • holding tanks for filtered solutions
  • ...

Some liquid streams that may not be possible for re-use include the following:

  • condensates removed from the wood during conditioning or vacuum application
  • condenser cooling water
  • water released by the wood during the treatment cycle
  • washwaters for oil-borne facilities
  • spills, overflows and leaks
  • stormwater runoff from unpaved or unroofed areas or yard soil contamination
  • spills from hose ruptures during the unloading of trucks
  • spills from piping failure
  • spills from damage of waste drum
  • drippage from lumber that was removed from the drip pad too soon
  • ...

All attempts should be made to re-use these streams in the treating process, however, if this is not possible the streams must be treated prior to discharging to natural environment. In addition, the liquid discharges may be subjected to certain conditions, limits or requirements that are enforced by the local, provincial and federal authorities

Solid Wastes

Solid waste generation at wood preservation facilities may include the following:

  • cartridge filters and traps
  • broken treated wood
  • sludge from tanks, sumps, fixation/stabilization chambers/kilns and pressure cylinders
  • sludge from wastewater treatment processes
  • contaminated soils
  • containers, wrappings, wood lath, stickers and pallets
  • dust, sawdust, debris
  • ...

Air Emissions

Potential sources of air emissions include the following:

  • exhausts, mists and vapours from kilns
  • exhausts, mists and vapours from tank vents
  • mists and vapours from vacuum pump exhausts
  • mists and vapours from opening of retort cylinder doors and tank hatches
  • vapours from freshly treated charges
  • exhausts, mists and vapours from stabilization kiln or accelerated fixation process
  • ...

Section 9 provides additional information on air-emissions control and discharge disposal.

The conceptual diagram mentioned in 5.1 that identifies the potential release points from the process could be used for training purpose.

Activities are usually analyzed individually. Other potential risks may arise when activities are analyzed in conjunction with multiple simultaneous activities. A review of the conceptual diagram with dynamic activities in mind may help identify other potential chemical discharges.

In case of accidental releases, prompt containment or emergency procedures should be applied and appropriate authorities should be contacted promptly (see Section 12 - Environmental Emergency Notification and Contingency Planning).

5.3 Potential Effects of Chemical Discharges

The actual impact of any liquid discharge, solid waste or air emission depends on many factors, including:

  • the location of the facility relative to ground or surface waters
  • the location of the facility to potential receptors
  • the amount released
  • the frequency of releases
  • contingency measures in place at the facility.

Variables that may affect the health and safety of the workers at the wood preservation facility include:

  • Ambient concentrations
  • Ambient conditions
  • Frequency of exposure
  • Duration of exposure
  • Availability, usage and effectiveness of the protective measures during period of exposure.

Information about the potential health or environmental effects are provided by:

  • Health Canada‚Äôs Pest Management Regulatory Agency (PMRA)
  • Office of Pesticide Programs (United States Environmental Protection Agency)
  • National Research Council of Canada
  • World Health Organization
  • International Labour Organization
  • Environment Canada
  • Chemical suppliers
  • Consultants
  • Industrial hygienists

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