Inorganic Fibrous Materials Research Articles

Exposure to MMVF in residential and commercial buildings: A literature review and quantitative synthesis.

Man-made vitreous fibers (MMVF) are a class of inorganic fibrous materials that include glass and mineral wools, continuous glass filaments, and refractory ceramic fibers valued for their insulative properties in high temperature applications. Potential health effects from occupational exposure to MMVF have been investigated since the 1970s, with focus on incidence of respiratory tract cancer among MMVF-exposed production workers. The general population may experience exposure to MMVF in residential and/or commercial buildings due to deterioration, construction, or other disruption of materials containing these fibers. Numerous studies have characterized potential exposures that may occur during material disruption or installation; however, fewer have aimed to measure background MMVF concentrations in residential and commercial spaces (i.e., non-production settings) to which the general population may be exposed. In this study, we reviewed and synthesized peer-reviewed studies that evaluated respirable MMVF exposure levels in non-production, indoor environments. Among studies that analyzed airborne respirable MMVF concentrations, 110-fold and 1.5-fold differences in estimated concentrations were observed for those studies utilizing phase contrast optical microscopy (PCOM) versus transmission electron microscopy (TEM) and scanning electron microscopy (SEM), respectively. A positive correlation was observed between respirable air concentrations of MMVF and total surface concentrations of MMVF in seldom-cleaned areas. Ultimately, available evidence suggests that both ambient air and surface concentrations of MMVF in indoor environments are consistently lower than exposure limits developed to prevent negative health outcomes among sensitive populations.

The impact of aging and environmental conditions on the effective thermal conductivity of several foam materials

The thermal conductivity, a fundamental property for insulating materials, is often advertised using a single value implied to be constant. However, research shows that the effective thermal conductivity changes as a result of material aging and the environmental parameters, including temperature and moisture content levels. In recent years, linear temperature-dependent laws have been occasionally proposed for inorganic fibrous materials, although there is increasing awareness of the fact that foam insulating materials have less regular temperature-dependent behaviours. This depends on the fact that the equilibrium among the different gasses in the material changes over time. In this paper, several polyurethane and polyisocyanurate foams are analysed in order to determine how the effective thermal conductivity is altered after accelerated aging obtained by exposing them to high temperature, high relative humidity levels, and freeze-thaw cycling. For each material, and after each aging exposure condition, measurements of the thermal conductivity were collected over a large temperature range from −20 °C to +40 °C using a Heat Flux Meter. These experimental results allow to build 3-D plots showing the effective thermal conductivity as a function of temperature and moisture content for both pristine and aged materials. Then, the measured results are used in hygrothermal simulations performed inputting the measured temperature- and moisture-dependent thermal conductivity in order to determine the effective performance of the considered insulating materials in both pristine and aged conditions. Results show that the aging of the foams and the operating temperatures have higher impacts on the insulating performance of polyisocyanurates than on polyurethanes. Additionally, high moisture levels contribute to lower performance in all foam materials, with open cell foams experiencing the greatest thermal resistance reduction. The increase in the energy fluxes across the insulating layer with respect to the constant thermal conductivity assumption was significantly higher once the effective thermal conductivity of aged materials was considered, especially when polyisocyanurate foams were modelled in cold and humid conditions.

The impact of temperature dependency of the building insulation thermal conductivity in the Canadian climate

Constant conductivity values of insulating materials are typically used in building design and assessment. However, the thermal conductivity of insulating materials depends on several factors, including the operative temperature. Linear temperature-dependent laws exist for many inorganic fibrous materials that exhibit a decreased thermal conductivity at lower temperatures. However, some insulating materials, especially the petrochemical-foamed insulations such as the polyisocyanurate, exhibit less regular behavior with poorer performance at cold temperatures. This paper investigates the impact of the thermal conductivity changes due to the temperature when the insulation is used for exterior walls and flat roofs in a cold climate. Experimental results for different materials are used in building simulations focusing on both wall and roof timber frame constructions.

