Engineering Controls for Furniture Strippers to Meet the New OSHA PEL for Methylene

Chloride

Cheryl Fairfield Estill, Daniel S. Watkins,

Stanley A. Shulman, Robert W. Kurimo,

Ronald J. Kovein

National Institute for Occupational Safety and Health

Centers for Disease Control and Prevention

Methylene Chloride OSHA PEL

• PEL reduced to 25 ppm

• Action level of 12.5 ppm– exposure monitoring– medical management

• April 10, 2000 – effective date for furniture strippers

Study Goal

• To design engineering controls to reduce employee exposures to below the 25 ppm PEL

Furniture Stripping

• Methylene chloride, methanol, toluene

• One employee

• Alternates between two workstations– stripping, 40% of time– rinsing, 44% of time

Previous Ventilation Design• 1991 study at this facility

• Local exhaust ventilation – strip tank only– two slots, front and back

• Exhaust volume – 2900 cfm

• Employee exposure – 59 ppm

Four Preliminary Surveys

• Survey 1, Aug ‘97 - test existing system,

– unrestricted make-up air

• Survey 2, Mar ‘98 - test existing system,

– no make-up air

• Survey 3, Jun ‘98 - upgrade and clean stripping area ventilation

• Survey 4, Jul ‘98 - add rinsing area ventilation

Results of Preliminary Surveys

334

7339

63

0

50

100

150

200

250

300

350

400

1st 2nd 3rd 4th

Survey

Exp

osu

re (

pp

m)

EmployeeExposure (ppm)

Final Survey Ventilation Design• Changes to Stripping Tank

– 60° transition piece

– new fan

– larger ductwork

– eliminated elbows in ductwork

Ventilation Design

• Rinse Area– ½ HP axial fan

– Enclosure - 3 sides and a top

– swivel table

Ventilation Results

• Stripping Tank– exhaust volume 2700 cfm– slot velocity 2600 fpm

• Rinsing Area– exhaust volume 2100 cfm– face velocity 120 fpm

Methods

• Breathing zone samples - one employee• Area samples, stripping and rinsing area• Bulk solution samples• OSHA Method 80 (ORBO tubes)• Two sampling days• 10 - one hour samples

Methods

• Employee Training– Employee watched a one-hour video– Talked with employee about work practices

• Stripping Solution– Height of stripping

solution– Paraffin wax

Results• Stripping solution - 14 inches from top• Paraffin wax was added• Methylene chloride content was 50%

Preliminary Survey 4 Final Survey

Results - Final Survey

0

5

10

15

20

25

BreathingZone

StrippingArea

Rinsing Area

GM MethyleneChloride Conc (ppm)

• Two runs were eliminated.• Geometric mean - 8 ppm• Upper confidence limit - 13 ppm

Comparison of Results

334

7339

8

63

0

50

100

150

200

250

300

350

400

1st 2nd 3rd 4th Final

Survey

Exp

osu

re (

pp

m)

EmployeeExposure (ppm)

Factors Which Reduced Exposure to Below PEL

• Local ventilation

• Stripping solution height, paraffin wax

• Employee training

Local Ventilation

0500

100015002000250030003500400045005000

Exhaust Volume (cfm)

1st 3rd 4th Final

Survey

StrippingRinsingTotal

Note: No ventilation measurements were taken during Survey 2.

Stripping SolutionEmployee Training

• Solution in the tank must be kept high.

• Paraffin wax must be used in the solution

• Employees must be trained

Costs

0

1000

2000

3000

4000

5000

6000

7000

Dollars

Strip Rinse Make-Up

Material Labor

$4545 $4340

$6840

Operating costs of make-up air system - $1000/year

Limitations

• Methylene chloride concentration - 50%• Costs are high• Three factors

– Ventilation– Stripping Solution– Work Practices

• It may take many iterations to reduce exposures to the PEL

Conclusions

• Technically feasible to reduce exposures to below the OSHA PEL

• Use of this system can reduce exposures below the action level.– The 95% upper confidence level was 13 ppm,

slightly above the action level.