The Division of Criteria Documentation and Standards Development, National Institute for Occupational Safety and Health, had primary responsibility for development of the criteria and the recommended standard for fibrous glass. The division review staff for this document consisted of Douglas L.#
In developing these recommendations, the Institute proposes that two categories of fibrous glass be identified for control purposes. The delineation between categories is by fiber diameter, with 3.5 micrometers (Aim) being the dividing line. The primary health effects associated with the larger diameter fibers involve skin, eye, and upper respiratory tract irritation, a relatively low incidence of fibrotic (lung) changes, and preliminary indications of a slight excess mortality risk due to nonmalignant respiratory diseases. In this regard, NIOSH considers the hazard potential of fibrous glass to be greater than that of nuisance dust, but less than that of coal dust or quartz.
With small-diameter fibers, much less information on health effects is available. Experimental studies in animals have demonstrated .carcinogenicity; however, with the test methods employed (implantation), it is not considered that these results, can be extrapolated directly to conditions of human exposure. On the basis of currently available information, NIOSH does not consider fibrous glass to be a substance that produces cancers as a result of occupational exposure. However, these smaller fibers can penetrate more deeply into the lungs than larger fibers and until more definitive information is available, the possibility of potentially hazardous effects warrant special consideration.
The recommended environmental levels are based on evidence in those instances where exposure to asbestos and fibrous glass can be compared and, considering the limitations and deficiencies of such data, fibrous glass seems to be considerably less hazardous than asbestos. In addition, although this criteria document addresses occupational exposure to fibrous glass, NIOSH considers that until more information is available, the recommended standard can also be applied to other man-made mineral fibers.
Fibrous glass is the name for a manufactured fiber in which the fiber-forming substance is glass. Glasses are a class of materials made from mixtures of silicon dioxide with oxides of various metals and other elements, that solidify from the molten state without crystallization, A fiber is considered to be a particle with a length-to-diameter ratio of 3 to 1 or greater. An "action level" is defined as half the recommended timeweighted average (TWA) environmental limit. "Occupational exposure" is defined as exposure to airborne fibrous glass above the action level. In addition, because workers may be exposed to fibrous glass by dermal or eye contact occupational exposure includes contact with the skin and eyes to fibrous glass where it is manufactured, used, handled or stored. When environmental concentrations are at or below the action level, adherence to sections 1, 2(b), 4(c), and 8(b) is not required.

# Section 1 -Environmental (Workplace Air) (a) Concentration
Occupational exposure to fibrous glass shall be controlled so that no worker is exposed at an airborne concentration greater than 3,000,000
fibers

# RESPIRATOR SELECTION GUIDE FOR FIBROUS GLASS

# Fibrous Glass Concentration
Less than or equal to 15,000,000 fibers/cu m Less than or equal to 30,000,000 fibers/cu m Less than or equal to 150,000,000 fibers/cu m Less than or equal to 3,000,000,000 fibers/cu m Greater than 3,000,000,000 fibers/ cu m.
Respirator Type Approved Under Provisions of 30 CFR 11
(1) A dust and mist respirator.
(1) A dust and mist respirator except single-use or quarter-mask respirator; or (2) A high efficiency particulate filter respirator; or (3) A supplied-air respirator; or (4) A self-contained breathing apparatus.
(1) A high-efficiency particulate filter respirator with full faceplece; or (2) A supplied-air respirator with a full facepiece, helmet, or hood; or (3) A self-contained breathing apparatus with a full facepiece.
(1) A powered air-purifying respirator with a high efficiency particulate filter and full facepiece; or (2) A type C supplied-air respirator operated in pressure-demand or other positive pressure or continuous flow mode.
(1) A combination respirator which Includes a type C supplied-air respirator operated in pressure-demand'or continuous flow mode; or

# RESPIRATOR SELECTION GUIDE FOR FIBROUS GLASS TABLE 1-1 (CONTINUED)
Fibrous Glass Concentration Respirator Type Approved Under Provisions of 30 CFR 11 Greater than 3,000,000,000 fibers/cu m.
(2) Self-contained breathing apparatus with full facepiece, pressure-demand or other positive pressure mode.

# Section 5 -Informing Employees of Hazards from Fibrous Glass (a)
Workers initially assigned or reassigned to jobs involving occupational exposure to fibrous glass shall be informed of the hazards, symptoms of overexposure (including information on the characteristics of onset and stages of illness), appropriate procedures to be taken in the event of an emergency, precautions to ensure safe use, and to minimize exposure. Workers shall be advised of the availability of relevant information, including that prescribed in (c) below. This information shall be accessible to each worker occupationally exposed to fibrous glass. Where a local exhaust ventilation and collection system is used, it shall be designed and maintained to prevent the accumulation of fibrous glass.
(1) Where materials containing fibrous glass are mechanically worked by power equipment, exhaust ventilation shall be used to limit airborne fibrous glass.
(2) Air from exhaust ventilation systems shall not be recirculated into the workroom.

