A new method to clean dust from soiled work clothes

D.E. Pollock, A.B. Cecala & J.A. Zimmer

National Institute for Occupational Safety and Health, Pittsburgh Research Laboratory, Pittsburgh, PA, USA

A.D. O’Brien

Unimin Corporation, Winchester, VA, USA

J.L. Howell

Unimin Corporation, Marston, NC, USA

ABSTRACT: Dust from worker’s clothes has been shown to be a problematic source of personal dust exposure.

A recently completed effort between NIOSH and the Unimin Corporation has resulted in a quick and effective

way to clean worker clothing. The process involves a booth under negative pressure with an air spray manifold

to supply compressed air to blow off the dust from the clothing. The overall system is designed to meet MSHA

and OSHA requirements. Results of field testing indicated that the manifold cleaned the clothes 10 times faster

and removed 50% more dust than cleaning methods used by workers today.

1 INTRODUCTION

New methods and techniques to lower respirable dust

exposures to workers in the mining industry are constantly being investigated by health and safety specialists. One area of known worker exposure throughout

all industries is from contaminated work clothing. For

the mining industry, a U.S. Bureau of Mines report

documented up to a 1 mg/m3 increase in worker’s dust

exposures on a number of separate occasions from

dusty work clothes (Cecala & Thimons, 1986). These

cases indicated that respirable dust levels were elevated to the extent that workers could be over their

exposure limit in less than two hours. As the individuals performed their work duties, dust was continuously

emitted from their clothing. The most effective way

to eliminate this dust source was to clean or change

their work clothing. In the past, the only MSHAapproved method to perform clothes cleaning was to

use a HEPA-filter vacuuming system which is very

difficult and time-consuming task to perform. Workers will sometimes use an air hose to blow off the

dust on their clothing. This method is prohibited by

both MSHA and OSHA and may cause exposure to

co-workers by liberating dust to the surrounding area.

A cooperative research effort between NIOSH and

the Unimin Corporation has resulted in an improved

method to clean the workers clothing.The new method

utilizes an enclosed booth which can either be ducted

to a baghouse dust collector, cleaned by a self

contained HEPA filter, or ducted outside. The booth

is under constant negative pressure therefore, no dust

liberated by the cleaning process contaminates the

surrounding area. A compressed air spray manifold

system was developed to remove the product from the

workers clothing. The system consists of a ball-valve

actuated steel pipe manifold with flat-fan air sprays

supplied by a 0.45 or 0.90 m3 (120 or 240-gallon)

air reservoir tank. The pressure to the system is regulated to 206.8 kPa (30 psi) to comply with MSHA and

OSHA regulations. The new method simply requires

the worker to don the required PPE, enter the booth,

actuate the air valve, slowly spin in front of the air

spray manifold (taking roughly 17 seconds), and exit

the booth with clean clothing.

On-site testing by NIOSH researchers has shown

that the new method is 10 times faster and removed

50% more dust than the currently used clothes cleaning

methods. It is both simple and cost effective and has

applications in the mining industry as well as other

industries where particulate contamination of clothing

is an issue. This new technique was recently approved

by MSHA under a petition for modification.

2CURRENT REGULATIONS AND

PROCEDURES

There are two federal regulations that affect the cleaning of clothes during the work day for the United
States mining industry. The first is a mining regulation established by the Mine Safety and Health

Administration (MSHA) in 30 CFR Part 56.13020,

which states: “At no time shall compressed air be

directed toward a person. When compressed air is

used, all necessary precautions shall be taken to protect persons from injury.” A second regulation is a

general industry standard established by the Occupational Safety and Health Administration (OSHA)

in 20 CFR 1910.242(b), stating that: “Compressed

air shall not be used for cleaning purposes except

where reduced to less than 206.8 kPa (30 psi) and then

only with effective chip guard and personal protective

equipment.”

