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ANALYSIS OF DUSTS COLLECTED DURING TRIMMING AND CUTTING OF 

SPRAY POLYURETHANE FOAM (SPF)

Mark W. Spence

Spence Consulting, LLC

1232 Holyrood St.

Midland, MI 48640

Project Sponsored by the Center for the Polyurethanes Industry, 

SPF Research Work Group

16 March 2010
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ABSTRACT

INTRODUCTION

The primary purpose of the study was to establish sampling and analytical techniques 

which would be appropriate and practical for further field evaluations of worker exposure 

during trimming and cutting of spray polyurethane foam (SPF). Because of this, this 

study employed a protocol under controlled laboratory conditions designed to simulate a

trimming situation. This study is also an initial evaluation of the potential exposure of 

workers to inhalable and respirable dust and polymeric methylene diphenyl diisocyanate 

(pMDI) during the post-application trimming and cutting of open cell and closed cell SPF

insulation in interior applications. A copy of the protocol for SPF application and 

trimming and sampling and analysis is included in Appendix A of this report.

 

This study was conducted on December 14-15, 2009. On each day, SPF insulation was 

applied to sections of timber drywall assemblies to simulate actual interior wall 

application. Extra spray was applied so that the resulting foam extended well past the 

studs to provide adequate foam for extended trimming and cutting times. The wall 

sections were set aside for 1-2 hours before being trimmed to ensure that the SPF was in 

the “cured” form most likely to produce particulate when cut or trimmed. Personal 

exposure sampling and source air sampling was conducted during trimming and cutting.

EXPERIMENTAL

Facilities

This study was conducted in the Machine Hall of the Huntsman Advanced Technical 

Center, 8600 Gosling Road, The Woodlands, Texas 77381. SPF was applied in a 

ventilated spray booth equipped with a water cascade which was located in the Machine 

Hall. Trimming and cutting of the SPF was conducted in an environmental chamber 

within the Machine Hall. The spray booth and environmental chamber were located 

approximately 40 feet from each other.

Foam Systems

 

Open-cell foam – a nominal 0.5 pounds per cubic foot (pcf), polyether polyol-based 

polyurethane foam system typical of those currently used in interior wall spray

applications was used. 

Closed-cell foam – a nominal 2.5 pcf, polyester / polyether polyol-based rigid 

polyurethane foam system typical of those currently used in interior and exterior wall and 

roof spray applications was used. 

SPF Application and Trimming
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SPF insulation of one foam type (i.e. closed cell or open cell) was applied to multiple 

wall sections of timber drywall assemblies over about a 20-minute period. The foams 

were applied using a Graco “Reactor H25” spray unit fitted with 50 feet of hose and 

using a Graco “fusion” spray gun.

NOTE: In normal field application, sufficient spray is applied to expand to 

approximately the plane formed by the face of the studs. Trimming and cutting is then 

conducted to clear the face of the studs and bring any extra foam below the plane of the 

stud faces. In this study, extra spray was applied so that the resulting foam extended well 

past the studs over the entire wall section to provide adequate foam for extended 

trimming and cutting times, as shown in Figures 1 and 2.

After spraying, the wall sections were leaned against the wall in the Machine Hall in the 

vicinity of the environmental chamber and allowed to cure for approximately 40 minutes 

before trimming was conducted.

SPF insulation in the wall sections were cut and trimmed flush with stud surfaces using 

each of the trimming techniques described below over a 60-80 minute period. The wall 

sections were used in the order in which they had been sprayed. Trimming was 

conducted in an environmental chamber (interior dimensions: 254 cm high, 284 cm wide, 

325 cm deep) located in the Machine Hall. The chamber doors were open, but there was 

no additional ventilation beyond the general ventilation in the Machine Hall, which was 6 

air changes per hour. Observations with a smoke tube in the environmental chamber 

showed only very slight air currents in random directions. Temperatures and humidity

inside the chamber during trimming and cutting were 71.6 – 73.0 F (22.0-22.8 C) and 

41-46 %, respectively.

