**1. Introduction**

Since the late 19th century, hydrogen peroxide (H2O2) has been used as a disinfectant and antiseptic due to its potent antimicrobial properties against a wide range of pathogens [1]. Hydrogen peroxide attacks the essential external structures of pathogens (i.e. cell walls, viral envelopes, etc.) via a simple oxidation reaction, thereby weakening the pathogen's physical structure until it ultimately lyses from its own osmotic pressure [2–4]. Most commonly, H2O2 is used as a liquid antiseptic and disinfectant, but solutions of H2O2 are also vaporized and dispersed as a method of disinfection of indoor spaces. This process, however, requires the complete evacuation of personnel from the treated spaces, both during and for some time after the treatment, to protect human occupants from the toxic effects of the highly concentrated droplets [5, 6]. Symptoms of overexposure to H2O2 include irritation of the eyes, nose, throat, skin, and/or lungs, and concentrations over 75 parts per million (ppm) are considered "immediately dangerous to life or health" in humans [7, 8]. Droplets of vaporized hydrogen peroxide, depending on the generator, may contain concentrations

of approximately 400 ppm [9], therefore, while vaporized hydrogen peroxide is extremely effective as a sterilant, its potential for use in continuously occupied spaces is limited by its potency and potential toxicity to human occupants [10, 11].

Hydrogen peroxide is also an essential component of the human respiratory system, with human lungs maintaining an equilibrium concentration between 10−6 and 10−4 M via the lactoperoxidase system of enzymes [12]. Two enzymes within this system, known as the Duox compound, constantly produce hydrogen peroxide, while the third enzyme, lactoperoxidase, converts that hydrogen peroxide into an even stronger oxidizing agent, the hypothiocyanite ion (OSCN<sup>−</sup> ) [12, 13]. This enzymatic system allows the human body to tolerate low levels of hydrogen peroxide exposure without experiencing irritation or damage.

Recently, a new method of hydrogen peroxide generation and delivery termed Dry Hydrogen Peroxide (DHP™) was developed, with the goal of enabling safe continuous microbial inactivation to occur in occupied indoor spaces either when installed within an existing HVAC system or as a stand-alone device (**Figures 1** and **2**) [14]. DHP is produced by devices that include a 363 nm wavelength ultraviolet A (UV-A) bulb, which activates a proprietary photocatalyst that has been applied to a two-dimensional framed polyester mesh, referred to as a "sail". Photons of UV-A radiation from the bulb excite electrons in the catalyst, promoting them to a higher energy state. This creates a positively charged "electron hole" in the valence band in the catalyst atoms, creating an active site. When ambient humidity (H2O) is adsorbed into these active sites, an electron is scavenged from the water molecule. This causes a subsequent release of a proton (H+ ) by the water molecule, and the resulting structure is a hydroxyl radical (OH˙). The catalyst now has a free electron, a proton (H+ ), and a hydroxyl radical available to perform oxidation reactions. Under normal circumstances, these three components simply combine to produce a water molecule in the gas phase. DHP technology, however, uses a proprietary plasma separation process to isolate hydroxyl radicals from the subatomic particles. This separation of the plasma allows for the hydroxyl radicals to combine and form stable molecules of hydrogen peroxide in a pure gas state (DHP), which are then dispersed throughout the space being treated. The subatomic particles that remain on the catalyst are then scavenged by ambient diatomic oxygen (O2), forming more molecules of DHP by means of reduction. The concentrations of DHP that are produced through this process are well below the OSHA safety limit of 1 ppm, allowing the lactoperoxidase system to easily maintain the equilibrium concentration of hydrogen peroxide to the level naturally present in the lungs [12, 13]. Additionally,

**Figure 1.** *In-line Dry Hydrogen peroxide (DHP) device intended for use in an HVAC system.*

*Dry Hydrogen Peroxide for Viral Inactivation DOI: http://dx.doi.org/10.5772/intechopen.100451*

**Figure 2.** *Stand-alone Dry Hydrogen Peroxide (DHP) device.*

it has been confirmed that DHP devices produced by the patent holder do not produce ozone, according to Underwriter's Laboratories (UL) Standards 867 and 2998 [15, 16]. A recent study performed by Ramirez et al. reported no incidence of symptoms associated with hydrogen peroxide overexposure in pediatric oncology patients who were continuously exposed to DHP during their stay in a Pediatric Intensive Care Unit (PICU) [17].

Due to the novelty and mechanism of generation of DHP, this disinfection system is often confused with older technologies, such as vaporized hydrogen peroxide, bipolar ionization, and photocatalytic oxidation, though it is distinct from each of those technologies.
