Fire Codes and the GHS

Part 4: Toxicity – inhalation exposure route

In Part 4 of our series, highlighting the differences between the IFC hazard classes and the GHS, we’re picking up where we left off, comparing IFC and GHS toxicity hazard classes, this time for gas, vapor, dust, fumes and mist via inhalation. The goal is to help code users confidently assign the applicable fire code hazard class when the GHS hazard classes, generally available in a material’s Safety Data Sheet, are known.

Background

OSHA’s Hazard Communication (HAZCOM) Standard (29 CFR 1910.1200) prescribes the hazard classification system manufacturers are required to use to classify and label chemicals and communicate the hazards of materials in Safety Data Sheets (SDS). Appendix Table E104.2, introduced in the 2024 IFC, presents IFC hazard classes alongside those found in HAZCOM 2012, based on Revision 3 of the GHS. A much-awaited update to the HAZCOM Standard, based on Rev. 7 (2017) and some elements of Rev. 8 of the GHS, was finalized on May 20, 2024, and takes effect on July 19, 2024.

This article compares the IFC’s highly toxic and toxic gas hazard classes with the GHS (Rev. 7) classifications to identify where OSHA HAZCOM (2024) differs. If you’re using the NFPA 1 Fire Code, this comparison will be helpful to you, too, because the toxicity hazard classes defined in NFPA 1 and the IFC align.

Fundamental Concepts

Before delving into comparing specific hazard classes, reviewing some relevant and fundamental toxicity-related concepts is crucial. This understanding will prepare you for the in-depth comparison that follows.

Acute vs. Chronic Effects

Acute effects occur after a single exposure or a few exposures to a substance and can happen immediately or within hours or days.

Chronic effects develop after prolonged exposure to a substance over months or years and typically have a delayed onset.

The Lethal Concentration (dose)

Since the lungs offer a direct path to the bloodstream, inhaling toxic substances can quickly become deadly. The Lethal Concentration 50 (LC50) measures how much of a substance needs to be continuously inhaled by test animals to kill half of them during a single exposure. Typical test exposure times are 1 or 4 hours, and a lower LC50 indicates higher toxicity.

The IFC uses LC50 values to express a material’s acute toxicity, and the test methods determine LC50 values directly. However, the GHS uses acute toxicity estimates (ATE) derived from LC50s or newer study methods (e.g., use of fewer animals) and other indicators of acute toxicity, such as significant clinical signs in humans, to estimate acute toxicity.

When defining highly toxic and toxic via inhalation, the IFC considers the inhalation of gases, vapors, mists, fumes, and dust, and the LC50 units depend on the substance’s form.

Gases and vapors: Parts of substance per million parts of air by volume (ppm)
Dust, fumes, and mists: Milligrams of substance per liter of air (mg/L)

The GHS uses these same units but does not explicitly address fumes.

Gas, vapor, dust, fume, or mist?

Unlike other hazard classes, knowing the form of a substance is necessary to accurately crosswalk between the IFC and GHS toxicity via inhalation hazard classes. The manufacturer may or may not provide the form as part of the hazard class, and you may not find it in the ‘Toxicological Information’ provided in Section 11 of the SDS. So, a basic understanding of the differences between gas, vapor, dust, fume, and mist is helpful in cases where you may need judgment to establish the classification.

The IFC doesn’t define these terms, and Merriam-Webster’s Collegiate Dictionary, 11th Edition, only provides minimal context, so these descriptions might help you better understand the differences.

Gases are substances entirely in a gaseous state at normal temperatures and pressures.
Vapors are a gaseousform of a substance or mixture released from its liquid or solid state.
Dusts are solid particles of a substance or mixture suspended in a gas (usually air).
Fumes are finely divided solid particles formed by condensing vapors from a solid material, like metal or plastic, during processes like welding or heating.
Mists are liquid droplets of a substance or mixture suspended in a gas (usually air).

