Decontamination

Decontamination is the process of clearing or neutralising various contaminants that a person or an equipment might have collected in a hazardous occupational site. The process of decontamination assures a protection from contaminants that may permeate and contaminate an individual.

Furthermore, decontamination helps in quarantining the clean areas within a site by putting a check on the transfer of contaminants through contaminant carrying personnel. It also prevents the mixing of incompatible chemicals while stopping the transfer of uncontrolled contaminants within the site.

A brief overview of the various types of contaminants that may potentially be encountered by the workers within an occupational site is introduced in this chapter. This chapter also deals with the factors influencing the communication of the contaminants and the remedies to the contamination due to these contaminants.

Adding to this, this chapter also gives out a set of general guidelines for the development of a decontamination program within a site. It also helps in deciding the health and safety aspects of the decontamination procedure.

However, decontamination for personnel or equipment contaminated by radiation is beyond the scope of this chapter. It is strongly recommended to consult a health physicist in case of contamination due to radiation occurs.

Plan for Decontamination

As part of the Site Safety Plan, a documentation plan must be developed for decontamination. This plan should be set up prior to the entrance of any personnel or equipment into the areas where there is a potential danger of exposure to certain contaminants. The decontamination plan must consider the following −

Calculate the number of decontamination stations.
Acknowledge the necessary equipment for decontamination.
Identify the various decontamination methods.
Layout plans for the prevention of clean areas from getting contaminated.
Plan procedures and steps for isolation while disposing of contaminated equipment.
Establishment plans for eliminating worker contact from the Personal Protective Equipment while decontaminating them.

In case the type of the Personal Protective Clothing/Equipment is changed, there is a change in the site conditions, or if the nature of the job within the site is changed, a revision of the plan must be conducted.

Preventing Contamination

The establishment of Standard Operating Procedures is the first step towards decontamination. These procedures minimize the contact with the contaminants, thus, minimizing the risk of contamination. Let us now consider the different activities that can help prevent contamination

Give proper emphasis on minimizing contact with hazardous substances or chemicals.
Implement remote handling, container opening, and sampling.
Put sampling and monitoring equipment in bags leaving small openings near the sensors.
Whenever possible, wear disposable outer clothing and utilize the disposable equipment.
Use removable coating for covering tools and equipment, thus, decontamination would just be one strip away.
Cover the contaminant source.

Adding to the above, Standard Operating Procedures must be established for maximising workers’ protection. For example, defined dressing procedures before entering into the hazardous site will diminish the risk of contaminants bypassing the protective clothing and thus, will significantly decrease their escape from the decontamination process.

Generally, fasteners such as buttons and zippers must be closed, along with gloves and boots being tucked, under the sleeves and the legs of the outer garments. Hoods, on the other hand, must be worn outside the collar. A secondary pair of robust outer gloves is also a must-have. Above all, proper taping of the junctures must be done to achieve the perfect prevention from contaminants.

Before using each time, the Personal Protective Equipment must be examined for any punctures and defects that might render the wearer exposed to certain contaminants. Likewise, any cut or injury on the surface of the skin also inclines the risk of contamination for the worker. Therefore, workers having wounds spread across a larger surface area on their skin must refrain from entering potentially contaminated sites.

A basic training covering all the standard operating procedures must be given to every person for avoiding contact and maximizing the safety of the workers. These procedures must be enforced throughout the entirety of the site operation.

Types of Contamination

Contaminants may either be found on the surface of the personal protective equipment or may permeate into the personal protective equipment. It is easy to remove surface contaminants; however, it is tough to remove and even detect the contaminants that permeate within the personal protective equipment.

If the process of decontamination does not remove the contaminants that have permeated into the personal protective equipment, they might continue with permeating further into the material and might inflict an unsuspected exposure. The following five factors affect the extent of permeation.

Contact time

The time for which a contaminant is in contact is directly proportional to the risk and the extent of the permeation. This is why it is very important to remove contaminants by implementing a decontamination process.

The concentration of the Contaminant

Molecules are transmitted from the areas having higher concentrations of molecules towards the areas having lower concentrations of molecules. As the concentration of the contaminant increases, its potential of getting into the clothing also increases.

Temperature

The risk of an exposure to a contaminant is directly proportional to the temperature.

Size of the molecules of the contaminant

Permeation is inversely proportional to the size of the contaminant molecules.

The physical state of the contaminants

Gases, vapors, and liquids having low viscosity, are more effective contaminants than high viscosity fluids and solids.

Decontamination Methods

Decontamination must be performed on all the clothing, equipment, samples, and personnel leaving the potentially contaminated area in the site. These areas are often referred to as Exclusion Zones. The following three approaches are usually considered for decontamination

Removing contaminants physically.
Sterilizing contaminants by using chemical detoxification.
Removing contaminants by a combination of both.

