Minding your own business

The asphalt paving industry initiates testings and new controls to increase worker comfort and alleviate exposure to fumes

Asphalt Article December 28, 2000
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No one likes busy-bodies butting into their business. It is especially annoying
when the meddler lacks the knowledge that comes with years of experience.


Perhaps the largest and most extensive busy-body in America is the federal
government. At times there seems to be a regulation covering every aspect
of our lives and businesses. Despite some people questioning the wisdom
of all these rules and regulations, they do fulfill the need for protecting
the safety and well-being of America's citizens.


However, others view these regulations as an interference. They advocate
a laissez-faire government in the belief that business and commerce would
be better off with little or no governmental regulations. Allowing business
to regulate itself seems like a simpler solution than governmental interference;
however, can the public rely on the altruism of business.


The asphalt-paving industry is one business that decided to alleviate a
potential problem before the federal government stepped in to regulate.
The issue is the exposure of paving crews to asphalt fumes. It has long
been accepted that the heat of the fumes increases the temperature behind
the paver, adding to the discomfort of the crew. The use of newer asphalt
mixes also is turning up the heat. As polymers are added to asphalt, the
mix becomes stiffer. To work with these mixes the temperature is increased
to 325 deg, resulting in even hotter temperatures behind the paver.


There also is some concern over whether or not the fumes pose a health hazard
to the crews. Leroy Mickelsen, chemical engineer for the National Institute
for Occupational Safety and Health (NIOSH) comments, "We can detect
minimal levels of asphalt fumes, but the levels are so low it is not known
whether there is a health concern or not." While NIOSH is not ready
to make a claim on the health effects, the National Asphalt Pavement Association
(NAPA) says exposure to asphalt paving fumes poses no serious health threat.


Early studies on asphalt fume exposure, conducted in 1991, provided no definitive
answers. Rather then wait, NAPA took a pro-active stance, and in May 1993
began working on a solution.


Robert M. Thompson, president of Thompson-McCully, a Michigan asphalt contractor,
had an idea. In a 1995 interview with ROADS & BRIDGES, Thompson said,
"If we eliminate the perceived problem and get the workers away from
the fumes, then there is no reason for concern" (see Public/Private
Partnership Studies Ways to Reduce Asphalt Fumes, May 1995).


As the chairman of NAPA's Engineering Controls Task Force, Thompson met,
in 1994, with Byron Lord, then division chief in the Federal Highway Administration's
(FHWA) Office of Research and Development. The FHWA helped secure funding
and the cooperation of NIOSH. With the collaboration of asphalt paving contractors,
equipment manufacturers and unions, NAPA, NIOSH and FHWA launched an engineering
control evaluation program to test Thompson's hypothesis.


It was decided that there would be two phases to the testing: a lab test
and a field test. Some of the paver manufacturers that agreed to participate
in the tests include: Cedarapids, Blaw-Knox, Roadtec, Champion (formerly
Ingersoll-Rand) and Barber-Green (now owned by Caterpillar).

NIOSH and the manufacturers have finished the lab portion of the tests-at
each participating manufacturers' facility- and the findings are in the
process of being compiled and written.


During the lab tests a tracer gas was used to simulate the release of fumes
from the asphalt paver. The gas was measured with a multi-gas sampler to
determine what percent was being diverted by the controls. On June 5-7,
1995 Roadtec cooperated with NIOSH in a series of lab tests. A smoke generator
was used to produce theatrical smoke between the tractor and the screed
around the augers. According to a NIOSH draft document, as reported in Industry
Update, Roadtec's newsletter, the average indoor&shyp;capture efficiency
was 100% with an exhaust volume near 2,600 cu ft.


The paver was then moved outside to be tested in different wind conditions.
When the paver was positioned facing north with the wind blowing from the
northwest at 5-10 mph, the average capture efficiency was 81%. Next, the
paver was moved to face west. With the wind still coming from the northwest
at 5-10 mph the efficiency remained at 81%. From these tests it was hypothesized
that the controls will result in a reduction in asphalt fumes. This hypothesis
was reached even though the wind reduced the efficiency of the controls
when used outside. It was reasoned that the wind was responsible for removing
the other 19% of the asphalt fumes.


