Definitions and Notations

Definitions

Documentation

This is the source publication that provides the critical evaluation of the pertinent scientific information and data with reference to literature sources upon which each TLV or BEI is based. See the discussion under “TLV/BEI Development Process: An Overview” found at the beginning of this book. The general outline used when preparing the Documentation may be found in the Operations Manual of the Threshold Limit Values for Chemical Substances (TLV-CS) Committee, accessible online at: acgih.org/about/volunteer-leadership/committees/committee-operations-manuals.

Minimal Oxygen Content

An oxygen (O₂)-deficient atmosphere is defined as one with an ambient pO₂ less than 132 torr.¹ The minimum requirement of 19.5% oxygen at sea level (148 torr O₂, dry air) provides an adequate amount of oxygen for most work assignments and includes a margin of safety.^2,3 Studies of pulmonary physiology suggest that the above requirements provide an adequate level of oxygen pressure in the lungs (alveolar pO₂ of 60 torr).^4-6

Some gases and vapors, when present in high concentrations in air, act primarily as simple asphyxiants, without other significant physiologic effects. A simple asphyxiant may not be assigned a TLV because the limiting factor is the available oxygen. Atmospheres deficient in O₂ do not provide adequate warning and most simple asphyxiants are odorless. Account should be taken of this factor in limiting the concentration of the asphyxiant particularly at elevations greater than 5,000 feet where the pO₂ of the atmosphere is less than 120 torr. Several simple asphyxiants present an explosion hazard. (See adopted Appendix F: Minimal Oxygen Content.)

Nanomaterials

Nanomaterials are objects that are 100 nm or smaller in 1 or more dimension. Substances composed of nanomaterials, even when agglomerated, may have greater or different toxicity than the same substance in fine or sometimes called “bulk” form. When supported by the literature, ACGIH may differentiate TLVs for nanomaterials.

Notation

A notation is a designation that appears as a component of the TLV in which specific information is listed in the column devoted to Notations.

Notice of Intended Change (NIC)

The NIC is a list of actions proposed by the TLV-CS Committee for the coming year. This Notice provides an opportunity for public comment. Values remain on the NIC for a minimum of 1 comment period after they have been ratified by the ACGIH Board of Directors. The proposals should be considered trial values during the period they are on the NIC. If the Committee neither finds nor receives any substantive data that change its scientific opinion regarding an NIC TLV, the Committee may then approve its recommendation to the ACGIH Board of Directors for adoption. If the Committee finds or receives substantive data that change its scientific opinion regarding an NIC TLV, the Committee may change its recommendation to the ACGIH Board of Directors for the matter to be either retained on or withdrawn from the NIC. Values appearing in parentheses in the Adopted TLV section are to be used during the period in which a proposed change for that value or notation appears on the NIC.

Particulate Matter/Particle Size

For solid and liquid particulate matter, TLVs are expressed in terms of total particulate matter, except where the terms inhalable, thoracic, or respirable particulate matter are used. The intent of ACGIH is to replace all total particulate TLVs with inhalable, thoracic, or respirable particulate mass TLVs. Side-by-side sampling using “total” and inhalable, thoracic, or respirable sampling techniques is encouraged to aid in the replacement of current total particulate TLVs. See Appendix C: Particle Size-Selective Sampling Criteria for Airborne Particulate Matter, for the definitions of inhalable, thoracic, and respirable particulate matter.

Particles (insoluble or poorly soluble) Not Otherwise Specified (PNOS)

There are many insoluble particles of low toxicity for which no TLV has been established. ACGIH believes that even biologically inert, insoluble, or poorly soluble particles may have adverse effects and suggests that airborne concentrations should be kept below 3 mg/m³, respirable particles, and 10 mg/m³, inhalable particles, until such time as a TLV is set for a particular substance. A description of the rationale for this recommendation and the criteria for substances to which it pertains are provided in Appendix B.

