Chemical Database Solves Hanford Puzzle
More than 1,100 of the 1,800 identified chemicals did not have an OEL established by OSHA or ACGIH.
- By Mike Berriochoa
- Sep 01, 2006
CHEMICALS and the potential risk of exposure to their vapors go hand in hand, making worker protection a complex challenge for many firms. For CH2M HILL, a prime contractor on the U.S. Department of Energy's Hanford Site in Washington State, the complexity of this challenge is compounded by large volumes of radioactive waste intermixed with the chemicals.
The 53 million gallons of radioactive and chemical waste stored on the Hanford Site is the byproduct of decades of producing plutonium for the nation's defense. Plutonium production was halted in the 1980s, but the waste remains, and the company is responsible for safely managing this waste in 177 underground tanks until the waste can be treated and disposed.
The tanks, ranging in size from 55,000 gallons to 1.1 million gallons, are divided into 18 so-called "farms" and are identified according to which of five processing facilities generated the waste. Vapors from these underground tanks come up through pipes connecting the tanks to the surface. Vapors pass through high efficiency particulate air filters into workers' breathing space and often have an ammonia odor. However, there was uncertainty about other chemicals that could potentially be in the work space.
Two years ago, the contractor launched an initiative to better understand these vapors to help ensure worker protection from potential hazards. But until the data could be collected on which to base decisions, the company mandated that all workers would use supplied air when working inside tank farms. The company then instituted several first-of-a-kind initiatives that included development of an Industrial Hygiene Technical Basis document unique to the DOE complex. This document became the foundation for a comprehensive industrial hygiene protection program and set out a series of actions designed to improve workers' health and safety. The document identifies all of the known or suspected chemicals inside the tanks. It evaluates which chemicals produce vapors that could put workers at risk and how those vapors are released.
"The technical basis provides a methodology to determine if there are any hazardous chemicals in the worker breathing space. We measured all chemicals that could possibly be in the tank vapor space and then narrowed down the list of chemicals to be measured in the work space. We then had to define the level at which many chemicals could be hazardous, because no regulatory limit existed for those chemicals," said Susan Eberlein, CH2M HILL vice president for Science and Technology. Such an effort had never been done before in the DOE complex and was developed in just 18 months.
Tank Ventilation Systems
Hanford's underground tanks are buried under 10 feet of soil and grouped into the 18 farms. Each tank received waste from nearby processing plants, many of which date back 60 years to the beginning of the Manhattan Project that helped bring an end to World War II.
Many of the tanks have passive ventilation. Vapors pass through HEPA breather filters, but some escaped through worn flange gaskets or instrument cabinets. Other tanks have active exhausters attached to ensure a constant air flow. The passively ventilated tanks "breathe" with changes in atmospheric pressure, temperature differences between the inside of the tank and the surrounding atmosphere, and wind speed. Workers often report smelling odors that have been compared to ammonia or even to dirty socks.
Some of the actions taken during the past two years to resolve these fugitive emissions include sealing the sources, repairing equipment, and extending the height of breather filter stacks on selected tanks to move vapors up and away from workers' breathing space. As an added precaution, the company then required all workers to be on supplied air while working inside the tank farms until the vapors could be sampled and analyzed.
Ammonia has a very low odor threshold and can be smelled well before the concentration reaches an industrial hygiene limit. However, employees raised questions about the potential health effects of tank vapors, speculating that while they could smell ammonia, there could be other compounds coming from the tanks they would not be able to smell.
Creating the Data Foundation
In March 2002, CH2M HILL formed the Chemical Vapor Solutions Team to give workers a strong voice in resolving vapor issues. The team includes craft workers, professional staff, and managers. The company wanted those who best understood the concerns to be the ones to work on solving the problem. The company then developed its unprecedented Industrial Hygiene Technical Basis to identify and document the chemicals that were present or could be present in the tanks and to recommend a path forward.
