Safety precautions 4 Years, 6 Months ago
1. Dusts may be generated in several ways in advanced composite processes. The most common dust-generating processes are machining and finishing of cured parts and in repair of damaged parts. Much of the dust generated in these processes can be very fine and should be considered respirable. Studies of some graphite-epoxy finishing operations found respirable fractions ranging from 25% to 100%.
2. More dust is usually generated in finishing and repair processes since large surface areas are involved. Grinding, routing and sanding are frequently used methods in both processes. The repair process may require the use of abrasive blasting as well as sanding to remove existing paint or coatings. Typically, a synthetic blasting agent, e.g., plastic media blast, is used. Ingredients of the paint or coating being removed, such as lead or chromates, may also be of concern. The repair process may also require cutting or sawing to remove the damaged part area, and both may generate significant amounts of airborne dust.
3. In general, studies on composite dusts indicate that:
* The dusts are particulate in nature and usually contain few fibers;
* The dusts are thermally stable up to 250 °C and exhibit a high degree of cure; and
* Toxicology studies indicate the dusts should probably be controlled at levels below the PEL for inert dust, but not approaching the PEL for crystalline quartz.
1. Many of the solvents used in advanced composite processes are volatile and flammable. Most are skin and eye irritants, and some may be readily absorbed through the skin. Precautions must be taken when using organic solvents because they can facilitate the entry of toxic materials into the skin and organ systems. They may also enhance skin sensitization caused by the resin systems. Some (such as methyl alcohol) are poisonous, and all are capable of extracting fat from skin. Harmful effects from industrial exposures come principally from skin contact and inhalation.
2. Selection of the proper glove for protection is important. Permeation data are available for many industrial chemicals, especially solvents. However, in the case of resins and curing agents, not much data are available. This also is true for mixtures of solvents, as little or no testing has been done. Often the glove selection process is one of trial and error. If a skin rash or dermatitis is observed there are several possible causes:
* the wrong gloves may have been selected;
* improper work practices are being followed;
* the employee is deficient in personal hygiene practices; or
* adequate washing facilities are absent.
3. Several of the solvent classes most commonly found in the PMC workplace are listed below, along with general hazard information.
4. Several ketones are frequently found in PMC manufacture. These include:
* acetone (DMK)
* methyl ethyl ketone (MEK)
* methyl isobutyl ketone (MIBK)
These solvents may cause eye, nose, and throat irritation, and prolonged contact with the liquid may result in defatting of the skin and resultant dermatitis. In high concentrations, narcosis is produced with symptoms of headache, nausea, light-headedness, vomiting, dizziness, incoordination, and unconsciousness. Ketones are volatile and flammable. Acetone is a popular solvent used for cleanup and may be found around the workplace in containers for this purpose.
5. Some of the lower-boiling alcohols are sometimes used in composites manufacture. These include:
* methanol (methyl alcohol)
* ethanol (ethyl alcohol)
* isopropanol (isopropyl alcohol)
These alcohols do not usually present serious hazards in the industrial setting. Toxicity is usually related to irritation of the conjunctivae and the mucous membranes of the upper airway. Contact with the liquid may cause defatting of the skin and dermatitis. These alcohols are volatile and flammable.
6. Three chlorinated hydrocarbon compounds in particular are found in the composites workplace:
* methylene chloride (dichloromethane)
* 1,1,1-trichloroethane (methyl chloroform)
Health effects typical of the group include irritation of the eyes and upper respiratory tract, dizziness, confusion, drowsiness, nausea, vomiting, and occasionally abdominal pain. Visual disturbances may also occur. Due to the solvents' defatting properties, repeated or prolonged skin contact with these liquids may cause dermatitis. Ability to depress the central nervous system is a characteristic property of all members of this group.
These solvents are not particularly flammable. Many manufacturers have replaced the ketones with the above hydrocarbon solvents to reduce the risk of flammability.
Other solvents that may occasionally be used are:
* tetrahydrofuran (THF)
* dimethylsulfoxide (DMSO)
* dimethylformamide (DMF)
* gamma-butyrolactone (BLO)
* n-methyl pyrrolidone (NMP)
* n-butyl acetate
* glycol ethers
Technical literature including MSDS's from the solvent supplier should be consulted about these or any chemicals used with advanced composites.
Good workplace controls are essential in controlling exposure to process materials. Many of the materials, particularly the resins, curing agents, and fibers, present a potential dermal-exposure hazard. Many of the solvents and some of the curing agents present a potential inhalation hazard. Some materials present both a dermal and inhalation hazard. Ingestion may be a potential exposure hazard, but usually involves poor personal hygiene or contamination of eating facilities. The various types of workplace controls described below may typically be found in the advanced composite workplace.
1. ENGINEERING CONTROLS Isolation (e.g., isolated storage, separate process areas, enclosures, closed systems) and local exhaust ventilation are the primary engineering controls found in advanced composites processes. These controls can be found in:
* Resin mixing areas;
* Heated curing areas including autoclaves;
* Finishing and repair areas; and
* Controlling off-gases from exotherms
2. WORK PRACTICE CONTROLS Work practices, as distinguished from engineering controls, involve the way a task is performed. Some fundamental and easily implemented work practices that can be used to minimize exposures when working with advanced composites are:
* good employee training and education;
* following the proper procedures for production, process and control equipment;
* proper use, maintenance, and cleaning of personal protective equipment;
* good personal hygiene program;
* periodic inspection and maintenance of production, process and control equipment; and
* good supervision.
3. PERSONAL PROTECTIVE EQUIPMENT
1. Gloves, protective clothing, and eye protection may frequently be required, especially when working with resins, curing agents, and solvents. Selection of the proper protective materials should be based on permeation data, if available. This type of data are often available for the solvents used, but very little data are available for the resins and curing agents.
2. In many advanced composites processes several chemicals or mixtures are involved. There are essentially no permeation data available for chemical mixtures. This means that, in many cases, glove and clothing selection must be a trial and error process.
3. Generally, the resins are of a larger molecular size and so are less likely to permeate protective materials than the curing agents and solvents. The aromatic amine curing agents are particularly difficult to protect against. In some advanced composites processes, close hand work and contact is required, and a glove must provide good tactility. Often this type of glove provides the least protection against the resin and curing agent.
4. Eye protection can be provided by standard safety glasses with side shields, goggles, or a face shield, as needed.
5. Respiratory protection is not required in many advanced composites processes, due to the low vapor pressure of the materials involved. However, respirators may be required where:
* Airborne solvent levels are high;
* Dust levels are high (resin mixing, finishing, repair);
* Large surface areas and significant hand work are involved; and
* Exotherms are experienced.
4. ADMINISTRATIVE CONTROLS Employee exposures also can be controlled by scheduling operations with the highest exposures at a time when the fewest employees are present.