TLV Basis

TLVs are derived from publicly available information summarized in their respective Documentation. Although adherence to the TLV may prevent several adverse health effects, it is not possible to list all of them in this book. The basis on which the values are established will differ from agent to agent (e.g., protection against impairment of health may be a guiding factor for some, whereas reasonable freedom from irritation, narcosis, nuisance, or other forms of stress may form the basis for others). Health impairments considered include those that shorten life expectancy, adversely affect reproductive function or developmental processes, compromise organ or tissue function, or impair the capability for resisting other toxic substances or disease processes.

The TLV Basis represents the adverse effect(s) upon which the TLV is based. The TLV Basis column in this book is intended to provide a field reference for symptoms of overexposure and as a guide for determining whether components of a mixed exposure should be considered as acting independently or additively. Use of the TLV Basis column is not a substitute for reading the Documentation. Each Documentation is a critical component for proper use of the TLV(s) and to understand the TLV basis. A complete list of the TLV bases used by the Threshold Limit Values for Chemical Substances Committee may be found in their Operations Manual online at: acgih.org/about/volunteer-leadership/committees/committee-operations-manuals/.

Abbreviations used

card = cardiac
CNS = central nervous system
COHb-emia = carboxyhemoglobiemia
convul = convulsion
dam = damage
eff = effects
form = formation
func = function
GI = gastrointestinal
Hb = hemoglobin
impair = impairment
inhib = inhibition
irr = irritation
LRT = lower respiratory tract
MeHb-emia = methemoglobinemia
PNS = peripheral nervous system
pulm = pulmonary
repro = reproductive
resp = respiratory
sens = sensitization
URT = upper respiratory tract

Notations/Endnotes

Biological Exposure Indices (BEIs)

The notation BEI is listed in the Notations column when a BEI (or BEIs) is (are) also recommended for the substance. Three subcategories of the BEI notation have been added to help the user identify those substances that would use only the BEI for cholinesterase-inhibiting pesticides or methemoglobin inducers. They are as follows:

BEI_C = See the BEI for cholinesterase-inhibiting pesticide

BEI_M = See the BEI for methemoglobin inducers

BEI_P = See the BEI for polycyclic aromatic hydrocarbons (PAHs)

Biological monitoring should be instituted for such substances to evaluate the total exposure from all sources, including dermal, ingestion, or nonoccupational. See the BEI section in this book and the Documentation of the TLVs and BEIs for these substances.

Carcinogenicity

A carcinogen is an agent capable of inducing benign or malignant neoplasms. Evidence of carcinogenicity comes from epidemiology, toxicology, and mechanistic studies. Specific notations (i.e., A1, A2, A3, A4, and A5) are used by ACGIH to define the categories for carcinogenicity, and are listed in the Notations column. See Appendix A for these categories and definitions and their relevance to humans in occupational settings.

Inhalable Fraction and Vapor (IFV)

The Inhalable Fraction and Vapor (IFV) endnote is used when a material exerts sufficient vapor pressure such that it may be present in both particle and vapor phases, with each contributing a significant portion of the dose at the TLV-TWA concentration. The ratio of the Saturated Vapor Concentration (SVC) to the TLV-TWA is considered when assigning the IFV endnote. The IFV endnote is typically used for substances with an SVC/TLV ratio between 0.1 and 10.

The industrial hygienist should also consider both particle and vapor phases to assess exposures from spraying operations, from processes involving temperature changes that may affect the physical state of matter, when a significant fraction of the vapor is dissolved into or adsorbed onto particles of another substance, such as water-soluble compounds in high humidity environments.⁷

Ototoxicant

The designation OTO for hearing disorders in the Notations column highlights the potential for a chemical to cause hearing impairment alone or in combination with noise, even below 85 dBA. The OTO notation is reserved for chemicals that have been shown, through evidence from animals or humans, to adversely affect anatomical structure or auditory function, manifested as a permanent audiometric threshold shift and/or difficulties in processing sounds. Some substances appear to act synergistically with noise, whereas others may potentiate noise effects. The OTO notation is intended to focus attention, not only on engineering controls, administrative controls, and PPE needed to reduce airborne concentrations, but also on other means of preventing excessive combined exposures with noise to prevent hearing disorders. Specifically, affected employees may need to be enrolled in hearing conservation and medical surveillance programs to more closely monitor auditory capacity, even when noise exposures do not exceed the TLV for Audible Sound. Please refer to the section on Ototoxicity in the TLV Documentation for Audible Sound. Also see references listed at the end of the Definitions/Notations section.^8-10

