Tampa Paving - Types Of Paving
Types of Paving...
Asphalt is a dark brown or black substance derived from crude oil. It may be a solid, a semi-solid, or a
liquid and is a strong adhesive.
Asphalt is often mistakenly confused with "tar", "coal tar", or "pitch" because the appearance is similar
and the substances may be used interchangeably in many industrial processes. Tar and pitch are derived from
coal products which are chemically and physically different.
Other names for asphalt include road tar, road binder, mineral pitch, petroleum pitch, petroleum asphalt,
and seal-coating material.
Asphalt is used for road paving, roofing tar, roll-roofing, roofing felt, shingles, pipe covering, floor
tile, waterproofing, and many other products and processes. Its use will determine what other substances are
blended with it and what health and safety hazards are associated with it.
There are two main types of asphalt:
- Straight-run asphalt or asphalt cement: Straight-run asphalt is used for paving roads,
airport runways, and parking lots. Because of its solid to semi-solid nature, it must first be "cut" with a
solvent to bring it to a more liquid state; this is known as Cut Back Asphalt. Highway workers are most
likely to use straight run asphalt.
- Air-blown or oxidized asphalt: Air-blown asphalt has a high softening point and is
used primarily in roofing, pipe covering, and similar situations.
There are two main hazards associated with asphalt:
- Fire and explosion hazards, and
- Health hazards associated with skin contact, eye contact, and/or inhalation of fumes and vapors.
Fire and Explosion Hazards
Most of the fire and explosion hazard associated with asphalt comes from the vapors of the solvent mixed
into the asphalt, not the asphalt itself. The hazard is determined by the flammable or explosive nature of the
solvent used and how fast it evaporates. The flashpoint (FP) of a chemical or mixture is the combined
measure of this flammable or explosive potential. The flashpoint is the lowest temperature at which enough of
the chemical evaporates to form a mixture with air which can be ignited by a spark. The lower the flash point,
the higher the fire and explosion hazard. If the flash point is below the room temperature, the chemical is a
The flash point — and therefore, the fire or explosion hazard — can partially be determined by the type of
asphalt used. There are three types of cut asphalt. The type and amount of solvent (or oil) added determines
the properties of the final mix.
- Rapid-Curing Asphalt (RC) is a blended asphalt which has been "cut" with a "low-flash" (highly
flammable) petroleum solvent. This low flash solvent quickly evaporates, allowing the "RC" mixture to
rapidly set and harden. Examples of solvents commonly used in "RC" mixtures include: Benzene
(FP=12°F), Dioxane (FP=54°F), Toluene (FP=40°F), Xylene (FP = 81-90°F), and
Naptha (FP = 107°F).
- Medium-Curing Asphalt (MC) is a blended asphalt which has been "cut" with a solvent with a
flash point over 170°F.
- Slow-Curing Asphalt (SC) is a blended asphalt which has been "cut" with a low-flash oil having
a flashpoint of over 250°F.
The FP of the asphalt and solvent mix will be higher than the FP of the solvent alone. Remember, the lower
the FP, the greater the explosion hazard. Table 1 illustrates the various grades of RC, MC, and SC asphalt
mixes and their relative flash points.
FLASH POINT REQUIREMENTS
FOR ASPHALTIC MATERIALS*
|Type and Grade of Material
Flash Point (deg.F)
|Rapid-Curing Liquid Asphalt
|Grades RC-250, 800, and 3,000
|Medium-Curing Liquid Asphalt
|Grade MC-250, 800, 3,000
|Slow-Curing Liquid Asphalt
|Grade SC- 70
| * Adapted from NSC Data Sheet 1-215-80, Asphalt.
HEALTH HAZARDS OF ASPHALT
- Acute (short-term) Health Effects: Skin or eye contact may cause inflammation and skin rashes,
changes in skin coloration, and an acne-like condition at hair follicles and skin pores.
Asphalt fumes are created when asphalt is heated. Fumes contain very small, solid, airborne particles which
are easily inhaled by the worker. Inhalation of asphalt fumes can cause irritation to the nose, throat, and
lungs. Fumes may also contain hydrogen sulfide vapors, which are very toxic, as well as the vapors
generated by the solvents used to "cut" the asphalt. (See below).
Exposure to sunlight or other ultraviolet light (such as welding) may make these skin conditions worse.
- Chronic (long term) Health Effects: Asphalt cement also causes rashes and other skin
conditions, possibly including skin cancers. In addition, asphalt particles left on the hands may
accidentally get into the eyes causing severe irritation to the eyes. Hot asphalt may also cause severe
burns if splashed onto exposed skin.