Currently, the only approved method by MSHA to

perform clothes cleaning is to use a HEPA-filter vacuuming system. To perform this technique, a worker

uses the vacuum hose and manually moves the nozzle over his/her soiled clothing in an attempt to

remove the contamination. This is a very difficult

and time-consuming task to perform. Because of this,

some workers actually would prefer to use a single

compressed air hose to blow dust from their work

clothing, even though this is not an approved method

of cleaning. Using this technique can have numerous drawbacks to include: the use of higher than

OSHA approved pressures; and being performed in

the open work areas which not only contaminates the

worker, but co-workers as well. While investigating a

new approach to perform this clothes cleaning process,

it was critical to be able to meet the federal regulations

and standards and come up with a processthat workers

would want to use.

3 A NEW CLOTHES CLEANING PROCESS

The initial step of the clothes cleaning process design

was to develop a safe area to clean clothing. UNIMIN

Corporation purchased an enclosed booth and installed

it at their Marston facility, which provided the worker

sufficient space to effectively perform the cleaning

operation. Above the door was an open grate that provided an intake for the ventilation airflow. A return air

plenum located on the bottom-back wall of the booth

was ducted to the mill building baghouse dust collector

system, which provided a constant flow of air through

the enclosure. See figure 1.

Figure 1. Cleaning booth showing airflow.

The exhaust flow rate was measured at 2.17 m3/sec

(4,600 cfm).The booth had a negative differential pressure of 37.3 Pa (−0.15 inches w.g.). Since the booth

is under constant negative pressure, it proved to be an

effective area for clothes cleaning because it did not

allow any dust leakage into the plant.

The next critical aspect was to develop an effective

method to remove the product from the clothing. To

do this, air nozzles were installed in a spray manifold

that used compressed air to remove the dust from

workers’ clothes. Considerable design effort went into

determining the most effective spray nozzle manifold configuration and numerouslaboratory tests were

conducted at the NIOSH Pittsburgh Research Laboratory. Researchers also evaluated the impact of varying cleaning distances, clothing type, nozzle types,

nozzle spacing, air pressure, and spraying duration to

optimize the cleaning effect.

The airspraymanifoldwasfabricated from63.5 mm

(1– 1/2 inch) schedule 40 steel pipe that was capped at

the base. The air spray manifold was actuated by the

worker performing the cleaning process by operating

a timer-set pneumatic valve located on the top of the

manifold. The pneumatic valve had a safety interlock

option which would automatically shut the air supply to the manifold if the exhaust ventilation system

failed to keep the booth undersufficient negative pressure.Twenty-six (26)flatfan air nozzles were mounted

along the manifold, spaced on 50.8 mm (2-inch) centers. With this spacing, the flat fan nozzles seemed to

provide the most uniform cleaning.The bottom nozzle

was a circular design located 152.4 mm(6 inches)from

the floor. This nozzle was used in coordination with

a ball-type adjustable fitting that was directed downwards to clean the individual’s work shoes or boots.

See figure 2.

At a pressure of 206.8 kPa (30 psi), the air spray

manifold system expels 4.7 m3 (166 cubic feet) of air

for the typical cleaning period. In order to supply this

compressed air volume to the air nozzles for effective cleaning, a 0.45 m3 (120-gallon) air reservoir tank

was necessary. This tank was installed at the operation and was typically pressurized to the 1,034.2 kPa
(150 psi) level. The air reservoir was located directly

behind the cleaning booth and hard-piped to the air

spray manifold located inside the booth. Supply air to

the manifold wasregulated down to 206.8 kPa (30 psi).

The air regulator was located in a lock-box enclosure

to prohibit anyone from tampering with the air pressure.

Figure 2. Air nozzle manifold design.

Figure 3 shows the cleaning booth, air reservoir,

and air manifold configuration.

Figure 3. Booth, manifold and reservoir.

The worker performing the cleaning process is

required to wear a half-mask fit-tested respirator

with an N100 filter, hearing protection, and full-seal

goggles.

4EVALUATION OF THE THREE CLEANING

METHODS

Field evaluation consisted of randomly testing the

three different cleaning methods. The HEPA vacuuming system, the single air nozzle regulated to 206.8 kPa

(30 psi), and the air nozzle manifold system which

was also regulated to 206.8 kPa (30 psi). All of these

methods were performed in the booth.

Two gravimetric dust sampling racks were constructed to sample inside and outside of the booth.

