MEMORANDUM

DATE: October 19, 2010

SUBJECT: Impacts of Prohibiting the Use of Conventional Spray Guns in the Wood Furniture Manufacturing Op erations Source Category

FROM: Kaye Whitfield, EPA/OAQPS/SPPD/NRCG

TO: Docket No.: EPA-HQ-OAR-2010-0786

The purpose of this memo is to document the impacts of eliminating the use of conventional spray guns by the Wood Furniture National Emi ssion Standards for Hazardous Air Pollutants (NESHAP).

When the rule was promulgated, conventional guns were used extensively. Since promulgation, the use of conventional guns in the wood furniture industry has diminished drastically, and they are now rarely used. Conventional spray guns have lower transfer efficiencies and higher emissions than other spray gun types. We believe that air assisted airle ss spray guns, which have higher transfer efficiencies, can be used in al l cases where conventional air spray guns were once
used.

Costs

The cost of no longer using conventional air spray guns is believed to be minimal. First, the expected life of a conventional spray gun is es timated to be one and one-half to two years 1 , at the longest. Therefore, conventional air spray guns in use today should reach the end of their useful life before the compliance date for the proposed revised standard.

Second, we anticipate no changes in coating formula tion will be needed to use air assisted airless (AA) spray guns rather than conventional spray guns. Therefore, there will be no cost change related to coating usage.

Third, the cost of an AA spray gun is estimated to be about $300 more than a conventional air

spray gun 2,3 , where the cost of a conventional air sp ray gun is about $200.00 on average, and thecost of an AA gun is about $500.00 on average. This is a small cost difference, compared with the potential coating savings by switc hing to a higher efficiency spray gun. We estimate that the cost savings of using less coating over the lif etime of the guns will exceed the $300 difference in price between the two types of guns.

Transfer efficiency is defined as the ratio of the mass of coating solids deposited on a surface to the total mass of coating sprayed, expressed as a percentage. Air assisted airless spray guns can
have transfer efficiencies as high as 65% and as low as 50%. 4,5 Conventional air spray guns can
have transfer efficiencies as high as 45% and as low as 35% 4,5

.
The following equations are taken from Reference 4 but the calculations are also supported by References 6, 7 and 8. 5,6,7,8 As shown in Equation 1, the transf er efficiency of a coating is proportional to the mass of coating solids that ar e deposited on the wood furniture part and is inversely proportional to the mass of co ating solids that is sprayed.

Equation 1
where:

TE = transfer efficiency (%) P = mass of coating solid s deposited (g solids) F = volume of coating sprayed (mL) d = density of coating (g/mL) S = weight percent solids of coating

The higher transfer efficiency of AA spray guns results in lower coat ing use, as transfer efficiency is proportional to the amount of co ating solids that are de posited on a wood furniture
component.

The amount of coating sprayed is inversely proportional to the tran sfer efficiency of the gun. To get one unit of solids on the part, a conven tional spray gun (using the maximum transfer efficiency of 45%) needs to use 2.22 gallons of co ating. To get one unit of solids on the part, an AA spray gun (using the minimum transfer efficien cy of 50%) needs to use only 2.0 gallons of coating. This increased transf er efficiency represents a 9.9 percent decrease in coating consumption.

For either type of gun, the annual costs are equal to the sum of th e cost of the spray gun and the cost of coatings. The cost of coatings is equa l to the product of the cost per volume of coating, the volume of coating used, and the number of days.These costs can be represented by Equations 2 and 3.

Equation 2

Equation 3

where:

C C = annual costs for conventional air spray gun $200 = cost of conventional air spray gun
V C = volume of coating used by conventional air spray gun (gal) P = price of coatings
C AA = annual costs for AA spray gun $500 = cost of AA spray gun
V AA = volume of coating used by AA spray gun (gal)

As shown in Equation 4, the costs of the two spray guns are equal when Equation 2 equals Equation 3.

Equation 4

As demonstrated above, there is a 9.9 percent d ecrease in coating usage when switching from a conventional air spray gun to an AA spray gun. This is demonstrated by Equation 5.

Equation 5

Using Equation 5, Equation 4 can be represented as Equation 6.

Equation 6

With further simplification, Equation 6 b ecomes Equation 7 and then Equation 8.

Equation 7

Equation 8

Assuming that the typical wood furniture facili ty operates 4 days per week and 50 weeks per year, the typical year contains 200 days. If th e typical cost of wood furniture coating is $25 per gallon, the $300 cost difference between the conventional spray gun and the AA spray gun will be recovered according to Equation 9.Equation 9

Complete cost recovery will occur when the AA spray gun is used at a rate of 1.36 gallons of coating per day for a year (at a co ating cost of $10 per gallon). If the cost of the coating is higher, the cost recovery will occur in less than a year.

Emissions

In addition to the reduction in costs, there would also be a reduc tion in HAP emissions by switching to an AA spray gun.

As shown in Equation 10, the volatile emissions from a coating per unit mass of coating solids deposited are proportional to th e volume of coating sprayed a nd inversely proportional to the mass of coating solids that are deposited on the wood furniture part.

Equation 10 where:

E = emissions of volatile coating components (g/g solids applied) VC = volatile content of the coating (g/L coating) C = volume of coating sprayed (L) P = mass of coating solids deposited (g)

The volume of coating sprayed in Equation 1 is the same as the volume of coating sprayed in Equation 10, except for the units. As shown in Equation 11, the volume of coating in liters in Equation 10 is 1,000 times smaller than the volum e of coating in milliliters in Equation 1.