ASPHALT EXPOSURE LIMITS
- OSHA (the Occupational Safety and Health Administration) has not adopted a standard for worker
exposure to asphalt fumes despite the fact that the NIOSH recommendation was made in 1977.
- The National Institute for Occupational Safety and Health (NIOSH) has recommended that the
Short Term Exposure Limit (STEL) for exposure to asphalt fumes should be set at 5 milligrams per cubic
meter of air (mg/m3) measured during any 15 minute period.
- The American Conference of Governmental Hygienists' (ACGIH) standard (Threshold Limit Value,
or TLV) is 5 milligrams per cubic meter of air (mg/m3) averaged over eight hours.
HEALTH HAZARDS OF SOLVENT VAPORS
Vapors from solvents that are used to "cut" asphalt can also present serious health hazards. The solvent
vapors generated by heating asphalt are often more toxic than the asphalt fumes themselves. Solvents will
evaporate out of the mix at a wide range of temperatures. Heating of the asphalt mix speeds up the evaporation
process. The faster the solvent evaporates, the easier it is to inhale.
In order to understand the hazards of asphalt, it is necessary to know what solvent is used in the mixture,
how fast the substance evaporates, and how toxic the substance is.
The boiling point of a chemical determines how fast the substance evaporates. The lower the boiling
point, the easier it evaporates and the easier it is to inhale. The toxicity of a substance refers to
the effects of that substance on the human body. As indicated above, various organizations — OSHA, NIOSH and
ACGIH — recommend exposure limits for chemicals. OSHA's standards are called PELs (Permissible Exposure
Limits). OSHA's PELs are enforceable by law in states where public employees arc covered by OSHA or by
0SHA-approved state plans. (Some state plans may have PELs which are more stringent than federal OSHA's
ACGIH calls its limits TLVs (Threshold Limit Values.) TLVs are only recommended, not required.
In theory, a highly toxic chemical will have a very low PEL. In rcality, however, many PELS are outdated and
do not take into account new studies about health effects. Others are only based on a chemical's irritant
properties, instead of its ability to cause cancer or other serious health effects. It is important to remember
that a variety of sources must be checked to determine the toxicity of a chemical and discover the safest
exposure limit. Remember, legal does not mean safe.
The names of the asphalt-cutting solvents, their boiling points, and any exposure limits should be listed on
the Material Safety Data Sheet. Listed below are three solvents commonly used in asphalts, their boiling
points, health effects and exposure limits.
- Benzene (BP 176°F) is known to cause leukemia, a cancer of the white blood cells, and a serious
blood disorder called aplastic anemia which can lead to leukemia. Benzene has also been shown to cause
skin cancer in animal studies. The OSHA PEL has recently been changed to 1 part benzene per million
parts air (ppm) with a 5 ppm STEL. This means that exposures must average 1 ppm over an eight hour day,
but cannot average more than 5 ppm over any 15 minute period. The ACGIH TLV is still 10 ppm.
- Dioxane (BP 214°F) is very toxic to the liver and kidneys and has been shown to cause cancer in
laboratory testing. OSHA PEL: 25 ppm, averaged over 8 hours; ACGIH TLV: 25 ppm.
- Toluene (BP 231°F) may cause kidney and liver damage in high concentrations, as well as a skin
condition called dermatitis. It is safer to use than benzene. OSHA PEL: 100 ppm (averaged over an eight
hour day), STEL: 150 ppm for 15 minutes. This means that the average exposure over an eight-hour work
day cannot exceed 100 ppm and cannot average more than 150 ppm over any 15 minute period. ACGIH TLV:
100 ppm. STEL: 150 ppm.
Again, in order to understand the health effects of asphalt, it is important to find what solvent was used
to "cut" the asphalt mix. Remember that an "RC" mix contains the most dangerous solvents; an "MC" is less
dangerous, and an "SC" is the least dangerous of the asphalt mixes. All required and recommended exposure
limits (OSHA, NIOSH and ACGIH) should be checked. Remember, the legal limit (OSHA PEL) is not necessarily the
SAFE WORK PROCEDURES
1. Training. All workers exposed to asphalt fumes should be trained about hazards
and safe work procedures. This training should include specific information about the solvents used in
mixing the asphalt.
2. Material Safety Data Sheets (MSDSs) should be made available to each employee
assigned to work with or near asphalt processes. The MSDS should include specific information on the
solvents present in the asphalt mix and should list all pertinent information including flashpoint, boiling
point, acute and chronic effects of all chemical ingredients in the solution, protective equipment, as well
as other fire and emergency cleanup information.
