Pulmonary Function in Workers Exposed to Diesel Exhausts: The Effect of Control Measures

ABSTRACT

To assess the protective effect of exhausts pipe filters or respirators on pulmonary function, 15 workers in a tunnel construction site, truck and loading machine drivers, rock workers, and others were studied. The total and respirable dust, combustible matter in respirable dust, carbon monoxide, nitrogen monoxide and nitrogen dioxide were measured for each subject during entire work shifts. The effect of the exposure on the lung function variables was measured by dynamic spirometry, carbon monoxide single breath technique, and nitrogen single breath wash-out.

The exhaust pipe filtering had a protective effect, directly discernible in the drivers on vital capacity and FEV, and for the whole group on FEV% and TL. The dust respirators had no effect, probably because of the difficulties in correctly using personal protection under the circumstances in the tunnel. In the absence of a true exposure assessment, control measures for diesel exhausts can be tested by medical effect studies. Catalytic particle filters of diesel exhausts are one method of rendering the emissions less irritant, although they will not remove irritant gases. An indicator of diesel exhaust exposure should include the particle fraction of the diesel exhausts, but a discrimination between different sources of organic dust must be possible.

MATERIALS AND METHODS

Study Group

Altogether, 15 workers participated in the two studies. All except one worker were smokers or ex-smokers. The median age was 39 years, and the median time of employment was 9 years. In study 1, the trucks were equipped with exhaust pipe filters. There were: five drivers, including one loading machine driver; six rock workers, including two workers sprinkling water on debris from blasting to bind the dust during the loading operation of the trucks; and two workers occupied with assembling of ventilation ducts in the tunnel. In study 2, 12 workers used personal respirators: six were “rock workers,” including two workers sprinkling water on debris from blasting; and six were “drivers” (five truck drivers and one loading machine driver).

Conditions and Equipment

The study was conducted at a tunnel construction site. The excavation was carried out in both directions at the same time, from a position in the middle between the two end points of the tunnel. Ventilation air was blown through a ventilation duct to both ends of the tunnel. The tunnel was 3 km long at the time of the study. The rock consisted of slate with some quartz. Drilling and blasting with Prillit (an ammonium nitrate explosive) were going on at one end of the tunnel, while loading of debris by means of a diesel-powered loading machine on to three t o four diesel engine trucks and transport out of the tunnel were carried out at the other end.

The trucks were Kockums KL-442B with Scania diesel DS 14 motors and Caterpillar 769 B, both with displacements (stroke volume) about 14 liters. The loading machine was a Caterpillar 980 C with a displacement of 14.6 liters and fitted with turbo. The vehicles and the loading machine were run on so-called light diesel oil, with a lower content of sulfur than “heavy” diesel oil.

The exhaust pipe filters were a ceramic type from Emissionsteknik AB, with a catalytic surface layer to decrease the ignition temperature of the arrested “soot” particles to about 400°C. According to the specification of the manufacturer, the particle emission will be decreased by 85% by use of the filter. No oxidation catalyst for gaseous components of the diesel exhaust was used in this investigation.

The respirators were three “air stream helmets” and nine half-face masks. The airstream helmets (Royal Amplivox Airstream A44, RS-060-00- 13PSI) were fitted with a coarse dust filter RS-060-22-00P and a fine dust filter RS-060-23-04P. The half-face masks were of type SR-62/80 with dust filter 210. Official leakage value was lower than 0.1%. None of the filters retains gaseous substances to any appreciable extent.

Exposure Measurements and Chemical Analyses


In the exhaust pipe filter test (study group 1),whole shift exposure assessments were carried out on Monday to Thursday. In the respirator test (study group 2), the exposure assessments were carried out during the first shift of the week, with or without respirators, after 2 days of no exposure. Dust, respirable dust, carbon monoxide, nitrogen monoxide, and nitrogen dioxide were measured using man-carried sampling equipment as described by 1. Combustible matter in respirable dust (CMRD) was measured by means of low temperature ashing in an oxygen plasma oven [Kranz and Ekstrom, 19791. Formaldehyde was concentrated from the sampled air by chemosorption and analyzed using high-performance liquid chromatography [1, but the 24 concentrations recorded were very low, 0.008/0.007 ppm (average/standard deviation) and the values were not used in the following analysis.

Pulmonary Function

Dynamic spirometry gave values for forced vital capacity (FVC, liters), forced volume in 1 sec (FEV1.0, liters), and FEV10 in percent of FVC (FEV%), as described by 1. The carbon monoxide-single breath technique gave values for transfer factor (TLco, mmol * min-1 * kPa-’) and was measured using a gas mixture made up of 0.3% carbon monoxide and 10% helium, 20% oxygen, with the remainder nitrogen. The effective breath holding time (on average, 10 sec) was taken as including two-thirds of the inspiratory time, the time of the dead-space washout, and half the time of sample collection.

The nitrogen-single breath wash-out provided values for vital capacity (VC, liters), closing volume (CV, liters), and CV in percent of VC (CV%). The criteria for a successful maneuver required that the difference between expiratory and inspiratory vital capacity did not exceed 10%. The curves were analyzed according to 1.

The equipment for determining the transfer factor, TLco, consisted of a dry rolling seal-spirometer (Volugraph 2000s with Diffusimat 2000, Mijnhardt) with a helium analyzer based on the thermoconductivity principle. Carbon monoxide was analyzed according to the infrared absorption principle. For the nitrogen-single breath, a “bag-in-box” system was used, with analysis of nitrogen by an air ionization meter (Ohio 720). Volume and nitrogen concentration changes were simultaneously recorded on an X-Y recorder (Bryans 20000). The equipment was checked every day with 1 and 3 liter precision syringes. The volumes were corrected to BTPS [1. At least 5 min were allowed to elapse between determinations of closing volume and transfer factor, respectively, to avoid influences of different gas mixtures.

In the exhaust pipe filter test, (study group 1) FVC, FEV1.0, FEV%, CV%, and TLco, were determined. Because of technical limitation in the measurement of TLco, only six subjects could be measured with the exhaust pipe filters applied. The lung function tests were carried out after a work shift at the end of a working week without any filters installed and after a work shift at the end of a week when exhaust pipe filters had been installed and used for 2 weeks. In the respirator test (study group 2), VC, CV%, and TLco, were determined. The respirators were used during the first work shift in the week. The lung function assessments were made after a work shift without any control measure and after a corresponding shift with respirators. 

RESULTS


There was a clear improvement in the air quality in the tunnel when exhaust pipe filters were employed. The concentrations of the measured air contaminants are presented in the Table I. In study group 1, the filtering of the emitted diesel exhausts reduced the CMRD concentration, especially in the breathing zone of the drivers. The concentration of carbon monoxide was slightly higher with filters, while nitrogen oxides was lower with filters. These differences are not considered to affect the results, because there is no correlation between mitigation of lung irritation and air contaminants after filtering.

The efficiency of the control measures on lung function was assessed by quotients of lung function variables, “filter/no filter,” noted F/NF in the Table 11. FVC and (almost significantly) FEV1.0, are improved among the drivers. FEV% and TLco, improved for the entire group. The respirators had no effect in any measured variable (see Discussion).
