In 2019, 1,762,450 new cancer cases and 606,880 cancer deaths are projected to occur in the United States1. It is statistically improbable for someone in America not to know someone close who had or has cancer.


Knowledge of occupational carcinogens has seen rapid advancement. IARC Monographs, the world’s most comprehensive source of carcinogens, started in 1971 and listed 28 Group 1, “Carcinogenic to humans” agents with occupational exposure in 2004 – that number rose to 47 agents by 20172.

IARC includes about 900 agents with less evidence of human carcinogenicity such as Group 2A “Probably” (82 agents); Group 2B “Possibly” (311 agents); Group 3 “Not classifiable” (499 agents); and Group 4 “Probably not” (1 agent).

 Lead is an IARC Group 2B agent while inorganic lead compounds fall into Group 2A. Welding fumes, both stainless and mild steels, joined IARC’s Group 1 list in 2017.

Be aware that other organizations such as NTP, EPA, OSHA, NIOSH, state OSHA programs, such as Cal-OSHA and chemical manufacturers may classify carcinogens by various means — strength and weight of evidence and with different terminologies. OSHA HazCom/GHS 29 CFR 1910.1200 Appendix A.6 describes carcinogenicity by categories — Category 1A for known human carcinogen, human evidence.


Understanding the basics of chemical dose-response curves helps to appreciate chemical carcinogens. A common usage of the linear dose-response curve for most chemicals is that U.S. OELs (Occupational Exposures Limits), such as the PEL, REL and TLV, and the worker DNEL (Derived No Effect Level) established by chemical manufacturers, are set many times below the LOAEL (Lowest Observed-Adverse Effect Level).

When linear dose-response curves are understood by workers, they may be given assurances that exposures below the OEL/DNEL may be experienced 8-hours/day, 40-hours/week, 50-weeks/year, for a working lifetime (45 years) without any adverse health effect. Workers with this knowledge may appreciate that exposures above an OEL/DNEL for short times are unlikely to cause harm. Knowledge on this logic eases controversy among pros. This logic is also known as health-based limits.

Linear dose-response logic, however, doesn’t hold true for some chemicals, particularly occupational carcinogens. There is some risk of cancer even at the lowest measurable exposure. In 2016, NIOSH announced that RELs would no longer apply for occupational carcinogens3.

Rather, a new OEL “risk management limit for a carcinogen” or RML-CA would be developed. NIOSH defines RML-CA as the “maximum 8-hour time-weighted average concentration of an occupational carcinogen above which a worker should not be exposed.” Chemical manufacturers required to develop the worker DNEL that has a similar definition to NIOSH RML-CA, are also required to develop a DMEL (Derived Minimal Effect Level) for chemicals that demonstrate carcinogenicity. RML-CA and DMEL are examples of risk-based limits.

Risk communication

A major distinction between health-based and risk-based limits centers on risk communication. Health-based limits, for example, offer reasonable assurances of no harm over a working lifetime of exposure. Risk-based limits, however, should be communicated in terms such as:

  • Lifetime excess risk of getting cancer at the RML-CA is about 1 in 10,000.
  • Lifetime excess risk of getting cancer at the DMEL is not clearly defined but is generally 1 in 25,000.
  • Lifetime excess risk of getting cancer at the PEL for an OSHA carcinogen is generally 1 in 1,000.

Managing carcinogens

How do you beat the odds of acquiring cancer from exposure to an occupational carcinogen? How is fear of cancer managed? Here are eight priority actions:

  • Policy and Procedure. Organizations must establish, communicate, and audit site-specific written cancer policy and procedures. Without this mechanism, there is no effective management for occupational carcinogens.
  • Compliance. OSHA regulates about 30 carcinogens. Organizations must comply with these regulations.
  • Conformance. Conformance means voluntarily actions beyond regulations. What are the carcinogens — known, probable, possible, or not classifiable, chemical or not — radiation or biological, that will be voluntarily managed beyond OSHA? OSHA doesn’t regulate welding fumes (whole component) as a carcinogen. Welding fumes (include UV), however, are an IARC Group 1 carcinogen.  Most organizations should manage all known carcinogens. 
  • Inventory. An inventory -- location, number of workers exposed, etc. of managed carcinogens -- must be established, maintained and differentiated from other chemicals.
  • Hierarchy of controls. Exposure to carcinogens are reduced through hierarchy of controls, beginning with elimination and substitution, where practical. Do not discourage voluntary use of respiratory protection.
  • Continual improvement. There is some risk of cancer even at the lowest measurable exposure. Reduce risk by continual reduction of exposure. Set target dates to reduce exposure by 10%, 20%, or whatever, through the hierarchy of controls. Measure reductions no less than annually.
  • Communication. Communication means sending a message and receiving feedback that the message is understood.
  • Continual learning. Cancer surveillance registries remain the only non-communicable disease that must be legally tracked throughout the U.S. The Firefighter Cancer Registry Act of 2018 (follow ripples back to 9/11), for example, brings focus on some occupations. Registry databases are accessible to researchers. Requirements of OSHA 1910.1020 may include a cancer database.


  1. Cancer statistics, 2019: Rebecca L. Siegel MPH, Kimberly D. Miller MPH, Ahmedin Jemal DVM, PhD, First published: 08 January 2019.
  2. Loomis D, Guha N, Hall AL, et al, Identifying occupational carcinogens: an update from the IARC Monographs, Occup Environ Med 2018;75:593-603.
  3. NIOSH [2016]. Current intelligence bulletin 68: NIOSH chemical carcinogen policy. By Whittaker C, Rice F, McKernan L, Dankovic D, Lentz TJ, MacMahon K, Kuempel E, Zumwalde R, Schulte P, on behalf of the NIOSH Carcinogen and RELs Policy Update Committee. Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 2017-100. DHHS (NIOSH) Publication No. 2017–100. 100.pdf?id=10.26616/NIOSHPUB2017100revised