3. Engineering Controls
- Substitution. The best method of controlling exposure to asphalt fumes and solvent vapors
is to substitute a safer asphalt mix. If explosion hazards are a problem in a paving operation, MC-250
may be substituted for RC-250. The flashpoint of the mix is nearly doubled, which means that the mix is
less likely to ignite.
If the toxicity of the chemical is a problem, the employer may be able to order an asphalt mixture
which contains a less toxic solvent (eg. toluene for benzene).
Finally, if a less toxic solvent cannot be substituted in the mix, a less volatile solvent may be. Less
volatile means that the boiling point of the new solvent will be higher, so less will get into the air
to be inhaled.
- Enclosure. Enclosing the process where the asphalt is used is not possible in road paving
and roofing operations. It may, however, be possible for smaller operations such as pipe covering
- Mechanization and Automation. Certain parts of asphalt processes may be mechanized. For
example, stirring asphalt in a tar kettle exposes the worker to asphalt fumes, solvent vapors, and
potentially severe burns; mechanical devices can accomplish this task without exposing the employee to
- Local Exhaust Ventilation. Local exhaust ventilation may be an effective way to control
worker exposure to fumes and vapors, particularly in areas where enclosure of the operation is
- General Dilution Ventilation. General dilution ventilation involves flooding a work area
with uncontaminated air in an attempt to remove contaminants from the worker's breathing zone. The use
of fans and blowers set up for this purpose, however, is often not adequate to remove the contaminants.
This is generally not the most effective way of removing contaminants from the worker's breathing zone,
but may be used to supplement local exhaust ventilation.
4. Respiratory Protection. While engineering controls are the preferred method for
controlling worker exposure to fumes and vapors, respirators should be worn where this is not possible. In
selecting the proper respirator, it is important to know all of the hazards to which workers may be
exposed. A NIOSH-approved dust respirator will control exposure to asphalt fumes, but will do nothing to
protect the worker against exposure to the toxic vapors given off by the solvent in the mix. In situations
where vapors are concerned, the minimum requirement would be for a full-face mask respirator with organic
vapor and particulate cartridges. Because of the possibility of eye irritation a half-face mask respirator
would be inadequate.
Improper use of respirators is dangerous. The employer must have a written
respirator program that takes into account workplace conditions, requirements for worker training,
respirator fit testing, and medical exams, as described in OSHA standard 29 CFR 1910.134 (see the AFSCME Respirators Fact Sheet).
5. Protective Clothing. Protective clothing is necessary to protect workers from
asphalt burns and irritation. In addition, many of the solvents used to cut asphalt are readily absorbed
through unprotected skin into the bloodstream, where they can travel throughout the body and cause damage
to many different organs.
NIOSH recommends thermally-insulated gloves when working with hot asphalt, long sleeve shirts, long
cuffless trousers, and metal-toed safety shoes. Clothing should be loose-fitting, collars should be closed,
and sleeves rolled down. Safety shoes should be at least 15 centimeters (cm) high and should be laced so
that no openings are left through which hot asphalt may reach the skin.
6. Face and Eye Protection. Face and eye protection are also recommended whenever
hot asphalt is used. A face shield (8" minimum) should be worn when handling heated asphalt if a full face
respirator is not worn. When liquid asphalt is hand sprayed on road surfaces as "tack coat" or "prime
coat," spraying equipment with flexible hoses and a long handle should be used.
7. Barrier Creams and Lotions. When applied to the skin, barrier creams and lotions
leave a thin film, which acts as a barrier against skin irritants. They should not be substituted for
protective clothing but may be useful along with other protective measures.
8. Fire and Explosion Hazards
- The solvents which make an asphalt an RC, MC, or SC mixture will determine the flammability limits
of the mixture. For example, RC-250, with a flashpoint near 80°F will generate flammable vapors at a
much lower temperature than will MC-3000. Extreme caution must be exercised when heating RC mixes.
Smoking, lighted matches, torches, and other possible ignition sources must be kept away from areas
where vapors are being produced.
- Welding and brazing on tar-kettles, tanks, or other vessels which either contain or have contained
asphalt is dangerous. Only qualified personnel should do such welding. The
welder must be familiar with safe procedures for welding tanks which have contained flammable
For more information about protecting workers from workplace hazards, contact the AFSCME Health and
Safety Program at (202) 429-1228, or 1625 L Street, N.W., Washington, DC 20036