The purpose for developing the basis was to establish a solid data foundation that would provide the company and its workforce a better understanding of chemical vapor behavior to ensure workers are not exposed to any chemical vapor at greater than 50 percent of the occupational exposure limit (OEL). OELs represent the level of a specific chemical to which an average person can be exposed, without harm. For instance, an eight-hour time-weighted average OEL indicates the level at which a person can work for eight hours, every work day, without harm. OELs are formally established by several regulatory and independent agencies for many chemical compounds and mixtures.
Consistent with industrial hygiene processes, the company compares measured levels of chemicals to established OELs to determine the appropriate level of protection necessary for its workers, in each work location and work activity. Jim Honeyman, director of Tank Farm Technical Integration, was given the difficult task of developing the technical basis. A chemical engineer with more than 30 years' experience at Hanford, Honeyman was well aware of the challenge ahead of him.
"The mission was to develop an unbiased, open-ended evaluation of the potential problems using a world-class approach that would account for all the technical facets of this intricate issue," Honeyman said. "We needed to completely understand which vapors are and aren't being released, and which are hazardous to our workers. We had to develop new sampling and analysis methods to measure key compounds. Those activities ultimately allow us to define what controls and personal protective equipment are necessary for each job in the tank farms."
Because this "living" document is the first-of-its-kind for this complex environment, CH2M HILL knew it would need additional expertise beyond its own staff that was independent to the company. So it brought in a team of outside, world-renowned experts in toxicology and industrial hygiene to help build the technical basis strategy and to ensure its findings would stand up to rigorous review. These experts made up the Independent Toxicology Panel. "We saw this team of outside experts as an essential component to help us maintain our objectivity and credibility," Honeyman said.
The first order of business was to compile an accurate inventory of tank chemicals and vapors. This was extremely complicated, given that waste stored in the tanks came from five different chemical processes and much of the waste had been intermixed over the years. While extensive characterization of the liquid and solids contained in the tanks was available, understanding of which chemicals would produce vapors and the resulting vapors present in the tanks had a number of data gaps. Honeyman's team made an extensive effort to identify every chemical that was known to be present or potentially present in the tank vapor space. Only then could they start the process of identifying chemicals of potential concern and determine whether there were appropriate methods available to sample and analyze for them. The Independent Toxicology Panel "helped us build the right logic in a very demanding time frame for every chemical that might possibly be present," Honeyman said.
The technical basis not only defined all identified or postulated chemicals in the tank headspace, but also reviewed available toxicity data for the chemicals. One of its most noteworthy features was the way chemicals were prioritized, for the purposes of control and monitoring, in looking at potential exposure levels and chemical toxicity.
"Waste tank vapor chemistry is a complex mixture of many different chemicals, often at low concentrations," Honeyman noted. During this effort, the company used additional experts to account for organic and inorganic chemistry, gas release and transport (ventilation and dispersion), where the vapors go once released (atmospheric physics), and what the potential harmful effect of the specific chemical could be on the body (toxicology). "In general, the potential for harm is a question of dose [exposure over time]," Honeyman said.
More IH Staff, Better Equipment Arrive
Honeyman and his team identified more than 1,800 chemicals and mixtures that could possibly be present in tank vapors, then narrowed the list down to approximately 60 that were classified as Chemicals of Potential Concern. A Chemical of Potential Concern is defined as any chemical found in at least one tank at more than 10 percent of its individual OEL.
But the issue of OELs presented another vital challenge. While OELs existed for many of the chemicals known to be or having the potential to be in tank vapors, there were more than 1,100 chemicals that did not have an OEL established by OSHA or the American Conference of Governmental Industrial Hygienists, the two entities that provide the limits used by the Department of Energy to protect workers.
"We had to establish a defensible methodology to evaluate potential hazards posed by these chemicals. Working with our experts, we chose to take on the difficult task to develop a screening OEL value for all 1,100 compounds, evaluate the potential hazards, and then use established toxicological methods for estimating an acceptable OEL unique to our workplace," Honeyman said.