The impact of the temperature dependent thermal conductivity of insulating materials on the effective building envelope performance

Constant thermal conductivity values of insulating materials are typically used in building design and assessment. However, the thermal conductivity depends on many factors, such as on the temperature and moisture content. Linear temperature-dependent laws have been occasionally proposed for inorganic fibrous materials such as fiberglass or rock wool that exhibit a decreased thermal conductivity (better performance) at low temperatures. However, the petrochemical-foamed insulating materials such as the polyisocyanurate, have less regular temperature dependent behaviors with a poorer performance at both extremely cold and warm temperatures. This means that the use of constant thermal conductivity values results in actual building envelope performance different from the design predictions, with increasing building energy consumptions, greater risks of condensation issues, and decreased occupants’ comfort. This paper aims to quantify the impact of the temperature dependency of the thermal conductivity in exterior walls and flat roofs. Experimental results over a large temperature range (from −20°C to +60°C) for different insulating materials were used in hygrothermal simulations in both continental and humid temperate climates. Common insulating materials were taken into accounts, such as fiberglass, rock wool, polyisocyanurate, and extruded polystyrene. The increase in the energy fluxes from common building envelopes once the effective thermal conductivity was considered resulted below 10% for walls and as high as 70% for roofs, especially in the cold weather. Finally, a hybrid insulation system constituted by two layers of different materials, i.e. a polyisocyanurate and a rock wool is investigated.

Environmental performance evaluation of thermal insulation materials and its impact on the building

The purpose of this paper is to examine the building's environmental performance through the insulation's material selection. Contemporary insulation materials achieve thermal conductivity values of less than 0.04 W/mK, whilst a plethora of materials, which fulfil specific requirements like mechanical and physical features according to the object specific specifications, can be found in the market. Still, the latter is dominated by inorganic fibrous materials and organic foamy ones, which were the subject of this study. The two materials’ production process was registered and evaluated based on environmental criteria with Life Cycle Analysis’ implementation, which was supported by the GEMIS model. The results obtained were used to set operating performance indicators and environmental condition indicators based on the ISO 14031 standard and accomplish the Environmental Performance Evaluation for the two materials. Moreover, insulation materials’ life cycle correlation to building's life cycle examined and expressed with energy consumption indicators.

State of the art in thermal insulation materials and aims for future developments

Insulation materials are the key tool in designing and constructing a energy thrifty buildings. This is demonstrated by the increasing thicknesses used in buildings, which also reflects in the growing sales of the branch. The European market of insulation materials is characterised by the domination of two groups of products inorganic fibrous materials and organic foamy materials. They all feature similar performance in terms of insulating capabilities, but otherwise present significant differences. These are discussed in detail in the following paper. Despite the fact that the thermal properties of the materials has not improved significantly of the last decade, a series of other features, like reaction to fire and moisture or mechanical properties have improved, sometimes even at the cost of insulation abilities. Furthermore, environmental and public health aspects play an increasing role, both in the search for ‘optimum’ materials for given applications, and in the aims set by the industry for future developments. These aims, examined within the legislative and market framework, are discussed in this paper, both as criteria for evaluating state of the art materials and as goals for future research developments.

Review : Mineral Fibres and Health

The use of inorganic fibrous materials is a comparatively new phenomenon and was uncommon before the Indus trial Revolution. Humans evolved in a comparatively fibre-free environment and consequently never fully de veloped the defence mechanisms needed to deal with the consequences of inhaling fibres. However, the urban environment now has an airborne fibre concentration of around 1 f.I -1, which is a tenfold increase on the natural background. Any sample of ambient air collected in doors or outdoors will probably contain some mineral fibres, but there is little evidence that these pose any risk to human health. They come from asbestos used in brakes, glass and mineral wools used as insulation and fire proofing of buildings, gypsum from plaster and a variety of types from many sources. Few of these have the potential to do any harm. Asbestos is the only fibre of note but urban levels are insignificant compared to occu pational exposures. When the health of cohorts occupa tionally exposed to the several types of asbestos is stud ied the problem can be put into perspective. Studies of workers in the chrysotile industry exposed to much high er dust levels than in a factory today show no excess lung cancer or mesothelioma. By comparison those liv ing near crocidolite mines, let alone working in them, may develop asbestos-related disease. As always, dose is the critical factor. Chrysotile is cleared from the lungs very efficiently, only the amphiboles are well retained. The only real health problem comes from the earlier use of asbestos products that may now be old, friable and damaged and made from amphibole or mixed fibre. If, though, these are still in good condition, they do not pose a health problem. Asbestos-related diseases are very rare in those not occupationally exposed. Where they exist exposure has nearly always been to croci dolite.

