21-2 Hazard Analysis

Principal unique hazards associated with vapor-phase carbon adsorption include:

a. Physical Hazards

(1) Description: Fires may result when this treatment technology is used for treatment of some components in wastes. For example, hydrogen sulfide may cause carbon bed fires because of its high heat release upon adsorption, or peroxides may auto-ignite.

Control: Select an alternate technology during design if the known or anticipated contaminants pose an unmanageable threat of fire. CONTROL POINT: Design

(2) Description: Entering the carbon bed tanks for activities such as inspection, repair, and maintenance may constitute a confined-space entry. Hazards associated with entry into confined space include asphyxiation from the lack of oxygen, exposure to toxic wastes, microbial growth on the carbon, and engulfment/entrapment by the carbon bed.

Control: A confined-space entry program, including testing of the atmosphere inside the tanks, should be developed to help assess and control the hazards associated with confined-space entry. CONTROL POINT: Operations, Maintenance

(3) Description: During the transfer of flammable or combustible gases to the adsorption bed, a fire or explosion hazard may exist if the gas is ignited by equipment not approved for flammable locations, or from the discharge of static electricity. Fire can also occur during removal of carbon from the vessel.

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 on and near the beds should be in conformance with the requirements of EM 385-1-1, Section 11.G and NFPA 70 for the identified hazard areas. The transfer systems should be properly bonded and grounded to help prevent static discharge, if required by EM 385-1-1, Section 11.G or NFPA 70. Only trained, experienced workers should be permitted to work around the beds. CONTROL POINT: Design, Construction, Operations, Maintenance

(4) Description: Carbon holding tanks or drums containing carbon that has been saturated with VOCs may leak or spill over into the surrounding areas during operations or loading and unloading of carbon. The resulting spill may be ignited by a heat or spark source and catch fire. Conditions during which the carbon may be heated may increase this risk.

Control: Carbon holding tanks or drums should have adequate spill containment. Spill and/or leak detection instruments can be installed to monitor for leaks or spills and set off alarms when appropriate. 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 on and near the tanks or drums should be in conformance with the requirements of EM 385-1-1, Section 11.G and NFPA 70 for the identified hazard areas. All electrical systems should be properly marked for potential hazards, and only trained and experienced workers should be permitted to work in the areas. The area should also be adequately ventilated to help prevent the accumulation of VOCs. CONTROL POINT: Design, Construction, Operations, Maintenance

(5) Description: Vapor transfer systems equipment (pumps, fans, blowers, piping, pipe fittings, valves and instruments) in contact with contaminated vapors can corrode or dissolve to a point of failure and cause damage to the facilities or exposure to workers. The result may cause an explosion of a pipe or other vessel.

Control: Vapor transfer systems equipment (pumps, fan, blowers, piping, pipe fittings, valves and instruments) in contact with contaminated vapors should be fabricated from materials that are chemically-resistant to contaminants in the system. Hydraulic Institute standards HI 9.1-9.5 discuss appropriate materials for pumping various fluids. Typical chemical resistance charts can be found through the National Association of Corrosion Engineers (NACE). CONTROL POINT: Design, Construction, Maintenance

(6) Description: Carbon beds can be operated under pressure or vacuum. Systems designed to operate under pressure (e.g. fans, pumps, or blowers upstream from the carbon bed) have a potential risk of flammable vapor leakage which may explode or cause fire if ignited. Carbon dust can also be ignited and cause explosions. Reactions of chemicals, such as ketones, with activated carbon can be exothermic and cause fires or explosions.

Control: Where leaks may occur, 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. If the system requires a pressurized carbon bed, design tanks and piping for the maximum operating pressure expected. Over-pressure instrumentation should be installed to decrease the possibility of uncontrolled or fugitive vapor releases. These instruments can be set to shut down fans, blowers, or pumps. Over-pressure relief is usually required on these systems. The compatibility of the contaminants being absorbed and the carbon bed needs to be assessed to prevent exothermic reactions. Carbon should be handled to minimize the generation of dust or fines which might cause an explosion. The system design should minimize the potential for electrical spark or open flame, particularly during change out of carbon. CONTROL POINT: Design, Construction, Operations, Maintenance

(7) Description: Vapor-phase carbon systems operate better if the inlet vapors are at or below 50% relative humidity. Inlet heaters may be used. If the inlet vapors are overheated, spontaneous ignition of the carbon beds can occur.

Control: Temperature control instrumentation is required to monitor and control the operating temperature of the system. An alarm can be set off, and/or the input heat source and fans, blowers, or pumps can be shut down if the temperature out of a carbon bed exceeds 120EF [50EC]. CONTROL POINT: Design, Operations, Maintenance

(8) Description: Electrical systems can cause electrical shock to operating personnel.

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 should be in conformance with the requirements of EM 385-1-1, Section 11.G; NFPA 70; and CEGS 16415: Electrical Work, Interior for the identified hazard areas. Typical electrical hazard warning signs should be posted. CONTROL POINT: Design, Construction, Operations, Maintenance

(9) Description: Permanent or semi-permanent treatment buildings may present life safety hazards such as inadequate egress, fire suppression systems, and/or emergency lighting systems.

Control: Permanent and semi-permanent treatment system buildings should be constructed in accordance with ANSI 58-1: Minimum Design Loads for Buildings and Other Structures; the National Fire Code; the National Standard Plumbing Code; Life Safety Code; and the Uniform Building Code. Depending on where the project is located, the structures must also comply with either the Air Force Manuals on Air Force bases, the USACE Technical Manuals on Army installations, or Local Building Codes on Superfund, BRAC, or FUDS project sites. CONTROL POINT: Design, Operations

b. Chemical Hazards

(1) Description: If the vapor-phase carbon adsorber becomes saturated or is operated on hot days, VOCs may be adsorbed less efficiently by the carbon, causing an increase in VOC concentration in the exhaust. Workers in the area of the exhaust may be exposed to VOCs.

Control: Controls to help prevent exposure to VOCs include monitoring the discharge for VOCs and shutting down the system if the VOC inlet concentration exceeds a predetermined level. Respiratory protection (an air-purifying respirator with organic vapor cartridges) may also be used to control exposures. CONTROL POINT: Design, Operations, Maintenance

(2) Description: Workers may be exposed to VOCs via the inhalation exposure route when breakthrough of the activated carbon bed occurs. Breakthrough may result in high VOC concentrations in the exhaust.

Control: Periodically monitor effluent to determine when breakthrough occurs. Replace or regenerate carbon on a regular schedule. CONTROL POINT: Operations, Maintenance

(3) Description: Activated carbon can corrode carbon steel in tanks and piping, which may cause leaks and worker exposure to chemicals.

Control: Carbon steel should not be used to contain activated carbon. Stainless steel, thermoplastic, or other chemically-resistant tank materials should be used. Tank interiors may be painted, coated, or lined to prevent contact between activated carbon and carbon steel. CONTROL POINT: Design, Construction, Maintenance

(4) Description: During removal of saturated carbon, worker exposure to VOCs may occur.

Control: Monitor worker exposure to VOCs during carbon removal. Use respiratory protection appropriate for VOCs present (e.g. air-purifying respirator equipped with organic vapor cartridges) if worker exposure levels exceed permissible exposure levels (PELs). CONTROL POINT: Operations, Maintenance

c. Radiological Hazards

Description: NONAPPLICABLE

Control: NONAPPLICABLE

d. Biological Hazards

Description: NONAPPLICABLE

Control: NONAPPLICABLE