Airborne concentrations of asbestos in 71 school buildings

Our plain-English summary of Airborne concentrations of asbestos in 71 school buildings, by M. Corn, K. Crump, D.B. Farrar, et al (Regulatory Toxicology and Pharmacology, 1991).

The study

• Authors: M. Corn, K. Crump, D.B. Farrar, R.J. Lee, D.R. McFee
• Journal: Regulatory Toxicology and Pharmacology
• Published: 1991;13(1):99-114
• Cited by: 22 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 004464).

Abstract

A total of 473 air samples from 71 schools scheduled for abatement (328 indoor static samples, 51 personal samples, and 94 outdoor samples) were analyzed by transmission electron microscopy techniques. Six measures of asbestos-in-air concentration were considered: (1) total asbestos structures per cubic centimeter: (2) chrysotile structures per cubic centimeter; (3) amphibole structures per cubic centimeter; (4) structures per cubic centimeter at least 0.5 micron long and at least five times wide; (5) structures per cubic centimeter at least 5 microns long; and (6) structures per cubic centimeter at least 5 microns long and at least 0.2 micron wide. The average concentration of chrysotile structures in indoor air samples was 0.017 structures/cm3; the average concentration of amphibole structures was 0.0015 structure/cm3. Ninety-five percent of structures found were chrysotile. The average concentrations of all structures were significantly higher indoors than outdoors (P less than 0.001). The average concentration of structures more than 5 microns long indoors was 0.00023 structure/cm3. None of the following factors were significantly correlated with asbestos concentrations in air: type of asbestos-containing materials (ACM) present, condition of ACM, accessibility of ACM to students, whether ACM were covered, air flow, or whether sweeping was noted during sample collection. In addition, asbestos-in-air concentrations were not significantly different in different types of schools (high, intermediate or elementary) or in schools constructed in different time periods. Lastly, there was no correlation between the mineral type of asbestos found in the air and the type found in samples of bulk material.

In plain English

The authors measured airborne asbestos in 71 U.S. schools scheduled for asbestos abatement. The air samples came from a pool collected by defendants preparing for litigation. Using transmission electron microscopy, they analyzed 473 samples: 328 indoor static, 51 personal and 94 outdoor. Indoors, the average was 0.020 asbestos structures per cubic centimetre in total and 0.00023 for structures longer than 5 micrometres. The outdoor averages were 0.002 and 0.0. Indoor levels were significantly higher than outdoor levels. About 95% of structures were chrysotile, and most were very thin and short. Airborne levels were not significantly correlated with the type, condition, accessibility or covering of asbestos-containing materials, with air flow, or with sweeping. School type and construction period also showed no significant difference, but levels differed significantly by state. Amosite in building materials was not linked to more amphibole in the air. The authors concluded that the presence and condition of asbestos-containing materials were not conclusively correlated with airborne levels. They noted that these schools, all involved in litigation, do not represent all U.S. schools.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Air sampling survey (measurement study) of schools, using samples selected from a pool collected by defendants in litigation and analyzed by transmission electron microscopy
• Who was studied: 71 schools scheduled for abatement and involved in litigation: 44 in Texas, 15 in Colorado, 4 in Michigan, 3 in Ohio, 2 in Pennsylvania, and 1 each in Florida, Tennessee and Massachusetts. 473 air samples in total: 328 indoor static, 51 personal (worn by a survey team member, not by building occupants) and 94 outdoor. Sampling dates are not given.
• Exposure: Airborne asbestos structures in school air, counted as total, chrysotile and amphibole structures, and by size. Asbestos-containing materials present included plaster ceilings, fireproofing and brake linings. Bulk samples from 70 schools showed chrysotile in all 69 schools where asbestos was found, amosite in 7 schools, and trace amounts of tremolite or other amphibole in 5 additional schools. All amphiboles were reported as asbestos even though most observed were not asbestiform.
• Main results:
  • Indoor samples averaged 0.020 structure/cm3 for total structures and 0.00023 structure/cm3 for structures longer than 5 micrometres. Outdoor samples averaged 0.002 and 0.0; no structures longer than 5 micrometres were found outdoors.
  • Total asbestos structures averaged significantly higher indoors than outdoors (P less than 0.001), and the difference was significant for the other five concentration measures as well.
  • In indoor air samples, chrysotile structures averaged 0.017 structures/cm3 and amphibole structures averaged 0.0015 structure/cm3.
  • Personal samples were significantly higher than outdoor air and not different from indoor air. Airborne levels did not differ significantly by how an area was used.
  • Type, condition, accessibility and covering of asbestos-containing materials, air flow, and sweeping were not significantly correlated with airborne levels. Areas with asbestos-containing materials were almost significantly higher (P = 0.082) than areas in the same building without them.
  • Levels did not differ significantly by school type (P = 0.18) or construction period (P = 0.063). They did differ significantly by state, and the authors could not determine why.
  • Outdoor concentrations were significantly lower on days with some precipitation (P = 0.005, 84 samples). Lower temperatures were associated with higher outdoor levels (P = 0.016, 84 samples). Wind direction (P = 0.6) and motor traffic (P = 0.29, 47 samples) were not significant.
  • Most fibers were very thin (94% less than 0.2 micrometre in diameter) and short (76% less than 1.0 micrometre long), and 95% were chrysotile. Amphibole fibers tended to be somewhat longer and thicker.
  • In the 7 schools with significant amosite in bulk samples, neither the amount nor the percentage of airborne amphibole was significantly higher. Airborne amphibole percentages were generally lower in those 7 schools than in the remaining 62.
  • The highest single indoor or personal reading for structures longer than 5 micrometres was 0.012, which the authors described as 6% of the OSHA standard of 0.2. They suggested that high peak exposures rarely occur in schools.
• The authors' conclusion: The authors concluded that neither the presence nor the condition of asbestos-containing materials in sampled areas was conclusively correlated with airborne asbestos concentrations, and that the study gave no conclusive evidence that these materials make a significant contribution to airborne asbestos levels in schools.
• Limitations the authors state:
  • All the schools were involved in asbestos removal litigation, so they do not represent all U.S. schools.
  • Because all but at most two schools contained asbestos-containing materials, the authors could not directly test whether levels are higher in schools with these materials than in schools without them.
  • The aggressive sampling procedures of the EPA protocol were not followed.
  • Data on the possible explanatory factors were not collected for all samples.
  • Because precipitation lowered outdoor levels, the authors cautioned against attributing the indoor-outdoor difference to in-place asbestos-containing materials.

Topics

Medical terms in this study, explained in our Lexicon: Abatement, Personal Breathing Zone Sample, Transmission Electron Microscopy (TEM), Chrysotile, Amphibole Group, Asbestos-Containing Material (ACM).

Related studies

• Airborne asbestos levels in school buildings in Italy — A. Campopiano, S. Casciardi, et al. (2004)
• Asbestos in New York City public school buildings--public policy: is there a scientific basis? — R. Wilson, A.M. Langer, et al. (1994)
• Asbestos in school buildings: results of a nation-wide survey — K.Z. Silver (1979)
• Statistical analysis of data on airborne asbestos levels collected in an EPA survey of public buildings — K.S. Crump, D.B. Farrar (1989)
• A radiographic survey of public school building maintenance and custodial employees — H.A. Anderson, L.P. Hanrahan, et al. (1992)
• Asbestos-related disease in custodial and building maintenance workers from a large municipal school district — J.R. Balmes, A. Daponte, et al. (1991)

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