The process of SPF wall section preparation, curing, and trimming was carried out four 

times to give duplicate trimming sessions with each foam type where all trimming took 

place 1-2 hours after the foam was applied to the wall sections. 

TRIMMING TOOLS

Foam Planer – pneumatically-operated, wire-brush Tough Mechanics planer (planer 

brush: 9 cm diameter, 60 cm long) (Fig. 3)

Sander – Bosh 1028VSR hand-held electric drill with Norton “Stick and Sand” sanding 

disk (5” (12.7 cm) diameter) with Norton 40 grit sanding disk (Fig. 4)

Hand Saw – 36” x 1” (91 cm x 2.5cm) blade; 8 teeth per inch (Fig. 5)

Hand Scraper #1 – Husky #482 526 “14-in-1” Paint Tool, 3” (7.6 cm) blade (Fig. 6)

Hand Scraper #2 – Groomex #63306 dog shedding blade (Fig. 7)

TRIMMING TECHNIQUE GROUPS
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Trimming tools were grouped into “high dust potential” and “low dust potential” 

categories for the foam type on which they might be used in actual SPF insulation 

application based on subjective understanding of the techniques. The resulting groupings 

are shown in Table I.
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Table I. SPF Insulation Trimming Technique Groups

Trimming Technique Dust Potential

Group

Open Cell 

SPF

Closed Cell 

SPF

Hand Saw low X n/a

Foam Planer high X X

Sander high n/a X

Hand Scraper (#1 & #2) low X X

Trimming was conducted in duplicate 15-20 minute sessions (one on each day of the 

study) for each of the two trimming groups (high dust potential, low dust potential) for 

each SPF type (open cell, closed cell), as indicated in Table I. 

Exposure Monitoring

During each trimming session, personal exposure monitoring on the worker doing the 

trimming was conducted for pMDI, inhalable particulates, and respirable particulates. In 

addition, inhalable particulate source sampling was conducted by holding the sampler 12-

24 inches from the trimming area.

Samples were collected using SKC Aircheck 52 personal air sampling pumps. The 

sampling media was attached to the sampling pumps, the sampling pumps were flow

calibrated using a Bios Dry-Cal DC-lite Model 717-01 calibrator, and the sampling media 

was located in the worker’s breathing zone or near the particulate source before each 

trimming session. Figure 8 shows the samplers in place as they were worn by the worker. 

Source samples were held in the close vicinity (i.e., within 30 cm) of the point of contact 

between the trimming tool and the foam. 

Immediately after each trimming session, the sampling devices were retrieved, flow 

checked, and the samples were prepared for analysis as described in the “Monitoring 

Techniques” section of this report. All sampling equipment and sample analysis was 

supplied by the Bayer Materials Science Environmental Analytical Laboratory

(BMSEAL) in Pittsburgh, PA, an AIHA-accredited laboratory.

Background samples were collected for pMDI, inhalable particulates, and respirable 

particulates before the start of trimming each day. The samples were collected for 

approximately 30 minutes in the center of the environmental chamber and were mounted 

on a tripod about 24” (60 cm) above the floor.

SAMPLING AND ANALYSIS TECHNIQUES

Polymeric MDI

To conduct sampling for pMDI, the outlet nozzle of a pre-loaded 13-mm cassette was 

attached to the flexible tubing from the sampling pump to be used. The flow rate through 
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the cassette was set to approximately 2 L/min as specified in the method and recorded to 

a precision of two decimal places.