Sensitization

The designations DSEN and/or RSEN in the Notations column in the TLVs and BEIs book refer to the potential for an agent to produce dermal and/or respiratory sensitization. RSEN and DSEN are used in place of the SEN notation when specific evidence of sensitization by that route is confirmed with human or animal data. The DSEN and RSEN notations do not imply that sensitization is the critical effect on which the TLV is based, nor do they imply that this effect is the sole basis for that agent’s TLV. If sensitization data exist, they are carefully considered when recommending the TLV for the agent. TLVs that are based upon sensitization are meant to protect workers from induction of this effect. These TLVs are not intended to protect those workers who have already become sensitized.

In the workplace, respiratory or dermal exposures to sensitizing agents may occur. Similarly, sensitizers may evoke respiratory or dermal reactions. The notation does not distinguish between sensitization involving any of these tissues. The absence of a DSEN or RSEN notation does not signify that the agent lacks the ability to produce sensitization but may reflect the paucity or inconclusiveness of scientific evidence.

Sensitization often occurs via an immunologic mechanism and should not be confused with hyperreactivity, susceptibility, or sensitivity. Initially, there may be little or no response to a sensitizing agent. However, after a person is sensitized, subsequent exposure may cause intense responses, even at low exposure concentrations (well below the TLV). These reactions may be life-threatening and may have an immediate or delayed onset. Workers who have become sensitized to a particular agent may also exhibit cross-reactivity to other agents that have similar chemical structures. A reduction in exposure to the sensitizer and its structural analogs generally reduces the frequency or severity of reactions among sensitized individuals. For some sensitized individuals, complete avoidance of exposure to the sensitizer and structural analogs provides the only means to prevent the specific immune response.

Agents that are potent sensitizers present special problems in the workplace. Respiratory and dermal exposures should be significantly reduced or eliminated through process control measures and personal protective equipment. Education and training (e.g., review of potential health effects, safe handling procedures, emergency information) are also necessary for those who work with known sensitizing agents.

For additional information regarding the sensitization potential of a particular agent, refer to the TLV Documentation for the specific agent.

Skin

The designation Skin in the Notations column refers to the potential significant contribution to the overall exposure by the cutaneous route, including mucous membranes and the eyes, by contact with vapors, liquids, and solids. Where dermal application studies have shown absorption that could cause systemic effects following exposure, a Skin notation would be considered. The Skin notation also alerts the industrial hygienist that overexposure may occur following dermal contact with liquid and aerosols, even when airborne exposures are at or below the TLV.

A Skin notation is not applied to chemicals that may cause dermal irritation. However, it may accompany a sensitizer notation for substances that cause respiratory sensitization following dermal exposure. Although not considered when assigning a Skin notation, the industrial hygienist should be aware that there are several factors that may significantly enhance potential skin absorption of a substance that otherwise has low potential for the cutaneous route of entry. Certain vehicles can act as carriers, and when pretreated on the skin or mixed with a substance, can promote the transfer of the substance into the skin. In addition, the existence of some dermatologic conditions can also significantly affect the entry of substances through the skin or wound.

While relatively limited quantitative data currently exist with regard to skin absorption of gases, vapors, and liquids by workers, ACGIH recommends that the integration of data from acute dermal studies and repeated-dose dermal studies in animals and humans, along with the ability of the chemical to be absorbed, be used in deciding on the appropriateness of the Skin notation. In general, available data which suggest that the potential for absorption via the hands and forearms during the workday could be significant, especially for chemicals with lower TLVs, could justify a Skin notation. From acute animal toxicity data, materials having a relatively low dermal LD₅₀ (i.e., 1,000 mg/kg of body weight or less) would be given a Skin notation. When chemicals penetrate the skin easily (i.e., higher octanol–water partition coefficients) and where extrapolations of systemic effects from other routes of exposure suggest dermal absorption may be important in the expressed toxicity, a Skin notation would be considered. A Skin notation is not applied to chemicals that cause irritation or corrosive effects in the absence of systemic toxicity.

