Emissions from Resin Transfer Molding (RTM) and Infusion

When considering styrene emissions from an RTM or infusion process, there are four potential sources of process emissions: 1. The transfer of resin from the original container (drum, tank, etc) to the working tank. 2. The air that is displaced by resin injected in the mold (or discharged via vacuum pump in vacuum infustion). 3. Incidental resin leakage at the injection port. 4. Mold perimeter leaks.

Assuming that resin handling does not produce any spills, that the containers are kept covered except during the actual transfer, and that the mold does not leak around the parting line, then the only source of emissions is air escaping from the mold cavity and some minor dripping at the injection point (and for infusion, emission in the vacuum pump exhaust).

Emissions from this process have generally been reported at 1% of the styrene weight. The RTM emissions factor continues to be the best available data and therefore is acceptable for reporting emissions from RTM and infussion processes.

The emissions calculation would be:

Weight of Resin Consumed X % Styrene Monomer X 1% Emissions Factor = Emissions by Weight

Example: 100 lb. Resin used; Styrene content = 40% 100 lb. X 40% monomer X 1% Emiss. Factor = 0.4 lb Emissions

Storage of resin in intermediate bulk containers (totes)

At http://www.nfpa.org/ibc, the National Fire Protection Association cautions,

​Intermediate Bulk Containers (IBCs) [commonly called totes] containing combustible or flammable fluids can cause dangerous fires when improperly stored in warehouses and chemical facilities​, ​

and,

Pool fires [from punctured IBCs] can occur faster than the fire protection system can respond and control them, and become catastrophic events as a result.

 

  

Exposure to silica

Many composite raw materials and molded composite products contain crystalline silicaAccording to OSHA's special topics page, prolonged inhalation to crystalline silica at high concentrations may lead to the development of disabling and sometimes fatal lung diseases, including silicosis and lung cancer.


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Sand, quartz, calcium carbonate, gypsum, dolomite, mica and other materials used in the production of cast polymer, engineered stone, tub/showers and many other composite products contain crystalline silica. Glass fibers and fumed silica are forms of amorphous silica and are not considered toxic except possibly as a nuisance dust (classified as "particulates not otherwise regulated" in OSHA's Table Z-1 on air contaminants). The term "silica" in OSHA regulations and other references to workplace health and safety typically refers to crystalline silica.

OSHA's 2008 national emphasis program on crystalline silica identifies its use as a functional filler in the manufacture of plastics as a major source of exposure. The cutting of granite is also identified as a source of silica exposure.

OSHA's exposure limits for crystalline silica are provided in the agency's Table Z-3 on mineral dusts.

OSHA's proposed silica standard

In August of 2013, OSHA released a proposed new regulation (officially released in a Sept. 12, 2013 Federal Register notice) to control occupational exposure to respirable crystalline silica. The deadline for submission of written comments on the proposal will be 90 days following publication in the Federal Register. OSHA plans to hold a workshop to collect additional stakeholder input in March, 2014.

Under the OSHA proposal, employers would be required to conduct an initial assessment of occupational exposure to silica. If 8-hour weighted average exposures exceeded an action level of 25 µg/m3 (micrograms respirable crystalline silica per cubic meter of air), the employer would be required to implement a periodic monitoring program.

For workplaces where 8-hour weighted average exposures exceed a revised permissible exposure limit (PEL) of 50 µg/m3, employers would be required to install engineering controls and adopt workpractices to reduce exposures to the extent possible. Job rotation would not be permissible as a technique to reduce silica exposures.

If exposures still exceeded the PEL after installation of engineering controls and adoption of workpractices, personal protective equipment (PPE) could be used to meet the PEL. Employers must establish procedures to prevent unauthorized employees from entering areas where they might be exposed to silica in excess of the PEL. Regular medical monitoring of employees would be required. 

All exposure assessments would be conducted in the workers' breathing zones, but without PPE. Exposure testing would be conducted by specialized accredited laboratories. Exposure assessments would be measured and calculated as 8-hour time weighted averages.

Under the agency's hazard communication program, employers would be required to inform workers and provide training and equipment to control silica exposures. Warnings would also be provided to employees of customers who may be exposed to silica as a result of working with engineered stone or other composite products. OSHA's proposed rule identifies the manufacture and cutting of engineered stone as a source of silica exposures.

In the detailed but important technical and economic analysis supporting the rule, OSHA provides a list of likely compliance methods, as well as feasability and cost analyses. (A summary of sections that likely apply to cast polymer and post-mold operations for composite laminate is available here.) For small companies, OSHA estimates the average annualized cost of compliance with the proposed silica standard to be $4,284, amounting to 0.25% of revenue and 4.51% of profits.