Following sampling, the sample flow was again measured and recorded, and then the 

filter cassette was opened and the 13-mm glass fiber filter was transferred using tweezers 

to a 4-mL glass vial. Using a pipettor (Gilson Pipetman 0-5 mL adjustable), 2.0 mL of a 

90:10 solution of acetonitrile (Honeywell B&J high purity): dimethyl sulfoxide (Fisher 

lot 061838) was added to the vial. The vial was capped with a polyseal cap and shaken 

well. The cap was sealed with pressure tape and a numbered sample label applied to the 

vial. The vials were packed in a DOT-approved shipping container for return to 

BMSEAL for analysis.

Samples were analyzed for pMDI concentrations according to Bayer Material Science 

Environmental Analytical Laboratory (BMSEAL) Method 1.7.7. The method is based on 

OSHA method 42, in which air is drawn through a glass fiber filter which has been 

treated with 1,2-pyridyl piperazine (1,2-PP). Isocyanates react with the primary amine 

functional groups on the 1,2-PP to form a stable derivative which serves as a sensitive 

analyte in subsequent liquid chromatography / ultraviolet detection (LC/UV) analysis.

Polymeric MDI (pMDI) is a mixture composed of MDI monomers (45-55%) and a series 

of larger, multiple-phenyl-ring, multi-isocyanate homologues of MDI (45-55%). Because 

characterized standards are only available for MDI and the pMDI mixture, the BMSEAL 

method employs instrumental calibration for these two analytes. In the case of pMDI, the 

three-phenyl-ring triisocyanate homologue of MDI is used as the calibration peak for the 

entire mixture. Thus, pMDI values reported by this method include the MDI mass; to 

estimate the total mass of the multiple-phenyl-ring, multi-isocyanate MDI homologues in 

the sample, the MDI result may be subtracted from the pMDI result.

The method reporting limit was 0.1 g for MDI and 3 g for pMDI. The 1,2-PP coated 

13-mm glass fiber filters were prepared by the BMSEAL and pre-loaded into 

polypropylene cassettes.

Two quality assurance samples which had been spiked with known amounts of pMDI 

were prepared by the BSEAL laboratory and included with the sampling equipment sent 

to the field. These samples were prepared in the field as if they had been field samples, 

following the desorption procedure described above and returned to the laboratory for 

analysis. In addition, two of the sampling filters were desorbed without having air drawn 

through them to serve as field blanks.

Inhalable Particulate

Inhalable particulate samples were collected and analyzed according to NIOSH Method 

0500. The samplers used were IOM personal samplers, conductive plastic version (SKC 

Cat. # 225-70A; Fig. 9). These samplers were operated at the 2 L/min sampling flow rate 

specified in the instructions for the device. The sampler consists of a sample cassette, 
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which contains the 25-mm sample filter, and a housing, which connects to the sampling 

pump and into which the loaded sample cassette is placed (Fig 9). The sample cassettes 

were loaded with 25-mm PVC membrane filters (5 m pore size, SKC Cat. # 225-8-04) 

and pre-weighed as a unit by the analytical lab.

To conduct sampling, a loaded cassette was removed from its numbered transport clip, 

placed in the bottom of the IOM housing, and the housing top screwed in place. The 

housing was then connected to the tubing from the sampling pump to be used; the flow 

was set to approximately 2 L/min (using calibration adapter SKC Cat. # 391-01), and 

recorded to a precision of two decimal places.

Following sampling, the sample flow was again measured and recorded, and then the 

sample cassette was removed from the IOM housing and replaced in the transport clip. A 

numbered sample label was applied and the sample was placed in a zipper bag for 

analysis. All handling of IOM sample cassettes was done using powder-free nitrile 

laboratory gloves to avoid adding weight to the cassettes from fingerprints.

Analysis consisted of gravimetric determination of the mass captured by the sample 

cassette; the reporting limit was 200g.

Respirable Particulate

Respirable particulate samples were collected and analyzed following NIOSH Method 

600. Pre-weighed 37-mm PVC membrane filters (5 m pore size) in three-piece 

polystyrene cassettes (SKC cat. # 225-803) fitted with a GS-3 conductive plastic cyclone

pre-selector (SKC cat. # 225-100) were used as the samplers. Figure 10 shows a diagram 

of the assembled sampler. These samplers were operated at the 2.75 L/min flow rate

specified in the method.

