Despite the increased use of solvent-free products and materials in today's roofing industry, the prevalence of solvent-induced neuropathy among roofers is still startling. As far back as 1987, the National Institute of Occupational Safety and Health (NIOSH) estimated that almost 10 million workers in the United States were exposed to potentially harmful levels of organic solvents in the workplace every year. An organic solvent is a liquid that is used to dissolve other liquids. They work on the principle that "like dissolves like" so the two major categories of roofing solvents are hydrocarbons (benzene, toluene, n-hexane, xylene, kerosene and mineral spirits) and ketones. (methylethylketone and acetone).

The roofing industry has many solvent-bearing products in prevalent use today, including: cutback asphalt, blind nailing asphaltic cements, lap and flashing adhesives, seam adhesives, cold-applied products, solvent-borne dampproofing, thinners, cleaners, degreasers and fuels. Generally speaking, solvent vapors have a low flash point and large explosive range (between upper and lower flammable limits) when combined with oxygen in the air.

Neuropathy is a medical term defined as any disease affecting the nerve tissue of either the central nervous system or peripheral nervous system. Unlike the peripheral nerves, the central nervous system is incapable of regeneration or supplementation after disease or injury. The exposure effects may be either acute, with an immediate onset of symptoms, or chronic in nature, where the symptomatic health effects may take months or even years to develop and be recognized.

There are several specific neuropathic diseases that occur most often due to solvent exposure. Toxic neuritis is an inflammation or degeneration of nerve fibers resulting from an exposure to a chemical toxin in sufficient concentration and exposure time (dose). Solvent neuritis may often cause acute peripheral nerve damage to the lower extremities while constant exposure to solvent vapors above the permissible exposure limit may lead to some serious chronic complications involving the central nervous system. Neuralgia is an intense, but often localized pain perceived along the affected pathway of an inflamed nerve sheath. Neurotoxic-dermititis is a common subtype of neuralgia with localized inflammation caused by neural damage just beneath the exposed skin.

A Few Suspect Solvents

Some of the common scientific terms you might run across when reading the MSDS for products containing these chemical substances may appear daunting at first. But their meanings are very important to understand if an employer is going to adequately protect his employees from hazardous solvent exposures. Permissible Exposure Limit is OSHA's and NIOSH's published concentration (in parts-per-million parts of air or percent volume of total air) above which the employer of exposed workers shall protect them, by means of engineering, administrative or personal protective equipment controls or a combination of all of them. Recommended Exposure Limit is NIOSH's time-weighted average exposure to a chemical for a 10-hour day, 40-hour workweek. Whenever evaluating either permissible or recomndded exposure limits, always choose the lower value as a safe working exposure. Ceiling Limit is a recommended exposure limit (NIOSH) that should not be exceeded at any time. Threshold Limit Value is established by the American Congress of Government Industrial Hygienists as the concentration of a hazardous substance. Both values are considered time-weighted averages based on an eight-hour sample exposure for a 40-hour workweek. While actual real-time exposures to the solvents may be higher or lower than these values, the average concentration over eight hours must not exceed them. Short Term Exposure Limit is defined by OSHA as that maximum concentration of a substance to which an employee may be exposed for a period of not more than 15 minutes, no more than four times in an eight-hour shift with at least 60 minutes of fresh air respiratory rehabilitation between exposures. Immediately Dangerous to Life or Health is the very highest level determined by NIOSH to which an employee may be exposed before: irreversible health effects are determined probable; the risks of a fatality have become dangerously high; or the ability of the worker to escape further exposure has been critically impaired, prohibiting self-rescue.

Hazard Identification

As noted in the solvent hazard Table 1, the most common route of entry for solvents is inhalation. Be cautious whenever you are welding, grinding, heating or burning any solid materials that may be been previously saturated with a solvent. The fumes and particles may become just as hazardous when inhaled as the solvent itself. Most often these exposures result in symptoms such as headache, dizziness, confusion and drowsiness. There is often a significant anesthetic reaction to the olfactory nerve. In this case, odor intensity is not a good indicator of toxicity. More could mean less and less could be more.

