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Home | Spray Foam Industry | MDI and Respirator Safety
always wear a respirator

MDI and Respirator Safety

Are you wearing the correct respirator?

By Mike Bennett

The Spray Foam Coalition of the ACC Center for the Polyurethanes Industry defines spray polyurethane foam (SPF) as a spray-applied plastic that can form a continuous insulation and air-sealing barrier on walls, roofs, around corners, and on all contoured surfaces. Simply described, the process is this: Mixing and reacting unique liquid components — Part A and Part B — creates foam. The liquids react when mixed, expanding on contact to create foam that insulates, seals gaps, and can very quickly form moisture and vapor barriers. SPF insulation is known to resist heat transfer extremely well, and it offers a highly effective solution in reducing unwanted air infiltration through cracks, seams, and joints.


There are three primary types of SPF that can be used for insulation and other specific purposes. High-density spray foam, also known as closed-cell, is often used for exterior and roofing applications. Medium-density spray foam, also known as closed-cell, is often used for continuous insulation, interior cavity fill, and unvented attic applications. Low-density spray foam, also known as open-cell, is often used for interior cavity fill and unvented attic applications.


Spray polyurethane foam is a thermoset cellular plastic insulating material formed by combining methylene diphenyl diisocyanate (MDI) and a polyol blend. The reaction between these two materials releases heat in a process known as an exothermic reaction. In the United States, MDI is known as the A-Side and the polyol blend is known as the B-Side.


MDI (A-Side or Isocyanate Side)
MDI has a potential risk of causing irritation and sensitization through inhalation and skin contact. MDI exposure can affect skin, eyes, and lungs. Once sensitized, continuing MDI exposure can cause persistent or progressive symptoms and even life-threatening asthmatic reactions. Sensitized people should be removed from environments and activities in which they could be potentially exposed to MDI. Always wear the proper personal protective equipment (PPE) when working with MDI. Always refer to the manufacturer’s Material Safety Data Sheet (MSDS) for detailed information on potential health effects of any chemicals present on the jobsite.


Polyol Blend (Resin or B-side)
The B-side formulations for SPF use five basic chemical classes: Polyols, blowing agents, catalysts, flame retardants, and surfactants. The polyol blend has a potential health risk of irritation to the respiratory system, skin, and eyes. Always wear the proper PPE when working with polyol blends. Always refer to the manufacturer’s MSDS for more detailed information on potential health effects of any chemicals present on the jobsite.


Properly designed ventilation can reduce levels of airborne aerosols, mists, and vapors that are generated during spray application. This can help protect SPF applicators, crew members, and others who may be working in adjacent areas. During and after spray application, vapors and mists, as well as particulates and dust from trimming or sanding the foam, can linger until the area is ventilated and fully cleaned. Carefully schedule construction activities so that no other trades or occupants are in the area during SPF installation.

During application, airborne levels may exceed the exposure guidelines; therefore, always use proper PPE. OSHA’s Respiratory Protection Standard (29 CFR 1910.134) establishes the requirements for respiratory protection. Supplied-air respirators (SAR) are typically used in interior applications. Air purifying respirators (cartridge respirators) may be adequate in exterior (outdoor) applications. Refer to the NIOSH Respirator Decision Logic for more information regarding respirator selection at


The OSHA Respiratory Protection Standard (29 CR 1910.134) requires employers to have a written respiratory protection program outlining when employees are required to use respiratory protection. The Standard outlines requirements for respirator selection, respirator maintenance, annual fit testing, medical evaluation, and annual training.



When using High-Pressure Supplied-Air systems, a compressor that can provide the worker a minimum of six cubic feet of air per minute (CFM) is essential. The total number of workers and tools to run off of the compressor determines what size compressor a company will need. To be safe when selecting a compressor, make sure the compressor can supply a minimum six CFM of air to the worker, in addition to supplying all of the other equipment that you may be running off
of that same compressor.

The size of the compressor is critical in a supplied-air system to make sure each worker gets enough air flow. This system consists of an air filtration panel, CO monitor, hood or full facepiece, 50 feet of hose, and potentially, an air cooler,
if the end user is working in a hot environment. The air filtration panel converts the air coming from the compressor and turns it into Grade D Breathing Air by: Filtering any moisture out of the air, filtering any particulates out of the air, and filtering any organic vapors out of the air. The filtration panel will also alarm if the CO in the air is too high. Grade D Breathing Air is defined by NIOSH as containing 19.5 to 23.5 percent O2, 5mg of Hydrocarbons, 10ppm maximum of CO, 1,000ppm of CO2, no odor or taste, and no toxic contaminates. The advantages of these compressed air systems are:

  • System is good up to 300 feet;
  • Air cooler can be attached if needed;
  • Hood or a tight-fitting, full-face piece can be worn;
  • System filters moisture, particulates, and any organic vapors in the air;
  • System has a CO2 monitor that alarms if the CO level from the compressor is too high;
  • Can easily convert full facepiece respirator from supplied air (SAR) to air purifying (APR) respirator.


For situations that call for ambient-air supplied-air, typically interior applications, systems such as Honeywell’s Safety Ambient-Air Supplied-Air Systems consist of a ¾ to 1.5 HP ambient air pump, hood or full facepiece, and 50 feet of hose. In these systems, the ambient air pump takes surrounding air, filters out any particulates, and then pushes the clean air through the hose to the workers. The worker can only work 50 to 100 feet from the ambient air pump. These types of systems are commonly referred to as Supplied Air Respirators (SAR). The advantages of these ambient-air supplied-air systems include the facts that:

  • System will work at distances of 50- to 100-feet depending on pump size;
  • Portable system so you can move from room to room;
  • Must have fresh air for the ambient air pump to filter;
  • Hood or tight-fitting full facepiece can be worn;
  • Can easily convert from SAR to APR.



When working in an exterior setting — especially in windy conditions — it is best to use a powered air purifying respirator. These respirators are designed for use in open-air environments, as they utilize a blower, which pulls in contaminated air and filters it through a cartridge and filter depending on the contaminant present. Honeywell’s PAPR system, the CA200 Compact Air Purifying Respirator, is designed specifically for use in exterior spray foam applications. The advantages of a PAPR system include the following features:

  • These systems eliminate extra air hoses that can sometimes get in the way;
  • Systems have audible, visual, and vibrating alarms;
  • Hood or tight-fitting full facepiece can be worn.


Full facepiece respirators with cartridges are typically worn during spray foam applications as long as the worker is not the one spraying the foam. The spray foam applicator must wear a supplied-air respirator. The full facepiece is typically worn by the adjacent crew member who is helping the sprayer maneuver the hoses or who is holding the windscreen to block overspray. The full facepiece respirator is also worn in open-air spray foam roof applications.


Regardless of your role on the team, if you spray foam, you must wear protection. The alphabet soup of chemicals present pose too great a risk to your health. Determine which respirator fits your need, and then be sure to properly wear it. •

Photos courtesy of Honeywell

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