To prepare sampling equipment, the top section of a 37-mm filter cassette assembly was 

removed and the GS-3 cyclone was press-fitted onto the middle section of the cassette. 

The flow rate through the filter cassette / cyclone assembly was then set to approximately

2.75 L/min (using calibration jar SKC Cat. # 225-111), and recorded to a precision of two 

decimal places. The calibrated filter cassette / cyclone assembly was mounted in a holder 

(SKC cat. # 225-1) to facilitate locating it in proper orientation in the worker’s breathing 

zone.

Following sampling, the sample flow was again measured and recorded, and then the GS3 cyclone was removed from the filter cassette inlet and the polystyrene cassette top was 

placed back on the cassette. A numbered sample label was applied and the sample was 

placed in a zipper bag for analysis. The cyclone was wiped with a lint-free wipe and any 

contents in the grit pot emptied to prepare it for reuse.

Analysis consisted of gravimetric determination of the mass captured by the sample filter. 

The reporting limit was 30 g. 
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Inorganic Particulate

Following gravimetric analysis, the membrane filters from both the inhalable and 

respirable particulate samples were placed in a pre-weighed crucible then the crucible 

with the filter in it was heated for two hours in a furnace at 765 C. Following this, the 

crucible was cooled and re-weighed. Any additional mass remaining in the crucible after 

heating was interpreted as “ash” (i.e., mass from inorganic particulate and therefore not 

attributable to SPF).

RESULTS & DISCUSSION

Observations

The subjective grouping of trimming techniques into “low dust potential” and “high dust 

potential” was supported by visual observations. The pneumatically-powered foam 

planer generated by far the most observable foam particulate, followed by the sander. 

None of the three hand techniques (saw, scraper #1, and scraper #2) generated noticeable 

airborne particulate; their use resulted primarily in relatively large pieces of foam which 

fell to the floor as they were generated.

When using the foam planer, the character of the particulate generated was quite different 

between closed cell and open cell foam. With open cell foam, planer use produced fluffy, 

snow-like particulate that adhered to surfaces, presumably as a result of static charge. In 

contrast to this, particulate produced by planer and sander use on closed cell foam 

produced a much finer, powdery particulate which also adhered to surfaces.

Measurements

The detailed results of the air sampling conducted during SPF insulation trimming are 

given in Table II. Table III summarizes the results for each trimming group. The 

analytical laboratory reports are included as Appendices B-1 to B-4 to this report.

pMDI

In all trimming groups with both foam types, MDI and pMDI were not detected in the 

personal and source samples. This was true even in the case of the samples taken during 

the high dust potential techniques, where foam dust was observed inside the sampler after 

sampling and was included with the filter in the desorbed sample. The detection limit for 

these short-term task samples was a factor of at least 20 below the OSHA PEL of 200 g/

m

3

(Ceiling) and a factor of at least 5 below the 8-hour time-weighted average 

occupational exposure limit (ACGIH TLV®for MDI = 51 g/ m

3

).
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The results of the pMDI quality assurance samples are reported in Table IV below. The 

samples were spiked with a solution containing 4.65 g pMDI which had specifications 

of 40-45% monomer (MDI). The results of the spikes showed 95-110% accountability

for the pMDI amount spiked, and MDI monomer results which were 37-41%. These 

results demonstrate that the method was functioning as validated and could be expected 

to detect any pMDI that was present above the detection limit.

INHALABLE PARTICULATE

 

The inhalable particulate results largely mirror the subjective observations reported 

above: the results are highest for the pre-identified high dust potential trimming 

techniques with both foam types. The results for these short-term task samples were a 

factor of about 30 above the occupational exposure limit concentration (OSHA PEL = 15 

mg/m38-hour TWA and the ACGIH recommendation for inhalable particulate, not 

otherwise specified = 10 mg/m

3

).

