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Remediation Technologies Screening Matrix, Version 4.0  
Chapter 23 Low-Temperature/High-Temperature Thermal Desorption
Table of Contents


23-2 Hazard Analysis

Principal unique hazards associated with low-temperature/high-temperature thermal desorption include:

Physical Hazards Chemical Hazards Radiological Hazards Biological Hazards

a. Physical Hazards

(1) Description: Desorption treatment units may expose workers to elevated noise levels in the work area due to the operation of air blowers, pumps, and the ignition of fuels within the combustion chamber. The noise level may interfere with safe and effective communications.

Control: The regulatory requirements of CEGS 02289 (Remediation of Contaminated Soils by Thermal Desorption) should be followed to address noise. Personal protective equipment (PPE) should include hearing protection. Personal electronic communications devices, such as a dual ear headset with speaker microphone, may be used to overcome ambient noise. The device reduces ambient noise levels while enhancing communication. Noise-free areas should be established during operations to provide breaks from the noise, which can cause fatigue and inattention. CONTROL POINT: Design, Operations

(2) Description: Thermal desorption units which are not operated below the ASTM E953 determined ash fusion temperature may cause the solid waste material to vitrify into a large hot mass within the unit. The resulting heat and pressure buildup may exceed the equipment pressure rating of the unit, possibly causing a fire or explosion and possible release of waste materials.

Control: Operation of the unit should follow the instructions in CEGS 02289, Remediation of Contaminated Soils by Thermal Desorption. This standard, in part, requires:

- A Startup Plan;

- A Proof of Performance Plan listing the proposed operating conditions for process parameters to be continuously monitored and recorded;

- An Operating Plan specifiying detailed procedures for continued operation of the system, based on the proof of performance results; and

- A Demobilization Plan.

CONTROL POINT: Design, Operations, Maintenance

(3) Description: Thermal desorption usually requires storage of flammable or combustible fuels (e.g. kerosene, waste fuels). Hazards associated with flammable/combustible fuels include the potential for on-site spills or release of material. The release may cause worker exposure to the vapors generated or a fire hazard may exist if the material is ignited.

Control: Consideration should be given to ensure that the type of tanks used are appropriate, equipped with pressure-relief devices, and are bermed to help prevent release of material to the work environment. The electrical equipment and fixtures should comply with NFPA 70. CEGS 02289 (Remediation of Contaminated Soils by Thermal Desorption) requires that fuel system installation/storage and testing comply with the applicable requirements of NFPA 30 (Flammable and Combustible Liquids Code), NFPA 31 (Installation of Oil Burning Equipment), NFPA 54 (National Fuel Gas Code), or NFPA 58 (Standard for the Storage and Handling of Liquefied Petroleum Gases), as appropriate to the type of fuel. The area should also be adequately ventilated to help prevent the accumulation of flammable vapors. Only trained and experienced workers should be permitted to work on the system. All electrical systems should be locked out and tagged out during repair or maintenance. CONTROL POINT: Design, Construction, Operations, Maintenance

(4) Description: During excavation of waste materials with low flash points, saturated soils may be ignited by sparks generated when the blade of the dozer or crawler contacts rocks or other objects. If the soil is to be crushed to the proper size prior to feeding into the desorption unit, waste materials with higher than expected BTU values may be ignited during the crushing/sorting process.

Control: The periodic application of water to the soils may help to control soils from being ignited. Periodic wetting of the soil before and during crushing may be necessary to prevent ignition. The soil handling equipment may also be equipped with non-sparking buckets or blades. CONTROL POINT: Operations

(5) Description: If the BTU value of the waste feed is not controlled and high BTU value feed enters the desorption unit, the temperature of the unit may exceed design specifications, possibly resulting in fire or explosion.

Control: Use experienced operators and supervisors. Audit and apply proper QA/QC to assure that the unit is operated as designed. CONTROL POINT: Design, Operations

(6) Description: Since desorption treatment units operate electrical systems outdoors, workers may be exposed to electrocution hazards if the electrical equipment comes in contact with water.