Removing contaminants physically

In most of the cases, the total mass of contaminants can be removed by implementing the following physical measures −

Rinsing
Dislodging/displacement
Evaporation
Wiping

The physical methods that deal with a high amount of pressure and/or temperature must be used with a lot of caution and should only be used where they are really necessary. The following categories of contaminants can be removed by physical means −

Loose Contaminants

Dust particles and vapours that stick to the equipment and the workers, or that are trapped in minute openings like stitches, can be removed by immersing them in water and other rinsing liquids. Antistatic solutions can be coated on the clothing to enhance the removal of electrostatic contaminants.

Adhesive Contaminants

Some contaminants stick to the clothing due to their adhesive property. A great variety of adhesive qualities can be seen across a series of contaminants. The adhesive property of these contaminants also changes depending on environmental factors such as temperature, atmospheric pressure and air density.

Some examples of these contaminants are cement, glues, resins, and muds. These contaminants have a higher adhesive property than that of elemental mercury and thus, are very tough to remove by physical means. However, these contaminants can be removed by methods such as solidification, freezing, absorption, adsorption and melting.

Volatile liquids

The process of evaporation and rinsing with water can remove the contaminants that take the form of volatile liquids. Steam jets can immensely escalate the process of evaporation of volatile liquids. However, there is a very high risk for the workers to inhale the contaminant-filled vapours. Therefore, proper caution must be taken to ensure proper isolation of the vapours.

Removing Contaminants Chemically

Washing and cleaning with cleaning solutions is the next step that should be followed after the physical removal of contaminants. The following methods can be utilized to do this −

Dissolving Contaminants

Surface contaminants can be chemically removed by dissolving these contaminants in a solvent. Chemical compatibility of the solvents with the contaminants is essential for the removal of these contaminants. To be specific, this is particularly important in the case of decontaminating Personal Protective Clothing that is made up of organic materials and can be damaged by organic solvents.

Adding to this, a very high degree of caution must be taken in the selection, usage and the disposal of highly flammable and potentially toxic organic solvents. The following kinds of organic solvents are the most widely used −

Ethers
Alcohols
Ketones
Straight-chain Alkenes
Petroleum products
Aromatics

Halogenated Solvents

Generally, halogenated solvents are toxic in nature and are not compatible with Personal Protective Clothing. These solvents must only be used in extreme cases, where it is impossible for other cleaning agents to remove the contaminants.

Surfactants

Physical cleaning methods are aided by surfactants by the reduction of adhesive forces between the contaminants and the surface to be decontaminated. The most commonly used surfactants are household detergents. Detergent, when mixed up with certain proportions of organic solvents, results in a better dispersal and dilution of contaminants.

Solidification

The physical removal of liquids or gel-based contaminants can be greatly enhanced by solidifying them. The following mechanisms of solidification are usually followed across industries −

Using absorbents such as powdered lime and grounded clay to remove moisture.
Using chemical reagents and polymerisation catalysts to chemically react with the contaminants.
Using ice water to freeze the contaminants.

Rinsing

The contaminants can be removed through rinsing by solubilisation, physical attraction, and dilution. Rinsing multiple times with cleaning solutions removes a lot of contaminants as compared to a single rinse. Rinsing continuously will remove even larger amounts of contaminants than multiple rinsing.

Sterilisation

A more practical approach for the inactivation of infectious agents is to chemically disinfect them. However, it is generally impractical to implement standard sterilisation techniques for bigger equipment and protective clothing. This is why sterilisation is usually recommended for disinfecting infectious agents specifically.

Designing a Decontamination Facility

In a hazardous occupational site, the Contamination Reduction Zone (CRZ) must contain the decontamination facility. The Contamination Reduction Zone is usually the area between the Support zone and the Exclusion Zone. Several factors within a site contribute to the determination of the level of decontamination required. These factors include −

The toxicological, physical, and chemical property of the contaminants.
The site’s pathogenicity.
The number of contaminants along with their location and containment.
The potential of contaminants for permeating, degrading, and penetrating the substances used for creating the personal protective clothing and equipment.
The reach of incompatible wastes.
The locomotion of the personnel and the equipment across various zones in the occupational site.
The decontamination methods available for workers.
The effect of the decontaminating substances on the safety and the health of the workers.
Emergencies.

An organised process must be laid out by decontamination procedures for reducing contamination across various levels. A series of procedures in a particular sequence must be included in the decontamination process.

For example, heavily contaminated items such as boots and gloves must be the first to be decontaminated. A separate station must be dedicated to each procedure to reduce cross contamination. Decontamination line is the term given to the sequence of stations. Furthermore, physical barriers must be present in between these stations for preventing cross-contamination.

The entry and exit points of different zones must be legibly marked and there must be separate entry and exit points for the Contamination Reduction Zones and the Exclusion Zones. Separate dressing and redressing stations must be provided at the entrance and the exit points of the Contamination Reduction Zones.

Methods of Disposal

It is very crucial to decontaminate and dispose the equipment and materials used for decontamination. The collection and placement of brushes, buckets, clothing, and other tools must be done within containers that are properly labelled. Moreover, the washed water and the solutions used in the decontamination process must be collected and isolated from the environment. Plastic bags should be used to contain the clothing and the equipment that are not completely decontaminated.