# (b) General Work Practices and Environmental Controls
A variety of situations exist that involve potential exposure to fibrous glass. To specifically detail work practices and controls for each situation would be impractical. In operations where there is occupational exposure to fibrous glass, employers shall develop comprehensive work practices relevant to the specific situations encountered. These practices should follow the recommended guidelines identified in this section, in Chapter VI, and in Appendix VI. Generally, occupational exposure to fibrous glass can occur in either stationary operations or in operations that regularly occur at different (nonstationary) locations. The general principles to follow in these operations have been identified and are given below.
(1) Stationary Operations
Operations that involve regular handling of fibrous glass at a fixed location, such as manufacturing, shall be controlled by using appropriate enclosures and well-designed local exhaust systems.
Procedures shall be established that minimize the accumulation of waste dust or scrap materials. Specific procedures for containment of dust and handling of contained materials shall be instituted so that the possibility of secondary air contamination is minimized. Cleanup procedures based on wetting the material and use of vacuum-cleaning for pickup shall be employed.

# (g) General Housekeeping
(1) Fibrous glass waste and scrap shall be collected and disposed of in a manner which will minimize its dispersal into the atmosphere.
(2) Emphasis shall be placed on covering waste containers, proper storage of materials, and collection of fibrous glass dust.
(3) Cleanup of fibrous glass dust shall be performed using vacuum cleaners or wet cleaning methods. Dry sweeping shall not be performed.

# (b) Personal Monitoring
(1) A program of personal monitoring shall be instituted to identify and measure, or permit calculation of, the exposures of all employees occupationally exposed to fibrous glass above the action level.
Point source and area monitoring may be used to supplement personal monitoring.
In all personal monitoring, samples representative of exposure in the breathing zone of the employee shall be collected.
Procedures for sampling, calibration of equipment, and analysis of fibrous glass in samples shall be as provided in Section 1(b). This sampling and analysis shall be conducted every 3 months on at least 25% of the workers so that each worker's exposure is measured at least every year; the frequency of sampling and the fraction of employees sampled may be different if so directed by a professional industrial hygienist.
(   1945 to 1952, 1953 to 1957, 1958 to 1962, 1963 to 1967, and 1968  No differences in tissue reactions between the three groups were detected; however, there were differences between the exposed anz the control animals.
In the exposed rats, pneumonia and endemic chronic bronchitis and its sequelae were found at a higher, but unspecified, rate than in unexposed rats. Pneumonia, however, is a normal finding in aged laboratory rats. Exposed rats showed an accumulation of dust-filled macrophages within alveoli. A few foci of septal collagenous fibrosis were seen in some rats, but there was no other evidence of fibrosis. A large amount of dust in some of the satellite lymph nodes was found in rats after 2 years of exposure.
In the hamsters, macrophage-containing alveoli clustered around respiratory bronchioles. Alveolar ducts contained dustfilled macrophages. Ferruginous bodies were observed.
In contrast to the satellite lymph nodes of rats, those of hamsters were not enlarged even at 24 months .

# Botham and Holt
, in 1971, investigated the production of ferruginous bodies after inhalation of glass fibers and described their evolution in some detail. Eighteen male guinea pigs were exposed once for 24 hours to glass fibers that were mostly 20 pm in length or shorter and less than 3 pm diameter, mostly less than 1 pm. Fibers measuring 40 pm in length were noted rarely. The exposure concentration was described only as "high."
The animals were killed and examined at various intervals after exposure. In the lungs most of the fibers that were visible with the light microscope were less than 20 pm in length; fibers longer than 40 pm were rarely observed. Fibers retained in the lungs deposited initially in the bronchioles. Some fibers moved inward to the alveoli, where they were taken up by macrophages, some of which then combined to form giant cells.     These observations indicate that concern must be given to all sizes of glass fibers and not to a specific size alone if the total occupational health problem associated with fibrous glass exposure is to be adequately controlled.    for small-diameter fibers and a gravimetric method has been recommended for all glass fibers but which will essentially estimate large fiber exposure.

# The presence of fibers was

# A summary of the effects from various exposures to fibrous glass is presented in
When both analytical methods are used, estimates of exposure should be accurate to within known limitations regardless of fiber size present in workplace air.

# Environmental Concentrations
It is important to recognize that in virtually all occupational situations where fibrous glass is present, the exposure is not to fibers of uniform diameter, but to a range which usually includes a substantial percentage of fibers having diameters considered to be of respirable size. The median length ranged from 19 to 70 pm.

# Balzer
In facilities where small-diameter fibers were present, fibers ranged from less than 0.1 to 2.0 pm with the majority being less than 1.0 pm and 40 to 85% less than 0.5 pm.
Mean airborne fiber counts for these facilities ranged from 1,000,000 to 21,900,000 fibers/cu m (1.0 to 21.9 fibers/cc); the single highest concentration was 44,100,000 fibers/cu m (44.1 fibers/cc). In bulk handling operations, four of six facilities had a mean concentration in excess of 5,000,000 fibers/cu m (5.0 fibers/cc).   can similarly be recalculated to show that airborne concentration of fibers under 3.5 pm in diameter and longer than 5 pm in length were well below (100,000 fibers/cu m) 0.1 fiber/cc.