The inhalable particulate results for the low dust potential techniques gave results below 

the 8-hour time-weighted average occupational exposure limit concentration in the case 

of the open cell foam. However, the mean concentration for the low dust potential 

techniques with the closed cell foam had a mean that was almost 20 times higher. In this 

case, one of the two replicates had inhalable particulate results that were 25 times the first 

replicate; this single result greatly skewed the mean. While the replicate trimming 

operations were done by different workers, there were no differences observed in the way

they did the trimming that would account for such a large difference in the sample results. 

Interestingly, this is the only trimming situation where the source inhalable particulate 

results were lower than the personal inhalable particulate results. It is also interesting to 

note that the respirable particulate results were higher for the replicate with the lower 

inhalable particulate results.

RESPIRABLE PARTICULATE

 

The mean respirable particulate results for these short-term tasks were above the 

occupational exposure limit concentration (OSHA PEL = 5 mg/m38-hour TWA, ACGIH 

respirable particulate, not otherwise specified = 3 mg/m

3

;) only for the open cell foam, 

high dust potential techniques. Even so, the mean in this case exceeded the ACGIH

concentration by a factor of just 2.5. This result indicates that the particulate generated 

by all the trimming techniques is predominantly large.

INORGANIC PARTICULATE

 

Ashing of the PVC membrane filters from both the inhalable and respirable samples gave 

results that ranged from -9 to 0.9% ash. Since the range for four blank membrane filters 

that were ashed ranged from -2 to 0.7% ash, this result indicates that all of the 

gravimetrically measured mass was organic in nature. This is the expected result if all 

the particulate captured resulted from SPF insulation. This information will be useful in 
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later field sampling at actual construction sites, where a significant portion of the airborne 

particulate may result from non-SPF sources such as concrete and sheetrock. The ashing 

differential determination is designed to be a simple way to estimate the proportion of the 

mass measured that is not attributable to SPF.

CONCLUSIONS

The following conclusions can be drawn from the results in this study:

 The sampling and analytical techniques used appear to be practical and 

adequately sensitive for use in field evaluations of SPF insulation trimming 

exposures.

 While the SPF insulation trimming operations in this study were designed to 

simulate extreme case field situation, pMDI was not detected in any of the 

samples, indicating that exposure to these SPF components from trimming is not 

likely to be a concern when trimming is conducted with at least one hour cure 

after application.

 The inhalable particulate results were greater than the relevant occupational 

exposure guideline in all but one case, while the respirable particulate results were 

under the relevant occupational exposure guideline in most cases. The use of 

respiratory protection appropriate for particulates is indicated during SPF 

trimming operations.
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Appendix A

Protocol 1: DUST & MDI MEASUREMENTS DURING TRIMMING OF SPRAYED POLYURETHANE 

FOAM INSULATION

Objective

Evaluate the potential exposure of workers to inhalable and respirable polyurethane (PU) dust and 

pMDI during the post-application trimming / cutting of half pound open cell & two pound sprayed PU 

foam insulation (SPFI) in interior applications. 

1. Personal samples (within 30cm of the breathing zone) will be collected for total inhalable 

particulates (TIP), respirable particulates (RP) & pMDI on workers involved in cutting and 

trimming sprayed PU foam insulation to evaluate worker exposure potential.

2. Source samples (within 30 cm of the area being trimmed and downwind of it) will be collected

for TIP to measure the maximum concentrations of particulates produced by the trimming.

3. Sampling times will be as long as is reasonably practical (to increase sensitivity) and will be 

representative of the work practices undertaken by workers trimming sprayed PU foam 

insulation.