Equation 11
where:

C = volume of coating sprayed (L) F = volume of coating sprayed (mL) 1,000 = conversion factor (1,000 mL/L)By combining Equations 1, 10, and 11, the amount of volatiles per unit mass coating solids applied that are emitted when a coating is sprayed can be shown as Equation 12.

Equation 12
where:

E = emissions (g volatiles/g solids applied) VC = volatile content of the co ating (g volatiles/L coating) C = volume of coating sprayed (L coating) 1,000 = conversion factor (mL coating/L coating) TE = transfer efficiency (%) d = density of coating (g coating/mL coating) S = weight percent solids of coating (%)

With further simplification, Equation 12 becomes Equation 13. Volatile emissions per unit mass coating solids applied from a sp rayed coating are inversely proporti onal to the transfer efficiency of the spray gun used to apply the coating.

Equation 13
where:

E = emissions (g volatiles/g solids applied) VC = volatile content of the co ating (g volatiles/L coating) d = density of coating (g coating/mL) S = weight percent solids of coating TE = transfer efficiency (%)Equation 14

Equation 15

Equation 16

The same coating is being used in both cases, so all the coating related variables cancel out, resulting in Equation 9.

Equation 17

Equation 18

where:

E conv = emissions from the conventiona l gun (g volatiles/g solids applied)
E AA = emissions from AA gun (g volatiles/g solids applied) VC = volatile content of the co ating (g volatiles/L coating) d = density of coating (g coating/mL) S = weight percent solids of coating
TE conv = transfer efficiency (%)
TE AA = transfer efficiency (%)

As shown by Equation 18, the emissions from the AA gun are 0.9 times the emissions from the conventional air spray gun. For every ten tons of HAP emissions from a conventional air spray gun, the AA gun only emits 9 tons.

Conclusion

Prohibiting the use of conventional air spray guns will result in cost savings and HAP reductions.

### References

1. Personal Conversation. Mr. Paul Masters. Owner, Spray Gun Repair Inc.,.Thompson, Connecticut. November 16, 2010.

2. Spray Gun World. http://www.spraygunworld.com/pr oducts/Asturo/2700/Index%202700Siphon.html

. Accessed September 27, 2010.

3. Spray Gun World. http://www.spraygunworld.com/Inf ormation2/AAA/CAT%20Gun%20Only.html

. Accessed September 27, 2010.

4. Spray Gun World. http://www.spraygunworld.com/Informati on2/Overspray/OversprayStart.html . Accessed October 24, 2010.

5. Pacific Northwest Pollution Prevention Research Center. Transfer Efficiency and VOC Emissions of Spray Gun and Coatin g Technologies in Wood Finishing . Seattle, WA: PPRC,

1992. http://www.p2pays.org/ref/01/00636.pdf Accessed August 10, 2010.

6. Environmental Technology Verification Coati ngs and Coating Equipment Program (ETV CCEP): ANEST IWATA Corporation LPH 400-LV HVLP Spray Gun – Testing and Quality Assurance Project Plan (TQAPP), September 2003, http://www.epa.gov/nrmrl/std/etv/pubs/06_vr_lph400.pdf

7. Environmental Technology Verification Coati ngs and Coating Equipment Program (ETV CCEP): HVLP Coating Equipment – Generic Testing and Quality Assurance Protocol, Revision 1, December 1999, http://www.epa.gov/etv/pdfs/vp/06_vp_hvlp.pdf

.

8. Environmental Technology Verification Coati ngs and Coating Equipment Program (ETV CCEP): High Transfer Efficiency Spray Equipment – Generic Verification Protocol, Revision 0, September 30, 2006, http://www.epa.gov/nrmrl/ std/etv/pubs/600etv07016.pdf

.Attachment 1. Price Quote for Conventional Spray Gun

From reference: http://www.spraygunworld.com/pr oducts/Asturo/2700/Index%202700Siphon.html

Model 77 Siphon Feed Spray Gun Conventional: Compare to Binks 2001 / 2100

Less parts - Superior Spray Pattern - Compact, light weight and balanced. Specially designed grip improves operator control and handling comfort. Max working pressure 90psi

SUPER SALE: Free Shipping (continena l US) No 2nd day air (call): $158.00

Select Size s-8188^op2^270 0

Amazing Features:

Setups

65 SS (1.5mm)

66 SS (2.0mm)

Pressure Series for Industrial Mate rials - Glues Indutrial Coatings. Stainless Steel Tips and Needles Siphon Pot IncludedAttachment 2. Price Quote for Air Assisted Airless Spray GunsFrom reference:http://www.spraygunworld.com/Information2/AAA/CAT%20Gun%20Only.htmlAAA GUNS ONLY BELOWBOBCAT/ COUGAR / AUTOMATICSStandard SetupWaterbase SetupSolvent Base / You Can Do WaterOr can be upgraded Waterbase H20 HereWater Base & Solvent Base - Yes!Bobcat Compact HandleGunYour Cost:ON SPECIAL!Free Shipping $468.00Tip Set Size - Recommendedshown - More below (call)Select Size(All Variable fans goes down uptoapprox 3" i.e. a 10" can go from7" to 10")s-8188^op2^GunH2O Bobcat Compact Handle GunYour Cost:ON SPECIAL!Free Shipping $488.00*extra tips on special with purchase of GunTip Set Size - Recommended shown - Morebelow (call)Select Size(All Variable fans goes down upto approx 3" i.e.a 10" can go from 7" to 10")s-8188^op2^Gun

### Attachment 3. Transfer Efficiencies of Conventional and Air Assisted Airless Spray Guns

From the following reference: http://www.spraygunworld.com/Informati on2/Overspray/OversprayStart.html