Control: Verify that the hazardous area classifications, as defined in NFPA 70-500-1 through 500-10, are indicated on the drawings. All controls, wiring, and equipment, including adequate ground-fault protection, should be in conformance with the requirements of EM 385-1-1, Section 11.G and NFPA 70 for the identified hazard areas. CONTROL POINT: Design, Construction, Operations, Maintenance

(7) Description: All transfer equipment (conveyors, piping, process units and instruments) in contact with contaminated materials should be fabricated from materials that are chemically-resistant to that given chemical. Improperly designed systems can corrode or dissolve to a point of failure, and cause damage to the facilities or expose workers to collapse hazards from falling equipment.

Control: The materials of construction should be checked for chemical resistance. Typical chemical resistance charts can be found through the National Association of Corrosion Engineers (NACE). Where liquids may separate from solid materials, containment drip pans or receivers should be included in the design. Spill and/or leak detection instruments can be installed to monitor for leaks or spills and set off alarms when appropriate. CONTROL POINT: Design, Construction, Maintenance

(8) Description: The thermal desorption process may use high temperatures to heat materials. The materials that are processed will exit the system hot, exposing workers to possible thermal burns hazards.

Control: Safety control systems should be included to protect people and equipment. Signs should be posted warning of high temperatures. Safety barriers can be included to isolate critical sections of the equipment. The design of the systems should also consider the handling of these materials and follow NFPA criteria. Heat resistant gloves may be used to help prevent thermal burns. CONTROL POINT: Design, Operations, Maintenance

(9) Description: Transfer systems such as screw conveyors or augers expose workers to injury if limbs or clothing are caught in the system.

Control: Transfer systems should be enclosed to the maximum extent possible. Emergency shutoff controls should be installed in multiple locations. Lock-out/tag-out procedures should be rigorously enforced. CONTROL POINT: Design, Operations, Maintenance

(10) Description: Depending on soil types, exposure to respirable quartz may be a hazard. Consult geology staff to confirm the presence of a respirable quartz hazard (e.g. to determine if soil types are likely to be rich in respirable quartz. As an aid in determining respirable quartz exposure potential, sample and analyze site soils for fines content by ASTM D422, followed by analysis of the fines by X-Ray Diffraction to determine fine material quartz content.

Control: Worker exposure to dust rich in respirable quartz may be minimized by periodically wetting the soil with water or amended water or by the use of respiratory protection, such as a air-purifying respirator equipped with HEPA(N100, R100, P100) filters. CONTROL POINT: Construction, Operations

(11) Description: During site activities, workers may be exposed to direct and indirect sunlight and the corresponding ultraviolet (UV) radiation. Even short-term exposure to sunlight can cause burns and dermal damage. Exposure to hot and humid conditions may also result in heat stress, which can manifest itself as heat exhaustion and heat stroke.

Control: Exposure to direct and indirect sunlight should be minimized where possible in the summer months. Workers can minimize direct sun exposure by wearing long-sleeve shirts and full-length pants, and by applying UV barrier sunscreen. If possible, the work and break areas should be shaded. Exposure to heat stress conditions can be minimized by taking frequent breaks, drinking adequate fluids, and performing work during the early morning and late afternoon hours. CONTROL POINT: Construction, Operations

(12) Description: Workers may be exposed to electrocution hazards when working around electrical utilities such as overhead power lines.

Control: The location of overhead power lines, either existing or proposed, should be noted in the pre-design phase. All lifting equipment should remain at least 10 feet from the power line, according to Occupational Safety and Health Administration (OSHA) regulation 29 CFR 1926.550 and EM 1-1, Section 11.E. CONTROL POINT: Design, Construction, Operations

(13) Description: During the implementation of field activities, equipment and workers may come in close proximity to traffic. Also, equipment may need to travel or cross public roads. The general public may be exposed to traffic hazards and the potential for accidents.

Control: Where equipment is to cross over roads, warning signs should be used according to the criteria of the Department of Transportation Manual on Uniform Traffic Devices for Streets and Highways. A traffic management plan should be developed before remediation activities commence to help prevent accidents involving site trucks and automobiles. EM 385-1-1, Section 21.I.10 provides plan details. CONTROL POINT: Design, Construction, Operations

(14) Description: Workers may be exposed to infrared radiation hazards associated with working in the vicinity of thermal desorbing treatment units. The exposure, depending on the temperature of the equipment, length of exposure, and other variables, may increase the risk of cataracts.