Health impacts

OSHA estimates the lifetime risk of workers dying from cancer as a result of workplace exposure to respirable cystalline silica is reduced from a range of 13-60 cases per 1,000 workers under the current PEL, to a range of 6-26 cases per 1,000 workers under the proposed revised PEL. In the preamble to the proposed rule, OSHA also provides estimated reductions in deaths due to silicosis and renal disease, and in incidents of non-fatal silicosis.

The table below presents OSHA's estimates of health impact per 1,000 workers exposed over 45 years, for the current PEL, the proposed PEL and the proposed action level. The table also compares the worker health benefit OSHA expects under its silica rule to the benefits achieved under its asbestos and methylene chloride standards.

Silica - Summary of OSHA Risk Assessment

American Society of Civil Engineers

Load Factor Resistant Design (LFRD)
The Pultrusion Industry Council (PIC) of the American Composites Manufacturers Association (ACMA) and the American Society of Civil Engineers (ASCE) worked together to develop the first design standard for pultruded composites. This 3-year project, financially supported by the PIC members, resulted in the development of a “Pre-Standard for Load & Resistance Factor Design (LRFD) of Pultruded Fiber Reinforced Polymer (FRP) Structures,” ASCE served as the project manager in the development of the standard.

Currently, this Pre-Standard document is following the standards development process by ASCE and ANSI to promulgate this into an official ASCE Standard. The ASCE Fiber Composites and Polymers Standards Committee has the responsibility to review and ballot the Pre-Standard.

The LRFD standard will establish material properties for pultruded FRP composites that will allow architects and structural engineers to use pultruded FRP products with confidence.

LRFD Standard Outline

  • Chapter 1. General Provisions
  • Chapter 2. Design Requirements
  • Chapter 3. Design of Tension Members
  • Chapter 4. Design of Compression Members
  • Chapter 5. Design of Members for Flexure and Shear
  • Chapter 6. Design of Members Under Combined Forces and Torsion
  • Chapter 7. Design of Plates and Built-Up Members
  • Chapter 8. Design of Bolted Connections

Pre-Standard Authors

  • Dr. Bruce R. Ellingwood, Georgia Institute of Technology
  • Dr. Abdul-Hamid Zureick, Georgia Institute of Technology
  • Dr. Hota V. S. GangaRao, West Virginia University
  • Dr. Roberto Lopez-Anido, University of Maine
  • Dr. Lawrence Bank, University of Wisconsin at Madison (supported by Dr. J. Toby Mottram, Warwick University (UK), Dr. Russell Gentry, Georgia Institute of Technology, Dr. Carol Shield, University of Minnesota, and Michael McCarthy, University of Wisconsin)

Engineers, architects, and designers may request a complimentary copy of the LRFD PreStandard by contacting John Busel at jbusel@acmanet.org

Other Books related to Composites Design, Standards, and Specification

  • Design of Fiberglass-Reinforced Plastic (FRP) Stacks (52-10) - This Standard outlines the important mechanical and structural engineering considerations for stacks where the primary supporting shell is made of FRP.
  • Design Guide for FRP Composite Connections - This Manual of Practice covers major issues related to the analysis and design of composite joints and frame connections manufactured from fiber-reinforced polymer (FRP) composites in general and pultruded (PFRP) composites in particular
  • Recommended Practice for Fiber-Reinforced Polymer Products for Overhead Utility Line Structures - Manuals of Practice (MOP) 104 - This Manual details best practices for the use of fiber-reinforced polymer (FRP) products in conductor support applications and FRP poles.
  • Composites in Construction - This collection contains 29 papers that address the state of the art in fiber-reinforced polymer (FRP) composites for use in construction.
  • Gap Analysis for Durability of Fiber-Reinforced Polymer Composites in Civil Engineering - This report provides the results of a study on what is known and not known about the use of fiber-reinforced polymer (FRP) composites as a material for civil infrastructure. As FRP composites are increasingly used, the lack or inaccessibility of data related to the their durability is proving to be a major obstacle to widespread acceptance and implementation of these materials. This report provides the results of a "gap analysis" to identify critical areas in which data is needed to assist with specific applications.
  • Structural Plastics Selection Manual - Manuals of Practice (MOP) MOP 66 - Structural Plastics Manual presents information for the structural engineer regarding the selection of the proper material or combination of materials that will provide those properties (mechanical, physical, thermal, or whatever) upon which design assumptions and calculations are based.