For some of this work, Honeyman turned to experts in the petroleum industry. "Since many of the organic chemicals used in the nuclear fuel reprocessing plants were originally purchased directly from petroleum refineries, it was only logical that we turn to their experts for help," he explained. More than 700 of the tank waste chemicals were grouped by similarity to known petroleum products, allowing the adoption of standard petroleum industry mixture OELs.
In parallel with the development of the technical basis came the rapid growth and expansion of the company's industrial hygiene program. The technical basis document became the foundation necessary to develop the most effective industrial hygiene sampling plan to limit tank farm worker exposures to as low a level as feasible. As a result, more industrial hygiene staff were hired and trained. Additional industrial hygiene monitoring equipment was acquired and deployed in the field, new and updated procedures and training were implemented, and a new Exposure Assessment Strategy was released. "The upgrades were essential to add a needed measure of worker protection in the field," Director of Environmental Health Tom Anderson said.
Then came another challenge. Because many of the chemicals present in the tanks are not commonly found in other industries, new methods had to be developed to sample and analyze for these Chemicals of Potential Concern. "Developing these techniques was an arduous task but was a major step forward as we work to come up with the answers we need," said Anderson.
It was also essential to measure chemical vapors accurately in work areas. It was sometimes difficult because vapor emissions vary over time, complicating the ability to evaluate worst-case or even average air concentrations. With the deployment of improved monitoring instruments, however, the company now has the ability to reliably determine when vapors are being released from the passively ventilated tanks. That knowledge ensures data from the samples represent the highest concentrations of vapors in the workplace.
Sampling for the Chemicals of Potential Concern around the first group of tank farms in the sampling plan began in March 2005. Sampling then moved inside those farms, with samples taken directly on the breather filters and ventilation stacks, as well as at points varying distances away in each direction to document dispersion. Data from these samples are now being analyzed. Once the data are in hand, decisions can be made regarding engineering controls, administrative controls, and respiratory protection requirements necessary for safe worker entry into this part of the site.
So far, most of the sampling done in and around the tank farms has taken place when no waste is being disturbed. As retrieval activities move forward and waste is pumped from one tank to another, more sampling will be needed. The vapor hazard will be measured for each area and work activity, and appropriate controls will be selected.
In addition to the actions in the technical basis, the company recognized that employees needed to have a better understanding of tank chemistry. "Our workers are well trained and educated to safely handle radiation issues, but we had never offered them the same level of training when it came to tank chemistry," said Anderson. Working with its employees, the company created the first tank farm-specific Chemical Hazard Awareness Training class. The class provides workers with a basic understanding of chemical behavior and how the industrial hygiene technicians sample and monitor for chemicals in the workplace. This training is now required for all employees who have unescorted access into the tank farms.
How Respiratory Protection Changed
Sampling and analysis was initially focused on 35 of Hanford's tanks that are clustered into seven farms. Thousands of samples were taken in dozens of locations in and around the farms, yielding the data to support decisions regarding the appropriate levels of respiratory protection. Supplied-air respirators are no longer required for most work inside those particular farms, though vapor control zones are in place within 5 feet of each breather filter. Work inside these zones still requires the use of supplied-air respirators. For employees who are sensitive to vapor odors or who are not comfortable working without a respirator, supplied-air respirators are available on a voluntary basis.
"This has been a complex technical and worker safety challenge. There was no textbook explanation breaking down each step towards a solution, and this was not a one-dimensional problem," Honeyman said. There were numerous different angles to take into consideration, and CH2M HILL paved the way for others in the future by documenting its efforts.
Based on the success of the A-prefix sampling campaign and the lessons that were learned, similar sampling campaigns are under way in other tank farms where work activities are taking place.
This article appeared in the September 2006 issue of Occupational Health & Safety.
This article originally appeared in the September 2006 issue of Occupational Health & Safety.