Each rack consisted of two pumps (calibrated to 1.7

liters/min), two 10-mm Dorr-Oliver cyclones and two

37-mm pre-weighed dustfilter cassettes. One rack was

hung on the inside of the booth adjacent to the spray

manifold.The otherrack was hung outside ofthe booth

near the door. The weight gains on the two filters at

each location were averaged to provide an average

respirable dust mass for each location.

The instantaneous monitor used during this testing

was the Personal Data RAM (pDR) by Thermo Electron Corporation which was set to active sampling

mode. One pDR sampler was hung on the outside

booth rack and one on the inside booth rack to enable a

real-time dust concentration track inside the booth and

monitor for outside contamination during the testing.

In order to test for possible contamination of the

worker by leakage around the 1/2-mask respirator,

researchers utilized a barbed fitting which is commonly used during fit testing ofrespirators.Thisfitting

was installed between the 1/2-mask respirator and one

of the filter cartridges. A piece of flexible tubing connected to 1/2-mask respirator to an air-tight box which

housed a 10-mm Dorr-Oliver cyclone. This cyclone

was connected to another pDRin activemode.Thissetup enabled real-time monitoring for contamination in

the respirator during testing of the cleaning methods.

A matrix of tests was performed at UNIMIN’s

Marston plant to evaluate the effectiveness of this

newly developed technique. For this field testing,

the new clothes cleaning technique was compared to

the vacuuming system and the single handheld compressed air nozzle. In addition, two different coverall

types were tested, with one being 100 pct cotton and

the other a cotton-polyester blend. Prior to each test,

the coveralls were soiled with inert limestone dust to

a degree that represented an extreme case of soiling.

The weighing procedure consisted of pre-weighing

the clean coveralls and placing them in a pre-weighed

bag. Once the coveralls were soiled, they were placed

in the bag and weighed again. The researcher then

removed the coveralls from the bag (which was postweighed) and put on the coveralls while standing on a

pre-weighed piece of brattice cloth. The brattice piece

was then weighed to account for any dust lost while

donning the coveralls. After the test method was performed, the coveralls were removed while standing on
a pre-weighed piece of brattice and placed in a preweighed bag. The coveralls and bag were weighed

together and the brattice was weighed to account for

any dust lost while removing the coveralls.This extensive weighing regimen was developed to account for

all dust lost during each test.

Each test was timed by a stopwatch to determine

the actual cleaning time. Results of testing indicated

that the manifold cleaned the clothes 10 times faster

and removed 50% more dust than the single air nozzle

or vacuuming methods. Table 1 provides the average

cleaning times and the remaining dust weights on the

coverallsfromthe three different techniques evaluated.

Table 1. Amount of dust remaining on coveralls after

cleaning time for cotton and polyester/cotton blend coveralls.

Poly/Cot Poly/

Cotton Cotton Blend Cot Blend

Dust on Clean Dust on Clean

Cleaning Coveralls Time Coveralls Time

Method (grams) (sec.) (grams) (sec.)

Vacuuming 63.1 398 45.5 346

Air Hose 68.8 183 48.4 173

Manifold 42.3 17 21.9 18

These values represent averages calculated for two

NIOSH test personnel and a total of 96 tests. Figure 4

shows the relative effectiveness of the cleaning techniques tested.

Figure 4. Effectiveness of cleaning methods.

Respirable dust samples taken inside the respirator

of the test personnel performing the clothes cleaning

process showed minimal to no respirable dust exposure. In more than half of the 48 tests performed

with the airspray manifold, the testsubject’srespirable

dust concentration remained at 0.00 mg/m3 inside the

half-mask respirator. See figure 5.

Multiple test dust concentration 

Outside booth Inside booth Inside respirator 

100.0

90.0

80.0

Dust concentration, mg/m3

70.0

60.0

50.0

40.0

30.0

20.0

10.0

0.0

08:54:50 08:57:45 09:00:40 09:03:35

Time, hr:min:sec 

Figure 5. pDR results showing dust concentrations during

tests.

In the remainder of the tests, the value remained

very low with an overall average respirable dust concentration of 0.02 mg/m3 for the entire test group.