4. Target quantitation limits – inhalable / respirable dust: 1 g/m3, isocyanates: 5 g/m3.

SPFI Trimming Experimental Procedure & Sampling Plan

1. The experiment will be carried out in an SPFI development laboratory situation so that 

conditions can be controlled

a. No experiments will take place at least 24 hours before the experiment in same room 

and no experiments will take place during the test which could interfere with the tests.

b. Local exhaust ventilation will not be used.

c. Temperature, relative humidity, room air changes per hour, and room air current 

direction in the vicinity of the trimming will be recorded.

d. The application and trimming operations will be videotaped for documentation and 

explanation purposes

e. Area background (blank) samples (TIP, RP, pMDI) will be taken facing the room air 

current a few meters away from the operation before the SPFI is applied.

2. SPFI (a representative 1⁄2 lb or 2.5 lb formulation) will be applied to a model wall section using 

normal commercial application techniques and application rates. The SPFI formulation and 

application conditions will be chosen to produce foam with the highest potential to generate 

dust. The SPFI will be applied in such a way that post-application trimming will be needed. 

3. After a curing time of 1-2 hours, the foam will be trimmed using each applicable trimming 

technique (see table below). The techniques will be grouped into “low dust potential” and 

“normal dust potential” for each type of foam; a total trimming time of at least 15 minutes will 

be used for each dust potential technique category. The duration of use of each technique will 

be recorded.

Trimming Technique Dust 

Potential

1⁄2 lb (Open 

Cell) SPFI

2.5 lb (Closed 

Cell) SPFI

Foam Knife low X n/a

Foam Planer normal X X

Grinder / Sander normal n/a X

Hand Scraper (e.g., putty 

knife, curry comb, ice spud)

low X X
P

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4. A single personal sample of each type (TIP, RP, pMDI) will represent composite exposure 

during all the trimming operations for each dust potential category with the SPFI wall section.

5. A single source sample (TIP) will represent composite particulate concentration during all the 

trimming operations for each dust potential category with the SPFI wall section

6. Steps 2 - 5 will be repeated with the same SPFI formulation as a replicate. 

7. Steps 2 - 6 will be repeated with the remaining SPFI formulation.

Sampling Plan Summary

Sample Background Total (2 foams)

Type Normal Dust Low Dust Normal Dust Low Dust

TIP 1 2 2 2 2 17

RP 1 2 2 9

MDI 1 2 2 9

Background: 3 Source: 8 Personal: 24 35

Source Personal

Each Foam, in duplicate

Sampling & Analytical Methods

Particulates (TIP & RP)

1. TIP samples will be collected using IOM samplers equipped with appropriate membrane filters.

2. RP samples will be collected using appropriate membrane filters equipped with cyclonic preselectors operated at the flow rate to give the appropriate cutpoint.

3. The concentration of particulate deposited on the filters will determined gravimetrically using a 

microbalance.

4. Following the gravimetric determinations, the organic content of the collected particulate will be 

determined by ashing the filters, weighing the residue, and subtracting the residue weight from 

the original gravimetric weight.

5. Particulate sampling will be carried out in accordance with international standards, e.g.: 

a. ISO 15767:2009 - Workplace atmospheres. Controlling and characterizing uncertainty in 

weighing collected aerosols 

b. MDHS 14/3 - General methods for sampling and gravimetric analysis of respirable and 

inhalable dust.

c. CEN/TR 15230 - Workplace atmospheres - Guidance for sampling of inhalable, thoracic 

and respirable aerosol fractions

Polymeric MDI (pMDI)

1. pMDI samples will be collected using 13-mm samplers equipped with binder free GF filter 

impregnated with an appropriate derivatising reagent, e.g., 1,2MP, 1,2-PP, or MAP

2. After sampling, filters will be immediately desorbed in the field and returned to the laboratory 

for analysis.
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3. All samples will be analysed for monomeric MDI and MDI trimer using liquid chromatography 

4. pMDI sampling will be carried out in accordance with methods currently used by MDI 

producers in the US.