Control: Workers should minimize their exposure to heated equipment surfaces. If prolonged work is required, eye protection using the appropriate shade safety glass may help to control exposure to the eyes. CONTROL POINT: Operations, Maintenance

(15) Description: Workers may be exposed to confined-space hazards during entry into the process equipment for repair, inspection, or maintenance activities. Confined-space hazards may include exposure via the inhalation route to toxic materials (e.g. vinyl chloride), and/or exposure to an oxygen-deficient atmosphere, or entanglement.

Control: Prior to entry into tanks, vessels or other confined space, testing of the atmosphere within the space may be required. Air handling systems should be designed to minimize or eliminate oxygen-deficient locations. Air-supplied respirators may be needed to help control inhalation exposures to toxic chemicals (e.g. vinyl chloride) or to help prevent asphyxiation. CONTROL POINT: Operations, Maintenance

b. Chemical Hazards

(1) Description: Worker exposure to waste materials may occur during excavation and transport of waste materials. Dry soils may generate airborne dusts contaminated with toxic materials (e.g. respirable silica, metals, semi-volatile organics, pesticides, etc.).

Control: Controls for preventing the generation of airborne dusts include periodic wetting of the dust and use of respiratory protective equipment (e.g. an air-purifying respirator with approved filter/cartridges [HEPA(N100, R100, P100) filters for particulates, OV cartridges for vapors, or combination filter/cartridges for dual protection]). CONTROL POINT: Operations

(2) Description: During operation of the desorption unit, workers may be exposed to byproducts of incomplete combustion such as carbon monoxide, or to airborne toxic materials, including metal acetates, mercury, and chlorine.

Control: Wastes should be classified prior to desorption, and only those waste materials compatible with the process should be fed into the unit. When such materials are known or suspected in the waste byproducts, the design of the process and off-gas treatment should control their generation and release. If control is not possible with the design, the personnel should operate with the appropriate PPE (e.g. an air-purifying respirator equipped with filters/cartridges appropriate for the contaminants of concern) and air emissions controls. CONTROL POINT: Design, Operations

(3) Description: During maintenance of the desorption unit, workers entering the unit for cleaning, inspection or repair of equipment may be exposed to waste materials or incomplete combustion byproducts (e.g. metal acetates, mercury, chlorine, etc.). In addition, workers may be exposed to toxic vapors or an oxygen-deficient atmosphere by entering into confined space.

Control: The hazards associated with exposure to these materials should be assessed at the time of entry, and the appropriate personal protective equipment worn. Confined-space entry procedures should be used, if appropriate. The facility and unit should be designed for ease of cleaning and maintenance to minimize the frequency, duration, and extent of exposure. CONTROL POINT: Design, Maintenance

(4) Description: Workers may be exposed via the inhalation exposure route during the thermal desorption process. Since some chemical contaminants, such as fuel oils, are not completely destroyed in the process, they may be discharged via the exhaust stack into the work area.

Control: Exhaust vapors must be gathered and further processed in an off-gas treatment unit, (e.g. vapor carbon beds, incinerators, thermal oxidizers or gas scrubbing towers). Fugitive emissions are possible if systems are not designed to address these issues. Systems that are operated in below atmospheric pressures will eliminate fugitive emissions problems. CONTROL POINT: Design, Operations

(5) Description: If the soil or materials being treated are rich in silica-based materials such as quartz, worker exposure to crystalline silica dust may occur. Soils composed of silt and clays are likely to create atmospheres with high respirable dust concentrations.

Control: Feed material and ash should be kept slightly moist to suppress dust. Perform adequate maintenance and seal all leaks in the thermal treatment system to reduce the generation of emitted silica or other dust. Geotechnical staff should be consulted to determine if site-specific soils are rich in quartz particles. At a minimum, air-purifying respirators with high-efficiency filters should be provided to workers. CONTROL POINT: Operations, Maintenance

c. Radiological Hazards



d. Biological Hazards




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