Substances having a Skin notation and a low TLV may present special problems for operations involving high airborne concentrations of the material, particularly under conditions where significant areas of the skin are exposed for a long period. Under these conditions, special precautions to significantly reduce or preclude skin contact may be required.

Biological monitoring should be considered to determine the relative contribution to the total dose from exposure via the dermal route. ACGIH recommends a number of adopted BEIs that provide an additional tool when assessing the total worker exposure to selected materials. For additional information, refer to ‘Dermal Absorption’ in the “Introduction to the Biological Exposure Indices,” Documentation of the BEIs,¹¹ and to Leung and Paustenbach.¹² Other selected readings on skin absorption and the skin notation include Sartorelli,¹³ Schneider et al.,¹⁴ Wester and Maibach,¹⁵ Kennedy et al.,¹⁶ Fiserova-Bergerova et al.,¹⁷ and Scansetti et al.¹⁸

The use of a Skin notation is intended to alert the reader that air sampling alone is insufficient to quantify exposure accurately and that measures to prevent significant cutaneous absorption may be required.

References

1. National Institute for Occupational Safety and Health: Working in confined spaces. DHHS (NIOSH) Pub. No. 80-106. 1980. Cincinnati (OH): NIOSH.
2. National Institute for Occupational Safety and Health. NIOSH respirator decision logic. DHHS (NIOSH) Pub. No. 87-108. 1987. Cincinnati (OH): NIOSH.
3. McManus N. Safety and health in confined spaces. 1999. Boca Raton (FL): Lewis Publishers.
4. Silverthorn DE: Human physiology: an integrated approach. 2nd ed. 2001. New Jersey (NJ): Prentice-Hall.
5. Guyton AC. Textbook of medical physiology. 8th ed. 1991. Philadelphia (PA): WB Sanders Co.
6. National Institute for Occupational Safety and Health. A guide to industrial respiratory protection, DHEW (NIOSH) Pub. No. 76-198. 1976. Cincinnati (OH): NIOSH.
7. Perez C, Soderholm SC, Some chemicals requiring special consideration when deciding whether to sample the particle, vapor, or both phases of an atmosphere. Appl Occup Environ Hyg. 1991; 6:859-864.
8. Campo P, Morata TC, Hong O. Chemical exposure and hearing loss. Disease-a-Month. 2013; 59:119-138. doi: 10.1016/j.disamonth.2013.01.003.
9. Hoet P, Lison D, Ototoxicity of toluene and styrene: state of current knowledge. Crit Rev Toxicol. 2008; 38:127-170.
10. Morata TC, Campo O. Ototoxic effects of styrene alone or in concert with other agents: A review. Noise & Health. 2002; 4(14):15-24.
11. American Conference of Governmental Industrial Hygienists. Dermal absorption. In: Documentation of the Biological Exposure Indices. 7th ed. 2001. Cincinnati (OH): ACGIH. pp. 21-26.
12. Leung H, Paustenbach DJ. Techniques for estimating the percutaneous absorption of chemicals due to occupational and environmental exposure. Appl Occup Environ Hyg. 1994; 9(3):187-197.
13. Sartorelli P. Dermal risk assessment in occupational medicine. Med Lav. 2000; 91(3):183-191.
14. Schneider T, Cherrie JW, Vermeulen R, Kromhout H. Dermal exposure assessment. Ann Occup Hyg. 2000; 44(7):493-499.
15. Wester RC, Maibach HI. Understanding percutaneous absorption for occupational health and safety. Int J Occup Environ Health. 2000; 6(2):86-92.
16. Kennedy Jr GL; Brock WJ; Banerjee AK. Assignment of skin notation for threshold limit values chemicals based on acute dermal toxicity. Appl Occup Environ Hyg. 1993; 8(1):26-30.
17. Fiserova-Bergerova V, Pierce JT, Droz PO. Dermal absorption potential of industrial chemicals: Criteria for skin notation. Am J Ind Med. 1990; 17(5):617-635.
18. Scansetti G, Piolatto G, Rubino GF. Skin notation in the context of workplace exposure standards. Am J Ind Med 1988; 14(6):725-732.