Reducing occupational exposure to polyurethane foam dust

Polyurethane foam (PU) is found in many consumer and industrial products on the market today. From furniture and bedding to packaging and automotive liners, PU is known for its durability, comfort and support.⁵

According to the Polyurethane Foam Association, approximately 1.7 billion pounds of foam are produced and used each year in the U.S.

While there are different types and uses for foam, the basic production method is the same.

Flexible PU foam is produced from a reaction of two key chemicals, a polyol and an isocyanate with water. These are mixed together vigorously in high intensity mixers in specific amounts with other ingredients, and the foam reaction begins almost immediately. Bubbles are formed and the mixture expands.⁷

Once the reaction is complete, the foam can be shaped and manipulated depending on its final use. A common method of foam manipulation is shaping through sanding or grinding. This process generates large amounts of PU dust.

A short video on YouTube demonstrates a planer or belt sander smoothing out a large piece of flexible polyurethane foam. As you can see from this screenshot, dust is dispersed and accumulates in the air and on surfaces.

Video Source: http://youtu.be/vBeXalRiTBw

Polyurethane dust inhalation

If you examine a Material Safety Data Sheet (SDS) for cured flexible PU foam, you will see caution statements such as these:

• The primary adverse health effects of this material are related to the dust created by sanding, grinding or cutting the cured foam. Mechanical ventilation or exhaust should be provided during this type of use/activity.³
• Inhalation: May irritate mucous membranes with tightness in chest (This only if dust is created during cutting, sanding or grinding of cured foam).³
• Adequate ventilation should also be employed so that dust levels do not exceed recommended guidelines.³

Multiple studies have been done regarding potential health effects of respirable dust.

One study in particular examined dust emission during the cutting of polyurethane-impregnated bandages in a hospital environment.¹

When hospital staff removed splinting bandages with a power saw, a large amount of dust was generated. While the PU-impregnated bandage produced a lower airborne dust concentration than other bandage materials, the size and nature of the dust became a concern.

Like all particles, their aerodynamic diameters determine if and for how long they remain airborne, their likelihood of being inhaled, and their site of deposition in the respiratory system [respirable dust].⁶

In the study’s findings, 90% of the particles in the dust cloud generated by the PU-impregnated bandage were considered respirable and contained fragments of PU resin.

In another study, laboratory rodents where exposed by inhalation to polyurethane foam particles (20 mg/m³) for 5 days/week for 6 weeks.²

Early findings showed the particles had deposited in the respiratory bronchi and in the subpleural alveoli. Six months after initial exposure, slight thickening of the alveolar walls occurred. Within nine months the fibrosis had progressed and at 12 months small scars consisting of fibrous tissue nodules developed.

Health effects of respirable dust

The side effects of inhaling polyurethane dust are not entirely unique, as similar effects have been documented for exposure to a variety of particulate matter [dust].

While OSHA and other regulatory agencies have established strict exposure limits for carcinogenic dusts like silica, a majority of general dust falls into a category called “particulates not otherwise regulated”. For the most part this encompasses respirable dust not considered to be a human carcinogen.

Particulates not otherwise regulated (respirable fraction)⁴

While “general” dust particles may not directly cause cancer, their long-term effects on the body warrant concern.

Health effects resulting from exposure to dust may become obvious only after long-term exposure; this is often the case with pneumoconioses. It may happen that effects appear even after exposure has ceased, thus being more easily overlooked or mistakenly attributed to non-occupational conditions.⁶

Source capture engineering controls

While it is good practice to capture ambient room dust, it is even more vital to capture dust at the source of emission.

The World Health Organization (WHO) compiled a document regarding prevention of airborne dust in the workplace.⁶ Many important observations and recommendations can be found in the document including:

• A dust release can be localized and only affect the immediate worker, or it may spread throughout the workplace and affect everybody else.
• Unless its generation is prevented or it is removed from the air, dust may move with ambient air and reach even persons who are remote from the source and whose exposure is unsuspected.
• Containment consists in placing a physical barrier between the substance and people, for example putting a process inside a box. It is usually necessary to have a ventilation system that keeps the enclosure under negative pressure, so that there is no emission at cracks or at points where material moves in or out of the enclosure.

Engineering Safety Control

Sentry Air Systems offers a variety of source capture engineering safety controls that aid in the prevention of respirable dust exposure.

We recently designed this conceptual drawing for a customer’s polyurethane dust application involving the grinding of flexible PU foam for automotive liners.

70-inch DFE-D ducted to Model 500 air cleaner

This configuration includes a standard 70-inch wide dual exhaust hood that has been ducted to our Model 500 Industrial Air Cleaner with a dual outlet plenum and cleanable micro-pleat series filters.

This custom configuration allows the operator to sand and grind the sheet of PU foam while the negative pressure system uses up to 1,300 CFM to pull dust through the ductwork and into the air cleaner.

The micro-pleat series filters work to scrub the air of dust contaminants before recirculating the cleansed air back into the room.

The filters easily clean with pressurized air and excess dust and waste falls into the unit’s internal dust pan allowing for easy disposal.

Contact Sentry Air

For more information about controlling polyurethane dust exposure or other occupational respiratory hazards, contact Sentry Air Systems at 800.799.4609, email sales@sentryair.com, visit our website or fill out the feedback form below.

Resources

¹Wytch, R., Ritchie, I., Clayton, R., Gregory, D., & Wardlaw, D. (1988). Dust emission during cutting of polyurethane-impregnated bandages. Prosthetics and Orthotics International, 12, 155-160.

²Stemmer, K., Bingham, E., & Barkley, W. (1975). Pulmonary Response to Polyurethane Dust. Environmental Health Perspectives, 11, 109-113.

³Material Data Safety Sheet – Rigid Polyurethane Foam. (1995, October 1). Retrieved September 12, 2014, from http://tigerfoam.com/PDF-FILES/MSDS_CURED_FOAM.pdf

⁴ Chemical Sampling Information Particulates Not Otherwise Regulated (Respirable Fraction)

https://www.osha.gov/dts/chemicalsampling/data/CH_259635.html

⁵ Polyurethane Applications: http://polyurethane.americanchemistry.com/Introduction-to-Polyurethanes/Applications

⁶ Hazard prevention and control in the work environment: Airborne dust. (1999). Geneva: World Health Organization (WHO). http://www.who.int/occupational_health/publications/en/oehairbornedust.pdf

⁷ Flexible Polyurethane Foam: A Primer. (1991, February 1). In Touch: Information on Flexible Polyurethane Foam. http://www.pfa.org/intouch/new_pdf/lr_IntouchV1.1.pdf