Frequently Asked Questions
Aerogel is a synthetically produced amorphous silica gel impregnated into a non-woven flexible fabric substrate, offering the twin benefits of extreme thermal performance and a flexible blanket form. To meet customer demands, Aspen Aerogels may use a variety of aerogel additives and fabric substrate materials.
Aspen Aerogels products utilize nanoporous structures that minimize the three mechanisms of thermal transport, resulting in thermal conductivity values in the 12 - 15 mW/m-K range.
The “nanotechnology” aspect of Aspen’s blanket products relate to the nanometer scale voids incorporated in the amorphous silica gel matrix. Thus, Aspen’s materials are considered nanotechnology from a void space, rather than overall material, basis. The void space is what gives rise to the exceptional insulation performance of our materials.
The structure of aerogel is much larger than a nanometer (10-9 meter). The pores (or air space) of the aerogel structure are on the factor of nanometers. However, it would take tremendous amounts of energy to separate the aerogel particles from their aggregated state.
No. The smallest aerogel particle size is more than seven times larger than the largest nanoparticle. This has been confirmed by an independent laboratory analysis.
The generally accepted criteria for nanoparticles are dispersible particles having two or three dimensions greater than 1 nm and less than about 100 nm. Five different aerogel dusts were tested by an independent, outside laboratory using a Malvern Mastersizer 2000 LASER diffractor. Particles less than 710 nm were not detected in any sample analyzed. Therefore, the smallest aerogel particle size detected is more than seven times larger than the largest nanoparticle.
No. Aerogel is a synthetic amorphous silica, which is distinctly different from crystalline silica. Silica is composed of one silica atom and two oxygen atoms.
The United Nation’s Organization for Economic Co-operation and Development (OECD) has been characterizing the hazardous properties of High Production Volume (HPV) chemicals. The “Screening Information Data Set” (SIDS) for synthetic amorphous silica was released in 2004. The SIDS report concluded that synthetic amorphous silica (SAS) is a low priority for further study. Excerpts from the OECD SIDS Human Health conclusions are included below:
Absorption, disposition, elimination: SAS forms [CAS No 7631-86-9] are rapidly eliminated from the lung tissue during and after prolonged inhalation exposure of experimental animals with no disproportionate disposition occurring in the mediastinal lymph nodes, whereas crystalline forms exhibit a marked tendency to accumulate and persist in the lung and lymph nodes. Intestinal absorption of SAS appears to be insignificant in animals and humans. There is evidence of ready renal elimination of bioavailable fractions.
Acute toxicity: Following inhalation exposure of rats to the highest technically feasible concentrations of 140 to ~2000 mg/m3 SAS, no lethal effects were observed. Oral and dermal administration of SAS and amorphous silicates failed to cause mortality at the highest doses tested: LD0 values ranged from 3300 to 20000 mg/kg in rats.
Irritation and Sensitization: Synthetic amorphous silica and silicates are not irritating to skin and eyes under experimental conditions, but may produce dryness following prolonged and repeated exposure. No sensitization experimental data are available on the synthetic amorphous silicas and silicates. There is long experience in humans. Data collected from industrial hygiene surveillance over the last 50 years do not indicate any potential for skin sensitization. As mentioned above, there are reports describing dryness or cutaneous irritation that may be misinterpreted as a sign of sensitization or allergy.
Medical surveillance records on workers gave no evidence of skin sensitization over decades of practical experience. Given the inherent physico-chemical properties and ubiquitous nature of this class of compounds, there is no structural alert to indicate a sensitizing potential.
The US EPA reviewed several toxicity studies for synthetic amorphous silica including four acute toxicity studies (acute oral LD50 in the rat, acute inhalation LC50 in the rat, primary eye irritation in the rabbit, and primary dermal irritation in the rabbit); four mutagenicity studies, and an oral toxicity study. The US EPA summary of these study results was as follows:
Acute toxicity studies. No mortalities were observed for the oral and inhalation studies. For the primary eye irritation study, there was no corneal opacity or iridial irritation in any of the eyes. For the dermal study, there was no dermal irritation at 72 hours. For the acute toxicity study, the oral LD50 is >5,000 milligrams/kilograms (mg/kg). For the acute inhalation study, the LC50 is >2.08 mg/L. All studies are toxicity category IV.
Mutagenic studies. In all four studies there was no indication of any mutagenic activity associated with exposure to silica, amorphous, fumed (crystalline free).
Oral toxicity of fumed silica. There were no mortalities or clinical signs. There was no significant difference between the test group and the control group with respect to silica concentration in the carcass.
Based on their analysis of the reviewed studies, the US EPA concluded the following:
“Silica, amorphous, fumed (crystalline free) has a demonstrated lack of toxicity. The acute toxicity studies are toxicity category IV. The mutagenicity studies are negative. Silica, amorphous, fumed (crystalline free) is not classifiable, as to its carcinogenicity however, given its amorphous nature, it is not expected to pose a carcinogenic risk. Silicas are considered to be inert when ingested, and due to the high molecular weight it is unlikely to be absorbed through the skin. There should be no concerns for human health, whether the exposure is acute, subchronic, or chronic by any route.”