# All operations studied had mean gravimetric concentrations

# Environmental levels for various operations involving fibrous glass
are summarized in Tables XV-12 to XV-14.

# Engineering Controls
Studies of various facilities using or producing fibrous glass with diameters greater than 3.5 pm have indicated that airborne fiber concentrations generally are less than (1,000,000 fibers/cu m) 1.0 fiber/cc in fiber-counts and less than 2 mg/cu m by gravimetric measurement , At times, in operations involving fibrous glass with diameters less than 3.5 pm airborne fiber concentrations have been found to be much higher, with mean counts ranging from 1,000,000 to 21,900,000 fibers/cu m.
The smaller diameter fibers are the ones that are usually found in the greatest concentrations. These are the fibers that should be most strictly controlled. an "inert" or nuisance particulate for which a TLV of 50 mppcf or 15 mg/cu m, whichever is less, of total dust less than 1% Si02 was suggested, with the provision that this applied to fibrous glass of less than 5-7 pm in diameter. No TLV for coarse fibrous glass had been set at that time.
In 1970, fibrous glass was listed as a nuisance dust in both the adopted and the proposed lists of the ACGIH, the TLV for such dusts being lowered to 30 mppcf or 10 mg/cu m, whichever was less, of total dust less than 1% Si02 Respirators are recommended where engineering controls cannot be applied in operations involving fibrous glass 1 pm or less in diameter, because of the extreme respirability of such fibers. These fibers have not been shown to regularly produce pathologic effects in the respiratory system after occupational exposure. However, these kinds of exposures have been few in number and only of recent occurrence, so that all consequences of exposures may not be manifested yet. To insure that very small fibers (those less than 1 pm in diameter) will not penetrate the lungs it is suggested that in situations where there is exposure to these fibers that respirators be used even if engineering controls are present.

# I I (e) Informing Employees of Hazards
Employees shall be informed of hazards associated with exposure to fibrous glass so that they may know the reasons for recommended practices, limits, and controls. The basis for work practices to be applied with fibrous glass is that exposure may be minimized by reducing the likelihood that fibrous glass will be made airborne or allowed to contact skin or eyes.

# (c) Equipment
The sampling train consists of a membrane filter and a vacuum pump.
( A collection efficiency of greater than 98.7% was determined for the collection medium at the 2X level; thus, no bias was introduced in the sample collection step. Likewise, no significant bias in the analytical method is expected other than normal gravimetric errors.
The coefficient of variation is a satisfactory measure of both accuracy and precision of the sampling and analytical method.

# Advantages and Disadvantages of the Method
The analysis is simple but the method is nonspecific and subject to interference due to presence of other nonvolatile or combustible particulates in the air being sampled.

# Apparatus (a) Sampling Equipment
The sampling unit for the collection of personal air samples for the determination of fibrous glass has the following components:
(1) The filter unit, consisting of the filter media, cellulose supported pad and 37-mm three-piece cassette filter holder.
(2) Personal sampling pump: A calibrated personal sampling pump whose flow can be determined to an accuracy of +5% at the recommended flowrate.
The pump must be calibrated with a filter holder and filter in the line.
(3) Thermometer.
(4) Manometer.

# The authors
 recognized the possibility of worker exposure from sources
The prevalence of radiographic abnormalities in the chests of fiber glass workers.    The method may be extended to higher sample concentrations by collecting a smaller sample volume; however, no more than 1.5 to 2 mg of material should be collected on any filter because greater amounts will be lost due to flaking.

# Interferences
The presence of any other particulate material in the air being sampled will be a positive interference since this is a gravimetric method.
Those materials that volatilize or combust at 600 C or less will not be interferences.
Information on any other particulate materials present should be solicited. If the concentration of other particles is known, then the fibrous glass concentration can be determined by the difference. If other particulate matter is known to be present and its concentration cannot be determined, then this method will not provide a limited measure of the fibrous glass concentration.

# Precision and Accuracy
The precision and accuracy of the total sampling and analytical method has not been determined specifically for fibrous glass; however, it has been determined for other substances, such as carbon black, with a similar recommended limit. For carbon black, the coefficient of variation for the total analytical and sampling method in the range of 1.86-7  MATERIAL SAFETY DATA SHEET  (2) Prewetting of materials to be torn out.

# S P E C IF IC G R A V IT Y { H jO M ) V A P O R P R E S S U R E V A P O R D E N S IT Y ( A IR M ) S O L U B IL IT Y IN H 20 . % B Y WT % V O L A T lL E S B Y V O L E V A P O R A T IO N R A T E (B U T Y L A C E T A T E ; 1) A P P E A R A N C E
(3) Isolation of areas where "tear-out" is taking place with curtains and portable partitions.

# XV. TABLES AND FIGURE