The second most common route of exposure is by skin contact with the liquid and direct absorption into the dermal tissue and subcutaneous capillaries. Solvents pass easily through unbroken dermis and epidermis layers by capillary action. Rapid absorption is also common through the mucous membranes of the nose and throat. Even vapors trapped behind contact lenses on the corneas pass easily and directly into the lymphatic and circulatory systems.

Solvent-induced neuropathy is often readily diagnosed by intense burning and redness of the affected areas. Irritated skin should be immediately and thoroughly flushed with potable water for 15 minutes minimum. Always seek prompt medical attention whenever solvent poisoning is suspected as the effects may be delayed and the damage prolonged. Never use gasoline, kerosene or other solvents to remove tar and adhesive from your skin or clothing. It is the Competent Person's duties to select the specific gloves and chemical protective clothing to protect the worker from reaction or breakthrough by the solvents. The proper personal protective equipment is selected on the basis of the type and concentration of the solvent as described in its MSDS as well as the assumed period of the worker's exposure.

The third most prevalent route of exposure is by ingestion, whether it is direct contact on the lips or eating utensils or drinking vessels or simply casual hand/mouth cross-contamination. Cigarette smoking and makeup application may also lead to ingestion of solvent-contaminated materials. Regrettably, a great many solvent-based illnesses occur year after year when substances are temporarily stored in cups and glasses, left unattended and mistakenly ingested by an unsuspecting victim.

Injection is the fourth most common route of entry for solvents and other toxins into the body. It is usually assessed as contamination by way of a cut or laceration or some other impalement wound. Even violent chemical reactions and explosions can cause solvents to become injected by means of shrapnel. Never use compressed air to clean your body or your clothing as the air pressure may be adequate to inject any contaminate on your skin or clothing into you capillaries below. Air embolisms have also been documented as contributing to strokes, seizures and even death.

Solvents are divided into two basic classifications: organic and aqueous. Organic solvents bear carbon molecules in their structure. These are the solvents that are most commonly found on the roof job. Although other organs are directly affected, the predominant damage is incurred by the central nervous system. Aqueous solvents are compounds that contain water. Acid and alkalis are classified as aqueous solvents. In most cases, engineering controls such as ventilation are preferred over personal protective equipment such as gloves, clothing and respirators.

Solvent Symptomology

Primarily, how well the body accepts a toxic substance depends on five major factors: The type of substance The concentration of the substance The amount (or dose) of the substance absorbed The time period over which it is absorbed The susceptibility (or sensitivity) of the individual exposed.

Most solvents have a high evaporation rate and a vapor density much less than air. This enables us to inhale their vapors quite easily. Solvents have a high permeability rate in dermal contact and are readily absorbed into the bloodstream. Once our tissues are saturated by these substances, the acute symptoms of solvent poisoning may be easily identified. Not all solvents have the same neurotoxic effects on everyone but some acute and chronic symptoms may include: 1. Initial feeling of euphoria, "drunken" stupor, confusion and disorientation 2. Nausea and gastrointestinal distress 3. Numbness of the feet and hands 4. Muscle weakness in the feet and lower legs (eventual paralysis) 5. Jaundice 6. Loss of consciousness and coma 7. Cancer

The procedures undertaken by the Competent Person for personal protective equipment always start with substance identification. What class of solvent are we about to work with today? How much will I need for my immediate task?

