This is a First Look at a column to appear in the September 2019 issue of
Water Well Journal
Decontaminating clothing and equipment is a must after work on some jobsites.
By Alexandra Walsh
Removing or neutralizing contaminants that have accumulated on materials worn by workers and equipment is critical to health and safety at water well drilling sites where workers might be exposed to hazardous waste or other substances.
Decontamination protects workers from hazardous substances that may contaminate and eventually permeate protective clothing, respiratory equipment, tools, vehicles, and other equipment used on jobsites.
Decontamination protects all personnel at the site by minimizing harmful materials being transferred into clean areas and helps prevent mixing incompatible chemicals.
Finally, the decontamination process protects the community at large by preventing uncontrolled transport of contaminants from the drilling site.
Planning for Decontamination
A decontamination plan should be developed as part of the site safety plan and set up before any personnel or equipment enter areas where any potential for exposure to hazardous substances exists. The decontamination plan should:
- Determine the number and layout of decontamination stations
- Determine the decontamination equipment needed
- Determine appropriate decontamination methods
- Establish procedures to prevent contamination of clean areas
- Establish methods and procedures to minimize workers contacting contaminants while removing personal protective clothing and on equipment
- Establish methods for disposing of clothing and equipment that are not completely decontaminated.
The decontamination plan should be revised whenever the type of personal protective clothing or equipment changes, conditions at the site change, or hazards at the site are reassessed based on new information.
Prevention of Contamination
The first step in decontamination is to establish standard operating procedures (SOPs) that minimize contact with waste and thus the potential for contamination.
Here are some examples:
- Stress work practices that minimize contact with hazardous substances (don’t walk through areas of obvious contamination; don’t directly touch potentially hazardous substances).
- Use remote sampling, handling, and container-opening techniques (drum grapplers, pneumatic impact wrenches).
- Protect monitoring and sampling instruments by bagging (make openings in the bags for sample ports and sensors that must contact site materials).
- Wear disposable outer garments and use disposable equipment where appropriate.
- Cover equipment and tools with a strippable coating that can be removed during decontamination.
- Encase the source of contaminants with plastic sheeting or overpacks.
In addition, SOPs should be established that maximize worker protection. For example, proper procedures for dressing prior to entering the contaminated area (generally referred to as the exclusion zone) will minimize the potential for contaminants bypassing the protective clothing and escaping decontamination.
In general, all fasteners should be used (zippers fully closed, all buttons used, all snaps closed). Gloves and boots should be tucked in under the sleeves and legs of outer clothing, and hoods (if not attached) should be worn outside the collar.
Another pair of tough outer gloves is often worn over the sleeves. All areas where clothing connects with the body should be taped to prevent contaminants from running inside the gloves, boots, jackets, or one-piece suits.
Prior to each use, the personal protective equipment should be checked to make sure it contains no cuts or punctures that could expose workers to wastes.
Similarly, any cuts and scratches to the skin surface may enhance the potential for chemicals or infectious agents that directly contact the worker’s skin to penetrate into their body. Particular care should be taken to protect these areas. Workers with large areas of damaged skin should be kept from working onsite until their skin heals.
All personnel should be trained in the SOPs for minimizing contact and maximizing worker protection—and these procedures should be enforced throughout operations at the site.
Types of Contamination
Contaminants can be located on the surface of personal protective equipment or permeated into its material. Contaminants on the surface can be easy to detect and remove, but contaminants that have permeated a material are often difficult or almost impossible to detect, let alone remove.
Five major factors affect the extent of permeation:
- Time. The longer amount of time a contaminant is in contact with an object, the greater the probability and extent of permeating. For
this reason, minimizing contact time is one of the most important objectives of a decontamination program.
- Concentration. Molecules flow from areas of high concentration to areas of low concentration. As concentrations of wastes increase,
the potential for permeating personal protective clothing increases.
