There is an increasing attention concerning Indoor air quality for public health because individuals spend up to 90% of their time in the indoor environment (Bluyssen, 2009). EPA studies of human exposure to air pollutants indicate that the indoor pollutant levels may be 25 times and it maybe reaches to 100 times higher than outdoor levels (Daisey et al., 2003). Volatile Organic Compounds (VOCs) are considered to be the most important indoor pollutants due to continuous emissions from many sources (Bacaloni et al., 2011). Finishing materials among all sources have a significant attention showing that more than 60% of VOCs emissions come from finishing materials and furnishings.

Numerous studies have shown that reducing the indoor air quality (IAQ) result from the VOCs emissions of from commonly used materials such as wood products, floor coverings, wall coverings, etc. These emissions may cause general symptoms from inhalation of fumes or vapors and skin absorption (Hussain et al., 2015). The symptoms include a headache; eye, nose, or throat irritations; a dry cough; dizziness and nausea; difficulty in concentration; tiredness. The health effects differ widely as shown in (Figure 1), based on the exposure period that can be either acute term exposures (hours to days) or chronic exposures (years to a lifetime) (Bluyssen, 2009).

Generally, finishing materials appear in composite forms such as the wall assembly (paint/ gypsum board) or the floor assembly (varnish/ stain/ wood). VOC emissions floor assembly has not been theoretically examined. From the experimental studies of carpet/adhesive assembly, it has been found that the main source of VOC comes from the adhesive in the floor assembly. It has been found that adhesive in the floor assembly is the main source of VOC; the emission of the assembly displays lower delayed peak and slower decay rate in comparison with the adhesive alone [(Black et al., 1991); (Low et al., 1998)]. Thus, it is more important to understand multi-layer material emission characteristics in a building than single-layer one. Some multi-layer models were proposed (Bodalal, 1999), a general multi-layer emission model that can be used to simulate wet/dry, dry/dry, dry/wet material assemblies is not yet available (Haghighat & Huang, 2003).

Until now, abundant studies have been done on of VOC emissions measurement. Most of the studies use a small-scale test chamber under controlled environmental conditions. Such these measurements are very essential in order to accumulate and compile a reliable database of indoor materials. However, there is maybe a difference between both the geometry and boundary conditions in buildings and that in the test sample. Hence, the measured data from a chamber may not be entirely suitable for actual buildings. On the other hand, with the rapid progress of computer hardware and numerical algorithms, mathematical models and numerical simulations can partly overcome the disadvantage of laboratory measurements (Xu & Zhang, 2003).

This paper discusses the simulation method of predicting VOCs emissions from a multilayer material with a specific focus on the emissions from wood-based floor material. Three types of coating layers; stain, wax, and varnish were applied to the natural type of wood flooring; unfinished hardwood- Red Oak. The objective of this study is to estimate the wood coating materials contribution to the TVOCs emissions of wood product in the indoor environment to shed light on the importance of comprehensive analysis of wood material with all treatment coatings.

Most finishing and furniture consist of multi-layer materials which are considered to be as sources of VOCs. These finishing materials may include both wet and dry materials such as carpeting, wallpaper, wood floor, paint, and glue. Indoor air quality is considerably affected by the VOCs emission from dry building materials, as not only the emission is a long-time process but their large surface areas are also permanently exposed to indoor air (Yang et al., 2001).

On the other hand, the characters of VOC emissions from wet materials have a high initial emission rate and fast decay, afterwards a low emission rate and slow decay. It can be clarified by three emission stages from wet materials: evaporation dominant phase (wet material), transition phase (relatively wet), and internal diffusion controlled phase (completely dry) (Yang et al., 2001) . For wet materials, such as glue, wood stain, VOC concentration within the materials has a very high initial, consequently (Haghighat & Huang, 2003).

Each layer in the multilayer assembly has VOCs emissions, not only from the top surface but also from the core and bottom layer. It is essential to recognize the emission characteristics of common multilayer materials to provide valuable information for the manufacturing process and to finally eliminate the VOCs released into the indoor air (Xu & Zhang, 2009). Multi-layer materials contain three composition forms: dry/dry (e.g. composite particleboard or plywood), dry/wet (e.g. vinyl floor tile+ glue+ plywood; carpet+adhesive) and wet/dry (e.g. paint + gypsum board). The material configuration and VOC emission processes are shown in (Figure 2) (Haghighat & Huang, 2003).

Most types of wood-based flooring are made of composite assembly as natural wood floor usually passes through numbers of treatment steps in the finishing process as shown in (Figure 3) (Kim, 2010). This treatment applying as a coating layer such as stain, wax, and varnish layer. Wood stains, also known as wood dyes are designed to change the color of wood while leaving the grain still visible by soaking pigment into wood fibers with a solvent and then having it set and bind to the wood. Most stains don’t offer a lot of protection to wood, so when using a stain it’s regularly a good idea to apply a protective coat of something else like a varnish or wax (Rowell, 2012).

Varnish begins as oil, but it’s cooked with a resin to produce a drying, hard, wood finish. Its main role is that of a protective coating on the surface; it doesn’t penetrate like wax does (Flexner, 1993). Waxes are derived from many types of mineral, vegetable and animal sources. As a finish, waxes don’t penetrate wood, but rather sit atop it. They will prevent it from oxidizing but don’t particularly enhance the wood. (Shupe et al., 2008). Applying all these three types of coatings aren’t be essential for each wood finishing process as each type of wood floor has its required treatment steps.

This paper established a simulation procedure to evaluate the VOC emissions for each type of flooring coating and its contribution to the TVOCs emission of the wood flooring. To simulate indoor VOC concentrations in a residential unit due to wood coating materials, some information and key parameters discussed in Eq. (1) need to be determined. The whole simulation procedure can be generally divided into three steps including:

Every step in this procedure has its tools either using the field visits to using different simulation tools. A detailed discussion of each step is given in the following case study section.

The above-proposed procedure with the three steps has been applied in a typical master bedroom from the apartment that was selected randomly from residential towers in Mansoura. Egypt using IA-QUEST simulation program.

During the emission simulation, the concentrations of TVOCs resulted from different types of wood coatings were predicted. Figures (Figure 7) show the concentration-time profiles during the 336-h test period for VOCs emitted from the eight scenarios. There are some findings as follows:

After discussing the VOCs concentration for each case resulted from different type of coating layers, there is a necessary need for analyzing the VOCs concentration along the simulation period as shown in (Table 4) to understand the VOC behavior for each coating layer. The analyses show the following:

A method to estimate the coating layers contribution to the TVOCs emissions of wood product in the indoor environment was established. This method is essential to shed light on the importance of comprehensive analysis of wood material with all treatment coatings. The method has been done using simulation tools for the typical master bedroom to investigate the influence of three wood coating materials; stain, wax, and varnish which were applied to an area of natural hardwood Oak floor.

The TVOCs emission data resulted from the different coated wood floor was compared with VOCs emissions caused by the natural wood floor to find out the coating material contribution in TVOCs emissions of wood flooring material in the interior space. The results from the comparison show that the coating layer may be considered as the main source of emissions in the multilayer wood flooring. Also, the results show varied value for VOCs concentration due to different types of coating that indicate the importance of analyzing and studying the different type before installing. For example, there is a wide range in TVOCs concentration resulted from different coating layers for the purpose of protecting and polishing; varnish layer recorded TVOCs concentration lower than using Oil-based wax while using Water-based wax is the lowest results among the polishing materials. On the other hand, there is an essential need for analyzing the long-term behavior for each type of layers to understand the VOCs emissions mechanism that differ during their decay.