Based on the lab results a preliminary field test was conducted in early
October 1995, in Maryland, near the Washington, D.C., metropolitan area.
The goal of this test was two-fold: to check the instruments' ability to
measure various parameters under actual conditions and to test the engineering
controls on the paver.


It was important to study the types of instruments that could be utilized
in the field because asphalt-fume exposure is very low and difficult to
measure. Leland Warren, design engineer for Blaw-Knox, explains, "The
concentration of the fumes' contents are right on the borderline of the
detection methods currently used." Tests had already been conducted
in the spring, on pavers without controls, in order to determine the instruments
to be used. From those tests it was decided to try particle or aerosol detectors
and an FID&shyp;organic&shyp;vapor detector.


NAPA and Roadtec's preliminary field tests used an RP180-10 paver. The tests
were conducted by running the paver with the controls on for a set period
of time and then turning them off to see how much the aerosol concentration,
in the air, changed at the rear of the paver. A total of six different areas
were tested around the paver. Nontoxic sulfur hexafluoride gas also was
released into the screed and auger area in order to measure how much gas
is vented out of the fans. This allowed the efficiency of the hood&shyp;collection
system to be tested.


Even after the preliminary tests, there was still some question as to what
detectors to use in the field tests. Mickelsen explains, "In the past
different methods were used to measure asphalt fumes, but there were mixed
results because of wind velocity and the varying rates of the fumes produced."
A perfect technique has not yet been devised, but NIOSH is working with
a chemist to develop a method to measure asphalt&shyp;fume exposure. Previous
methods only focused on separating individual components of the fumes. However,
Mickelsen says field tests should begin in the late spring or early summer
of this year. These tests will measure the fumes and temperature reduction
with the controls on the paver.


Paver manufacturers are beginning to offer controls on their products. Roadtec
is the first company to offer controls as a standard item on all its paver
models. Named the FXS fume extraction system it consists of two suction
fans that collect fumes from the auger and screed area and redirect them
away from the operator and wokers on the paver, dispersing them through
a single deck-mounted stack. Roadtec's Shuttle Buggy, a material- transfer
vehicle, also comes with the FXS system and uses two suction fans to divert
fumes from the conveyors and hopper section, exhausting them out through
a pair of stacks; one is located near the operator's station and the other
on the C-1 conveyor.


Caterpillar is another manufacturer participating in the tests. The company
has completed its lab tests and is waiting to perform the field tests pending
sched-uling. Cat has developed its own control designs; however, it is not
currently available as standard equipment on pavers. The company does plan
to custom offer the controls on new pavers.


Blaw-Knox's asphalt- fume controls vent the fumes away from the screed.
The fumes are then dispersed or incinerated through the engine air&shyp;
intake. The controls were exhibited at Blaw-Knox's booth at March's ConExpo&shyp;
Con/Agg; however, the device is not yet available on the company's pavers.
Pending finalization of the product, it should be ready in 60-90 days.


Cedarapids' engineers have designed and developed a fume-capture system
for use with its Grayhound paver line. The system uses hood&shyp;blower
units mounted over the left&shyp; and right&shyp;hand sections of the paver's
hot&shyp;mix&shyp;auger section. The blowers suck fumes through ductwork
into a muffler unit where asphalt fumes are combined with paver&shyp;engine
ex-hausts. The muffler then vents fumes and engine exhaust into the atmosphere. Like the other manufacturers, Cedarapids' system is still under-going tests with NIOSH; however, the company's fume&shyp;capture system is currently available as an option on its seven Grayhound paver models. Cedarapids plans to make the system standard on all paver units in the future.


The initiative shown by NAPA in working together with government agencies
and asphalt&shyp;industry members demonstrates its concern for the well-being
of asphalt workers and the industry's willingness to address concerns, once
they are identified, in lieu of regulations.

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