Figure 6 showsthe effectiveness ofthe booth to remove

the dust which is liberated from the spray manifold. Dust concentration, mg/m3

100.0

90.0

80.0

70.0

60.0

50.0

40.0

30.0

20.0

10.0

0.0

Time, hr:min:sec 

Single test dust concentration 

Outside booth Inside booth Inside respirator 

08:54:50 08:55:05 08:55:20 08:55:35 08:55:50

Figure 6. pDR results showing a single test.

Note that there was no contamination to the outside environment during the testing. Figure 6 also

shows the short time-frame to bring the inside booth

concentration back to zero.

Another factor evaluated during this study was the

cleaning effectiveness of the process on two different

coverall fabrics. As Table 1 shows, there was a significant improvement with the cleaning effectiveness of

the polyester/cotton blend coveralls when compared

to the pure cotton type. This needs to be considered

by operations implementing this new clothes cleaning

process.

With the air spray manifold design, the flat fan nozzles extend 79.4 mm (3-1/8 inches) from the supply

pipe and could easily be broken off ifstruck forcefully.

Because of this, it is recommended that side barriers
be installed to protect the air nozzles. During field testing, 25.4 mm (1-inch) wood sheeting was used along

both sides of the nozzles, providing an effective barrier

to minimize the potential for nozzle damage.

The air spray manifold was designed for a person

177.8 cm (51

–1011) in height, which was chosen based

upon the 50-percentile height for a male worker.Taller

workers will have to stoop and drop their shoulders to

effectively clean their upper body. When a person is

shorter, the top air nozzles can be covered with deflectors to prevent the air sprays from directly hitting the

individual’s face. During the final field test, the top

four nozzles were modified with deflectors attached

to the side barriers fabricated from 101.6 mm (4-inch)

PVC pipe that was cut in half and then into 50.8 mm

(2-inch) wide strips. Latches were attached on both

sides of these deflectors so they could be locked in

either the open or closed position.

A primary concern regarding any type of new technology is the cost of implementation. The total cost

of the clothes cleaning unit should be in the $3,000

to $4,000 range, excluding the cost for the exhaust

volume of air and ductwork cost. The clothes cleaning process utilizes compressed air as the cleaning

medium. The compressed air utility available at the

operation must be analyzed to ensure that critical processes are not starved due to the operation of the

clothes cleaning process. A dedicated compressor to

supply the necessary air may be an option in this case.

At the UNIMIN Marston Operation test site, an

excess exhaust volume was available in the baghouse

and thus was used forthissystem. Most operations will

not have this luxury and this will have to be built into

the cost. UNIMIN and NIOSH are in the process of

testing a cleaning system for operations without available baghouse capacity which will utilize an exhaust

fan to blow the dust-laden air up a stack to the outside

of the facility. Since the amount of dust removed from

a worker’s clothing will be relatively minor in relation to the amount of air necessary to place the booth

under negative pressure, the respirable dust concentration of air coming out ofthisstackmost likely would be

insignificant. Testing of this system will be performed

at the UNIMIN Elco Operation located in Elco, IL, in

the near future.

5 CONCLUSIONS

The new clothes cleaning process proved to be very

efficient since the worker only needed to don the

required PPE, enter the booth, actuate the automatic

valve, slowly spin in front of the air spray manifold

(taking roughly 17 seconds), and exit the booth with

clean clothing. This process has been demonstrated

to be a much more effective method to remove dust

from a worker’s clothing than methods currently used

by workers. Although this process was designed for

workers in the mining industry, it is applicable to

any industry where contaminated work clothes are a

problem.

It must be noted that this newly designed clothes

cleaning technique is not currently blanket approved

by MSHA for U.S. mining operations. A Petition of

Modification has been granted to UNIMIN Corporation by MSHA for use of the clothes cleaning process

at the Marston plant. Operations wanting to use this

technique may receive MSHA approval on a case by

case basis.

REFERENCE

Cecala, A.B. & Thimons, E.D. 1986. Impact of Background

Sources on Dust Exposure of Bag Machine Operator. US

Bureau of Mines Information Circular. IC 9089.