- Temperature. An increase in temperature generally increases the permeation rate of contaminants.
- Size. Permeation increases as the size of the contaminant molecule becomes smaller, and the size of the pore space in the material being permeated becomes larger.
- Speed. Gases, vapors, and low-viscosity liquids as a rule tend to permeate more readily than high-viscosity liquids or solids.
Methods of Decontamination
Decontamination methods either (1) physically remove contaminants, (2) inactivate contaminants by chemical detoxification or disinfection/sterilization, or (3) remove contaminants by a combination of both physical and chemical means.
In many cases, contamination can be removed by physical means involving dislodging/displacement, rinsing, wiping off, and evaporation.
Physical methods involving high pressure or heat should be used only as necessary and with caution since they can spread contamination and cause burns.
Contaminants that can be removed by physical means can be categorized as follows:
- Loose contaminants. Dusts and vapors that cling to equipment and workers or become trapped in small openings, such as the weave of clothing fabrics, can be removed with water or a liquid rinse. Removal of electrostatically attached materials can be enhanced by coating the clothing or equipment with anti-static solutions. These are available commercially as wash additives or anti-static sprays.
- Adhering contaminants. Some contaminants cling by forces other than electrostatic attraction. Contaminants such as glues, cements, resins, and muds have much greater adhesive properties and are difficult to remove by physical means. Physical removal for contaminants include scraping, brushing, and wiping. Removal of adhesive contaminants can be enhanced through solidifying, freezing with dry ice or ice water, adsorption or absorption using powdered lime or kitty litter, or melting.
- Volatile liquids. Volatile liquid contaminants can be removed from protective clothing or equipment by evaporation followed by a water rinse. Evaporation of volatile liquids can be enhanced by using steam jets. With any evaporation or vaporization, care must be taken to prevent workers inhaling the vaporized chemicals.
Physical removal of contaminants should be followed by a wash/rinse process using cleaning solutions. These cleaning solutions normally use one or more of the following methods:
- Chemical removal of surface contaminants can be accomplished by dissolving them in a solvent. The solvent must be chemically
compatible with the equipment being cleaned. This is particularly important when decontaminating personal protective clothing constructed of organic materials that could be damaged or dissolved by organic solvents. In addition, care must be taken in selecting, using, and disposing of any organic solvents that may be flammable or potentially toxic. Organic solvents include alcohols, ethers, ketones, aromatics, straight-chain alkanes, and common petroleum products.Halogenated solvents generally are incompatible with personal protective equipment and are toxic. They should only be used for decontamination in extreme cases where other cleaning agents will not remove the contaminant.
Because of the potential hazards, decontamination using chemicals should be done only if recommended by an industrial hygienist or other qualified health professional.
- Surfactants enhance physical cleaning by reducing adhesion forces between contaminants and the surface being cleaned, and preventing redeposit of the contaminants. Household detergents are among the most common surfactants. Some detergents can be used with organic solvents to improve the dissolving and dispersal of contaminants into the solvent.
- Turning liquid or gel contaminants into a solid can enhance their physical removal. Solidifying works by (1) removing moisture using
absorbents such as grounded clay or powdered lime; (2) chemical reactions using polymerization catalysts and chemical reagents;
and (3) freezing using ice water.
- Rinsing removes contaminants through dilution, physical attraction, and dissolving in liquid. Multiple rinses with clean solutions
remove more contaminants than a single rinse with the same volume of solution. Continuous rinsing with large volumes will remove even more contaminants than multiple rinsings with a lesser total volume.
- Chemical disinfectants are a practical means of inactivating infectious agents. Unfortunately, standard sterilization techniques are generally impractical for large equipment and for personal protective clothing equipment. For this reason, disposable PPE is recommended for use with infectious agents.
Decontamination methods vary in their effectiveness for removing different substances. The effectiveness of any decontamination method should be assessed at the beginning of a program and periodically throughout the lifetime of the program.