A key part of any restoration project is the proper selection, handling and use of disinfecting agents.

Controlling microbial activity — and the odors, health hazards and secondary damages they can cause — is critical to successful restoration and cleaning.

In this article, we’ll discuss the two types of disinfectants. We’ll also discuss the differences between disinfectants and sterilants and conclude with a few thoughts about the significance of dwell time.


Chemists often use long names to describe molecules, so people develop nicknames for them. That's why most of you know “quaternary ammonium chloride” as simply, “quats.”

The proper name is even longer: Diisobutylphenoxyethoxy ethyl dimethyl benzyl ammonium chloride monohydrate. Some quats are used as fabric softeners and static control agents, but this article addresses quats with antimicrobial effects.

How do quats actually kill microbes? There are several theories, but two are most widely accepted:

1. Quats attack cell membranes, causing them to leak, sort of like a chemical pin bursting a germ balloon.

2. Quats disrupt enzymes that are critical to proper cell function. Using a mechanical analogy again, it's like throwing a monkey wrench into gears.

Quats are a common active to many institutional and home products, even antiseptics. Advantages include:

  • Very low odor.
  • Low toxicity compared to other actives.
  • Non-corrosive to metals and doesn't bleach textiles (in contrast to chlorine).
  • Broad efficacy (but note that  quats don't kill all germs).
  • Tolerant of a wide range pH conditions, making it versatile.
  • Can handle some organic soil load before becoming ineffective.
  • Bacteriostatic and fungistatic properties provide lasting effects that keep killing germs.

It’s good to be aware that if a product label requires re-application after a period of time, it’s likely the stasis or lasting benefits of the product are limited.

Every tool has its limitations, and quats are no different. Limitations include:

  • Soaps, and surfactants similar to soaps, can easily contaminate quats and inactivate them.
  • Hard water also inactivates quats, so they may need to be blended with a water conditioning agent.
  • Some quats are not readily biodegradable.
  • Quats must be properly diluted to maintain efficacy.

Tip: Beware of over-diluting quats. Some studies show that germs can grow in over-diluted quat solutions. Test strips are available to measure the concentration of ready-to-use quat solutions. This is a great reminder to follow label directions.


Phenol is relatively corrosive and toxic compared to quaternary compounds. Chemists have tinkered with the molecule — creating variations — to limit the molecule's dangerous properties while retaining its germ-killing characteristics. As a result, there are quite a number of phenolic-type disinfectants in the marketplace today.

The key mechanism a phenolic compound uses to kill germs is “denaturation,” which is the disruption of a protein's structure.

Germs use enzymes to digest food, grow and reproduce. Enzymes are comprised of proteins as a key part of their biochemical machinery. Denaturing a protein renders it useless to the germ, and the germ can no longer grow or reproduce or digest food. Boiling an egg denatures the egg’s proteins, rendering any germs harmless and making the egg easier for us to digest.

Advantages of phenolic disinfectants include:

  • Phenols have broad efficacy and kill a number of germs, including bacteria, virus, fungi, even tuberculosis, which is a particularly durable bacterium.
  • While phenols vary widely in toxicity, one member of this group (thymol) has such low toxicity that it is used in some brands of mouthwash.
  • Phenols tend to be more economical than many other disinfectant actives.

Some limitations of phenols include:

  • Many versions of phenols are corrosive or irritating to skin and eyes.
  • Phenols tend to have a stronger odor than other disinfectant actives.
  • Phenols are inactivated by certain detergent compounds and at certain pH levels.
  • As always, when using an EPA-registered disinfectant, be sure to follow label directions.

Today, either quats or phenols are the primary active ingredient in most antimicrobials used in the restoration and cleaning industries.

There are alternatives. Oxygen-based disinfectants are gaining some ground, and the push for green cleaning options has resulted in the introduction of a number of products that reduce environmental impact.

But for now, quats and phenols remain our most effective tools for disinfecting the restoration job site.

Disinfectants vs. sterilants

Both products kill germs and are for use on inanimate (not living) surfaces; however, the major difference between a disinfectant and a sterilant is that sterilants destroy bacterial spores as well as active, growing colonies.

Bacterial spores are very durable life forms, so it takes strong chemical action and extended contact time to destroy them. Typical sterilant actives include chemicals, such as peracetic acid, ethylene oxide (a gaseous material) and glutaraldehyde.

Making the right choice

You might ask yourself: If sterilants are so much more effective than disinfectants, why not use them in place of disinfectants?

The main reason is that sterilants have higher toxicity and are typically used in controlled conditions, such as in a medical environment.

For example, a device that penetrates the skin must be 100 percent free of microbial contamination. You don't want any bacterial spores getting into the bloodstream during an injection, because the body provides the perfect environment for bacteria to flourish: Warmth and moisture.

This is why most medical devices, such as scalpels, needles and sutures, must be sterilized prior to use. In contrast, normal environmental cleaning does not require complete elimination of bacterial spores.

Know your facts

Sometimes the term “sterilizing” is used interchangeably with “sanitizing” or “disinfecting.” You might hear someone claim that they are “sterilizing” a carpet or wall.

While you can do this in theory, it just doesn't happen in practice except in specialized industrial applications. And as you might expect, sterilants require government registration.

Dwell on it

Dwell time is one of the most important — yet most misunderstood — references found on all disinfectant labels. A dwell time is the number of minutes that an applied product must be in contact with the surface and remain wet in order to ensure compliance. On many product labels, dwell time is indicated with phrases like “must remain wet for” or “contact time.”

Most labels call for a 10 minute contact time; for a cleaner, that may seem like a long time. However, in disaster restoration applications, a 10 minute dwell time is not unreasonable and in most cases, the area being treated will easily remain wet for the required period.

Ten minutes is a standard “rule of thumb” for dwell time. Disinfectant products that indicate dwell times of less than 10 minutes are able to do so because the manufacturer has conducted additional testing to show efficacy with shorter dwell times.

Typically, however, these tests are specific to a certain organism. This feature is handy if you know that only that organism is on the surface, but if you are not sure (and you usually aren’t), use the standard dwell time of 10 minutes.

The proper selection, handling and use of disinfecting agents to controlling microbial activity — and the odors, health hazards and secondary damages they can cause — is critical to successful restoration and cleaning.

Mike Kerner has been senior scientist with Legend Brands since 2009. He has 30 years of experience related to cleaning and restoration chemistry. Kerner provides technical support for chemical products in the various Legend Brands divisions including Dri-Eaz, ProRestore and Sapphire Scientific. He recently started providing technical support for Chemspec, a Legend Brands partner company.