I’ve also seen LC50s listed on SDSs for substances in aerosol form, typically when the material is a liquid used in a spray application, like liquid fertilizers, not in an aerosol container. Even though the IFC doesn’t define or address aerosols as ‘hazardous materials’ per se, I’m providing a description should you encounter this term, as I did. I treat these as mists when the base product is a liquid in other than an aerosol container.

Aerosols are a suspension of particles or droplets in air. Aerosols may include airborne dust, mists, fumes, or smoke.

GHS & HAZCOM

GHS (Rev 7) Table 3.1.1 below shows how ATE values are categorized based on the inhalation route of exposure for each form (gas, vapor, dust, and mist) under the GHS classification system. OSHA HAZCOM classifies toxicity similarly, except it does not include Category 5. Both GHS and HAZCOM use ATE values based on a 4-hour exposure time.

If the LC50 data for a product is not made available in Section 11 of the SDS, there are other sources of acute toxicity data, mainly for pure materials. Appendix B of Application of Modern Toxicology Approaches for Predicting Acute Toxicity for Chemical Defense¹ provides a particularly good summary of available toxicity data and databases.

IFC/IBC

The 2024 IFC and prior editions rely on LC50 data to establish whether a material should be classified as highly toxic or toxic. LC50 values for the inhalation route, based on the substance form and a 1-hour exposure time.

The Deep Dive

Note that the LC50 values for acute toxicity under the IFC consider a 1-hour test exposure, but the GHS relies on a 4-hour test time. In addition, the IFC expresses LC50 units for vapors in parts per million (ppm), while the GHS uses milligrams per liter (mg/l). That means we need to make several conversions to ensure we’re comparing apples to apples.

Regardless of the substance form, there’s a straightforward conversion formula to adjust for the difference in toxicity test exposure times.

For vapors, both the exposure time and units need converting. While ppm is a volume-to-volume or mass-to-mass ratio, mg/l is a mass-to-volume relationship. The U.S. Environmental Protection Agency’s (EPA) Risk Management Program offers guidance on this conversion.

The formula shows that the molecular weight of the substance or mixture is needed, which means we’ll have to estimate the toxic category (ppm) endpoints for vapors in our GHS/IFC comparison. Estimation data is available on request.

Our deep dive comparing the GHS hazard categories and IFC hazard classes for Acute Toxicity (Inhalation) reveals the following:

You can find the LC50 or ATE data for a material in Section 11 of the SDS supplied by the manufacturer. An often-misunderstood concept is the data needed to classify mixtures must reflect the whole mix. Although there are ways to calculate and estimate LC50s for mixtures using toxicity data for each hazardous component, the LC50 or ATE data for the mixture should also be available in the SDS.

IFC Appendix Table E104.2

Referring to the new IFC Appendix Table E104.2 in the 2024 IFC, similar GHS Acute toxicity Categories are identified for the IFC Toxic and Highly Toxic hazard classes. Unfortunately, the Appendix Table doesn’t offer the details we just examined. While the Table is a valuable resource, the code user must still analyze each definition to uncover where inconsistencies might exist.

Key Takeaways

OSHA recently updated its HAZCOM Standard, requiring chemical manufacturers to update the hazard classifications in their Safety Data Sheets (SDSs) to align with GHS Rev. 7 and some Rev. 8 classifications.
2024 IFC Table E104.2 can help you navigate between the GHS/OSHA hazard classifications in Section 2.1 of SDSs and IFC hazard classes. However, close evaluation is required to find the nuances between the IFC hazard class and GHS definitions in the Table. The differences are not red flagged.
The comparison table below simplifies the findings from the deep dive above for acute toxicity for the inhalation route of exposure. When you know the GHS acute toxicity hazard classes, refer to this Comparison Table to help decide if a material is highly toxic or toxic under the IFC.

Footnotes:

¹Committee on Predictive-Toxicology Approaches for Military Assessments of Acute Exposures; Committee on Toxicology; Board on Environmental Studies and Toxicology; Board on Life Sciences; Division on Earth and Life Studies; The National Academies of Sciences, Engineering, and Medicine. Washington (DC): National Academies Press; 2015 Sep 1.