Next, the airborne concentration of the substance should be determined either by direct-reading instruments or else by grab sampling the substance and having it analyzed. Once we've identified the solvent or solvent-borne materials we are working with as well as its concentration, we must take some logical precautions and conduct our operation incorporating safe solvent work practices: 1. The safest work practice is to REPLACE the solvent with a less hazardous product whenever it is feasible and doesn't create a greater hazard. Select low or no-VOC emitting materials, glues and adhesives when possible. In some cases, just "airing out" solvent-bearing materials briefly will minimize exposure. 2. Have a Competent Person regularly inspect the worksite for safe solvent usage and grab-sample the atmosphere to monitor workers' exposures to ensure engineering controls are effective. 3. Train workers in site-specific hazardous materials and their appropriate controls according to your firm's hazard communication program. As an administrative control, share tasks using solvents among different well trained and experienced personnel. 4. Identify the potential hazard before exposure occurs. Become familiar with the chemical substance before you use it. Update and read the MSDS repeatedly until all of its properties become familiar. 5. Train and equip all your personnel in your firm's Respiratory Protection Program. Ensure solvent workers are medically evaluated and properly fit-tested for the appropriate respirator device. Document the Maximum Use Concentration and assigned protection factor for each type of respirator. Develop a well-researched cartridge change-out program based on the site conditions, work tasks and air monitoring conducted by the Competent Person. 6. Even on a roof, high concentrations of organic solvent vapors can occur and natural air convection may prove insufficient. Installation of dilution fans may prove effective in reducing the health and fire hazards from such captured vapor concentrations. 7. Be aware of the natural convection airflow direction and post appropriate warning signs in any area where others might produce any ignition source, such as welding, grinding or electrical arcing of power tools. 8. Notify other workers and pedestrians around you that you are about to work with a potentially toxic substance with a low flash point. They might wish to adjust their own work practices to avoid the hazard 9. When working on occupied structures (schools, hospitals, offices) always identify the air handling and HVAC units and take precautions to isolate solvents and their vapors from migration indoors. 10. Attempt to work during the building staff's off-duty hours whenever practical to minimize exposures. 11. Identify a Competent Person to answer indoor air quality questions during your site work. Provide building occupants any MSDSs requested. Encourage building tenants to report all complaints, symptoms and observations to your Competent Person and thoroughly log all reports. 12. Look for open windows or doors as well as any major or minor roof penetrations through which solvent materials or vapors may potentially migrate. 13. Enforce good housekeeping practices. Clean up solvent cans, rags and materials often (more than once a shift) and deposit them in a clearly labeled HazMat container (not in the dumpster) located in a safe area away from other fuels, oxygen bottles, flammable materials egress doors and stairs. Empty trash cans often (end of shift). Be aware that solvent saturated rags are prone to auto-ignition and should be placed in an NFPA-certified combustible material container capable of withstanding an incipient fire. 14. Practice common sense when providing first aid to a symptomatic worker, but always call 911 and the local Poison Control Center whenever solvent exposure symptoms become serious or prolonged. Always bring the MSDS with you for any emergency room treatment. Study the initial symptoms of exposure and be aware of the manufacturer's recommended first aid treatments if an exposure does occur. If first aid or CPR is required, be sure the first responder is not exceeding his/her current level of training. 15. Closely observe any written warnings or safe handling practices noted on the product's label. 16. Do not eat, drink, smoke or use make-up around a solvent-laden environment. 17. Avoid wearing contact lenses near potential solvent vapors as they can trap contamination and promote absorption. 18. Always decontaminate yourself by changing out of your work clothes and washing up thoroughly after working with solvents. Prevent yourself from bringing these hazards into your family's environment. 19. Ensure your workplace is well ventilated. Even a roof can be hazardous if the air is trapped by surrounding buildings or structures. 20. Never sniff (or waft) any chemical toward your face in order to identify its nature or detect its location. Sometimes a little may prove to be too much. 21. Properly use, fit-test, inspect, maintain and understand the personal protective equipment provided by a Competent Person. Remember all personal protective equipment is designed to fail, not succeed. It is your Competent Person's duty to understand, predict, and prevent its failure or break-through. 22. Never put your hands directly into any solvent solution, even if wearing gloves. The risk always outweighs the benefit. 23. Contain solvent spills or discharges if they are small and clean up immediately with precaution if you are adequately trained for such procedures. Always post warning signs, ventilate and wear the proper personal protective equipment before clean-up operations. 24. Use caution when disposing of used solvent containers. The lower explosive limit is often reached when the container is almost empty. An un-vented empty solvent can set out on dark roof deck in the afternoon summer sun may result in a startling explosion. Containers may appear to be empty but serious hazards may still exist for both the worker and the environment. 25. Become familiar with the reactions that may occur with your solvent and other substances and never discount any potential route-of-entry.