Synthetic Vitreous Fibers: A Review of Toxicology Research and Its Impact on Hazard Classification

Because the inhalation of asbestos, a naturally occurring, inorganic fibrous material, is associated with lung fibrosis and thoracic cancers, concerns have been raised about the possible health effects of synthetic vitreous fibers (SVFs). SVFs include a very broad variety of inorganic fibrous materials with an amorphous molecular structure. Traditionally, SVFs have been divided into three subcategories based on composition: fiberglass, mineral wool (rock, stone, and slag wools), and refractory ceramic fiber. For more than 50 years, the toxicologic potential of SVFs has been researched extensively using human epidemiology and a variety of laboratory studies. Here we review the research and its impact on hazard classification and regulation of SVFs.Large, ongoing epidemiology studies of SVF manufacturing workers have provided very little evidence of harmful effects in humans. Several decades of research using rodents exposed by inhalation have confirmed that SVF pulmonary effects are determined by the “Three D's”, fiber dose (lung), dimension, and durability. Lung dose over time is determined by fiber deposition and biopersistence in the lung. Deposition is inversely related to fiber diameter. Biopersistence is directly related to fiber length and inversely related to fiber dissolution and fragmentation rates. Inhaled short fibers are cleared from the lung relatively quickly by mobile phagocytic cells, but long fibers persist until they dissolve or fragment. In contrast to asbestos, most of the SVFs tested in rodent inhalation studies cleared rapidly from the lung (were nonbiopersistent) and were innocuous. However, several relativley biopersistent SVFs induced chronic inflammation, lung scarring (fibrosis), and thoracic neoplasms. Thus, biopersistence of fibers is now generally recognized as a key determinant of the toxicologic potential of SVFs. In vitro dissolution of fibers in simulated extracellular fluid correlates fairly well with fiber biopersistence in the lung and pulmonary toxicity, but several exceptions suggest that biopersistence involves more than dissolution rate.Research demonstrating the relationship between biopersistence and SVF toxicity has provided a scientific basis for hazard classification and regulation of SVFs. For a nonhazardous classification, legislation recently passed by the European Union requires a respirable insulation wool to have a low lung-biopersistence or be noncarcinogenic in laboratory rats. U.S. fiberglass and mineral wool industries and the Occupational Health and Safety Administration (OSHA) have formed a voluntary Health and Safety Partnership Program (HSPP) that include: a voluntary permissible exposure level (PEL) in the workplace of 1 fiber/cc, a respiratory protection program for specified tasks, continued workplace air monitoring, and, where possible, the development of fiber formulations that do not persist in the lung. RCF manufacturers have implemented a Product Stewardship Program that includes: a recommended exposure guideline of 0.5 fibers/cc; a 5-year workplace air monitoring program; and research into the development of high-temperature-resistant, biosoluble fibers.

Potential Pulmonary Effects of Man-Made Organic Fiber (MMOF) Dusts

In the first half of the twentieth century epidemiologic evidence linked elevated incidences of pulmonary fibrosis and cancer with inhalation of chrysotile and crocidolite asbestos, a family of naturally occurring inorganic fibrous materials. As the serpentine and amphibole forms of asbestos were phased out, synthetic vitreous fibers (SVFs; fiber glass, mineral wool, and refractory fiber) became increasingly utilized, and concerns were raised that they too might cause adverse health effects. Extensive toxicological research on SVFs has demonstrated that their pulmonary effects are directly related to fiber dose in the lung over time. This is the result of deposition (thin fibers deposit in the lower lung more efficiently than thick fibers) and lung-persistence (“biopersistence” is directly related to fiber length and inversely related to dissolution and fragmentation rates). In rat inhalation studies, asbestos was determined to be 7- to 10-fold more biopersistent in the lung than SVFs. Other than its effect on biopersistence, fiber composition did not appear to play a direct role in the biological activity of SVFs. Recently, the utilization of man-made organic fibers (MMOFs) (also referred to by some as synthetic organic fibers) has increased rapidly for a variety of applications. In contrast to SVFs, research on the potential pulmonary effects of MMOFs is relatively limited, because traditionally MMOFs were manufactured in diameters too thick to be respirable (inhalable into the lower lung). However, new developments in the MMOF industry have resulted in the production of increasingly fine-diameter fibers for special applications, and certain post-manufacturing processes (e.g., chopping) generate respirable-sized MMOF dust. Until the mid-1990s, there was no consistent evidence of human health affects attributed to occupational exposure to MMOFs. Very recently, however, a unique form of interstitial lung disease has been reported in nylon flock workers in three different plants, and respirable-sized nylon shreds (including fibers) were identified in workplace air samples. Whether nylon dust or other occupational exposures are responsible for the development of lung disease in these workers remains to be determined. It is also unknown whether the biological mechanisms that determine the respirability and toxicity of SVFs apply to MMOFs. Thus, it is appropriate and timely to review the current data regarding MMOF workplace exposure and pulmonary health effects, including the database on epidemiological, exposure assessment, and toxicology studies.