Stephen M. Bowes

Retrospective Benzene and Total Hydrocarbon Exposure Assessment for a Petroleum Marketing and Distribution Worker Epidemiology Study

A quantitative exposure-estimating algorithm for benzene and total hydrocarbons was developed for a case control study of petroleum marketing and distribution workers. The algorithm used a multiplicative model to adjust recently measured quantitative exposure data to past scenarios for which representative exposure measurement data did not exist. This was accomplished through the development of exposure modifiers to account for differences in the workplace, the materials handled, the environmental conditions, and the tasks performed. Values for exposure modifiers were obtained empirically and through physical/chemical relationships. Dates for changes that altered exposure potential were obtained from archive records, retired employee interviews, and from current operations personnel. Exposure modifiers were used multiplicatively, adjusting available measured data to represent the relevant exposure scenario and time period. Changes in exposure modifiers translated to step changes in exposure estimates. Though limited by availability of data, a validation exercise suggested that the algorithm provided accurate exposure estimates for benzene (compared with measured data in industrial hygiene survey reports); the estimates generally differed by an average of less than 20% from the measured values. This approach is proposed to quantify exposures retrospectively where there are sufficient data to develop reliable current era estimates and where a historical accounting of key exposure modifiers can be developed, but where there are insufficient historic exposure measurements to directly assess historic exposures.

Deposition of Inhaled Particles in the Oral Airway During Oronasal Breathing

The deposition efficiency of inhaled particles in the oral airway was examined under experimental conditions that simulated natural oronasal breathing during moderate and heavy exercise in three human volunteers. Monodisperse, spherical, nonhygroscopic particles were generated by condensing di-2-ethylhexyl sebacate vapor onto nuclei of sodium fluorescein, a fluorescent tracer. The mass median aerodynamic diameter ranged between 3 and 16 μm. The aerosol was inhaled by mouth without a mouthpiece. After inhalation, the subject gargled to remove the deposited fluorescent tracer from the oral airway. On average, during simulated moderate exercise, 58% of the 10 μm diameter particles and 79% of the 15 μm particles deposited in the oral airway. During simulated heavy exercise, deposition efficiency in the oral airway was lower than during moderate work. The site of particle deposition as determined with a radioactive aerosol was influenced by how widely the mouth was opened, either naturally in heavy exercise, o...

The Head Dome: A Simplified Method for Human Exposures to Inhaled Air Pollutants

Acute controlled exposures of human subjects to air pollutants are customarily carried out with whole-body chambers, masks, or mouthpieces. The use of these methods may be limited by cost or technical considerations. To permit a study involving a highly unstable pollutant, artificial acid fog, administered to subjects during natural breathing, a head-only exposure chamber, called a head dome, was developed. It consists of a transparent cylinder with a neck seal which fits over the subjects head and rests lightly on his shoulders. The head dome does not constrain the upper airways or impede exercise on a bicycle ergometer. Ventilation can be monitored accurately and unobtrusively with a pneumotachograph at the exhaust port of the dome. A thermocouple may be used to monitor the onset and persistence of oronasal breathing. For short-term exposures to unstable or reactive pollutants lasting up to several hours, the head dome is an effective alternative to a whole-body chamber and probably superior to a face mask or mouthpiece.

Nose-only inhalation system using the fluidized-bed generation system for coexposures to carbon black and formaldehyde

AbstractThe purpose of this research was to develop a nose-only inhalation toxicology system for exposing animals to carbon black and formaldehyde—both individually and in combination. This study discusses the modifications necessary to use a fluidized-bed generator to generate carbon black in the concentration range of 0.5–20 mg/m3 with a mass median aerodynamic diameter of approximately 2.5 μm. The specific recommendations involve changing the size and placement of the delivery and overflow tubes as well as installing a motorized ball valve to automate delivery of premixed bed material and carbon black to the generator. The inhalation chamber was modified from a previously published design. By using a cyclone preclassifier to remove the nonrespirable fraction of the aerosol and a laminar flow element to reduce inlet vortic-ity, it was possible to obtain a uniform chamber concentration with less than ±25% overall variation. The formaldehyde generation system produced stable concentrations in the range of...

CONFINED SPACE VENTILATION: TRACER GAS ANALYSIS OF MIXING CHARACTERISTICS

Dilution ventilation is often used to control potential airborne health hazards, fire, or explosive conditions by mixing contaminated air with uncontaminated (e.g., outdoor) air. Dilution ventilation of confined spaces is used to displace oxygen-deficient, explosive, or toxic atmospheres prior to worker entry. Application of dilution ventilation requires the selection of an empirical mixing factor. This study sought an objective means of measuring mixing effectiveness for application to selected petrochemical industry vessels. The tracer gas sulfur hexafluoride (SF6) was metered into the air entering the vessel of interest, and the SF6 concentration was monitored at the vessel exhaust with an infrared analyzer modified to sample at 90 L/min for rapid response. The rate of SF6 concentration rise and decay was recorded using a datalogger. The mixing factor was calculated on the basis of measured ventilation rates, vessel dimensions, and SF6 rise and decay curves. Air in the vessels analyzed did not exhibit ...

Noise Exposure Reduction Aboard on Oceangoing Hopper Dredge

Reported industrial hygiene surveys aboard seagoing vessels are few, despite the presence of many potentially hazardous chemical and physical agents aboard ships. This investigation focused on crew noise exposure aboard an oceangoing hopper dredge. Noise exposure criteria were adopted based on the 24-hr equivalent continuous sound level (Leq(24)) because of the absence of standards for U.S. shipboard noise exposure. Personal noise dosimeters were used to measure the noise exposure of watchstanders, whose duties were predictable and repetitive. Watchstanders with high noise doses were asked to estimate their duration of exposure in specific areas of the vessel to enable calculation of noise dose per space. Noise sources within spaces associated with high noise dose were identified by sound pressure and surface vibration analysis in octave bands. Almost all accommodation spaces (cabins, recreation rooms, dining rooms, and hospital) were sufficiently quiet (sound pressure levels [SPLs] less than 65 dBA) to permit hearing threshold recovery. Machinery space SPLs ranged from 85 to 108 dBA, and engineering personnel noise exposure exceeded the selected criterion of Leq(24) = 80 dBA. Selective noise abatement and use of an enclosed operating station in the engine room were recommended to control engineering personnel noise exposure. This approach to noise exposure assessment and reduction should be applicable to other oceangoing ships where personnel may be exposed to noise 24 hr per day for weeks at a time.

Volatile hydrocarbon exposure during in situ burning of crude oil at sea

Personal exposure of response workers (and other personnel) to volatile hydrocarbons and benzene was monitored as part of the Newfoundland Offshore Burn Experiment (NOBE), a major oil spill combustion trial organized by Environment Canada and sponsored by over 25 governmental and private organizations from Canada and the United States. Benzene and total petroleum hydrocarbons were monitored using organic vapor monitors and charcoal tubes and analyzed by gas chromatography. Benzene and total petroleum hydrocarbon exposures were generally very low during experiments involving in situ burning (the controlled combustion of oil on water); over 95% of the determinations were below the analytical limit of detection, which was usually less than 0.1 ppm. In situ burning of unweathered crude oil at an accidental oil spill would probably be associated with higher exposure to benzene and other volatile hydrocarbons than at NOBE if the crude (1) had a higher natural benzene content than the Alberta Sweet Mixed Blend u...