The health effects of synthetic amorphous silica are significantly different from the health effects of crystalline silica. No evidence of silicosis has been found from epidemiological studies of workers with long-term exposure to intentionally manufactured synthetic silica4. From a health standpoint, a significant different between crystalline and amorphous silica could be lung clearance. Studies of various animal species have shown that amorphous silica products can be completely cleared from the lungs.
The International Agency for Research on Cancer (IARC) considers synthetic amorphous silica to be not classifiable as to its carcinogenicity to humans (Group 3).
- United Nations Environmental Programme (UNEP), Organization for Economic Co-operation and Development (OECD) Screening Information Data Set (SIDS) Initial Assessment Report, Synthetic Amorphous Silica, July 23, 2004.
- Federal Register, Vol. 67, No. 94, May 15, 2002, 34616-34620.
- Federal Register, Vol. 67, No. 94, May 15, 2002, 34616-34620.
- Merget, R et al, “Health hazards due to the inhalation of amorphous silica”, Arch Toxicol (2002) 75: 625-634, November 29, 2001.
- Warheit, David, “Inhaled Amorphous Silica Particulates: What Do We Know About Their Toxicological Profiles?”, Journal of Environmental Toxicology and Oncology, 20(Suppl. 1) 133-141 (2001).
Handling of aerogel blankets will produce dust. Aerogel dust exposure can produce the following effects:
- A sensation of dryness to skin
- Irritation to eyes, skin, respiratory track
These effects are not unique to aerogels, but are consistent with the handling of a host of dusty materials. When inhaled in sufficient amounts, any dust or particulate will cause respiratory effects. Excessive exposure to any type of dust can cause skin or mucous membrane irritation by chemical or mechanical action or rigorous skin cleaning.
The US OSHA standard for amorphous silica is: (80 mg/m3)/(%SiO2). The NIOSH Sampling Method 7501 for Amorphous Silica calculates the %SiO2 based on the percentage of crystalline silica in the sample. Because the percentage of crystalline silica in aerogel is 0%, OSHA’s particulate limits of 15 mg/m3 (total dust) and 5 mg/m3 (respirable dust) apply to Aerogel exposure. The US National Institute for Occupational Safety & Health (NIOSH) standard for amorphous silica is 6 mg/m3. The German MAK for amorphous silica is 4 mg/m3 (inhalable fraction).
The American Conference of Governmental Industrial Hygienists (ACGIH) withdrew their threshold limit values (TLV) for amorphous silica in 2005 due to insufficient data on single substance exposure. The withdrawn ACGIH TLVs which included co-exposure with crystalline silica were: 10 mg/m3 (total dust) and 3 mg/m3 (respirable dust). The ACGIH recommendations for Particles (insoluble or poorly soluble) Not Otherwise Specified [PNOS] are maintaining airborne concentrations below 3 mg/m3, respirable particles, and 10 mg/m3, inhalable particles.
During industrial hygiene studies conducted during Aerogel fabrication operations, total dust concentrations ranged from 0.44 to 4.6 mg/m3 and respirable dust concentrations ranged from <0.15 to 1.2 mg/m3.
Yes. Aspen Aerogel products comply with the EC Directive 2002/95/EC on the Restriction of Certain Hazardous Substances in Electrical and Electronic Equipment (RoHS Directive). Based on XRay Fluorescence (XRF), Aspen Aerogel products do not contain more than the indicated maximum concentration values by weight in homogeneous materials of the following substances:
Restricted Chemical Substances
Maximum Concentration Value
Hexavalent Chromium (Cr+6)
Polybrominated Biphenyls (PBBs)
Polybrominated Diphenyl Ethers (PBDEs)
Aspen Aerogels insulation blanket is composed primarily of synthetic amorphous silica impregnated onto a fabric material. The final product does not contain any liquid material. Scrap aerogel blanket can be disposed in landfills that are approved to accept industrial waste. Scrap aerogel blankets will generate dust during landfill operations. Industrial waste landfills should be informed of the potential for dust generation during the waste approval process. Scrap materials from Aspen’s Manufacturing operations are disposed in a licensed, industrial landfill in Massachusetts.
To meet customer demands, Aspen Aerogels may use a variety of aerogel additives and fabric substrate materials. These additives may include materials such as carbon black, titanium dioxide and aluminum oxide. Aerogel blankets do not meet any of the characteristics of a US EPA hazardous waste [40 CFR Part 40, Subpart C].
An independent laboratory measured the Minimum Exposable Concentration (MEC) for Aerogel dust to be 575 g/m3 per ASTM E1515-03, "Standard Test Method for Minimum Exposable Concentration of Combustible Dusts”. The laboratory also performed a Minimum Ignition Energy (MIE) test on the dust per ASTM E2019-03, “Standard Test Method for Minimum Ignition Energy of a Dust Cloud in Air”. No ignition was observed at 28.8 Joules Capacitor Stored Energy, the maximum capacitor stored energy delivered by Electrostatic Discharge Tester used for the test.