Understanding Toxicity Levels and Protective Action Criteria

Toxic chemicals are different to most workplace hazards.

Where most hazards have an instant effect and can be impossible to miss (such as tripping over an errant wire or falling off scaffolding), toxic chemicals might have no immediate effect – even resulting in dermal contamination without the worker being aware of it.

Adding further complexity: there are thousands of chemicals in use globally (the Directory of Chemical Producers lists over 21,500), each with its own unique form and level of toxicity – along with unclear or limited knowledge about the possible long-term effects. And the long-term consequences can be catastrophic: cancers, organ damage, fertility effects, and so on. Toxic chemicals present a perfect storm for the EHS professional navigating worker protection.

“Toxicity” can be defined as the volume or concentration of contamination that is likely to cause harm. In all of this uncertainty, one thing that is clear: while many chemicals have relatively low toxicity levels, many are highly toxic. In other words, small amounts can be harmful.

Choosing PPE for Toxic Chemicals

Combine this with a simple fact that is both unnerving and unavoidable: the most popular chemical suit configuration for workers around the world is a coverall with hood. Such PPE combinations do not provide a full seal against leakage. Even when combined with other PPE, such as face-mask and gloves, a low level of inward leakage inside the suit is almost inevitable, especially with chemicals that vaporize easily at normal temperatures. The only sure way of avoiding this is to wear a fully gas-tight suit, which is often beyond the budget of many businesses.

For this reason, it is important for safety professionals tasked with choosing chemical protective clothing for workers have the resources to understand both the level of chemical contamination that might cause harm (the “toxicity level” or “TL”), and how much of the chemical might get inside a suit over time (the inward leakage). With this knowledge a safe-wear time, the maximum time a worker should remain with potential exposure, can be calculated.

So, when conducting a risk assessment, what information is available that indicates the toxicity levels of different chemicals?

The Development of Protective Action Criteria

This question faced the U.S. Office of Emergency Management, part of the U.S. Department of Energy, when developing support for organizations planning to respond to the uncontrolled release of hazardous chemicals. This was part of a development related to the National Nuclear Security Administration.

The answer came in the form of Protective Action Criteria, or PACs. Originally developed in the 1980’s, this takes the form of an open database of over 3,000 chemicals defining the volume per meter cubed (mg/m3) or concentration in parts per million (ppm) that may cause different levels of harm:

PAC 1: The level that could result in only transient or temporary effects
PAC 2: The level that could result in permanent effects
PAC 3: The level that could result in fatality

How Are PACs Used?

On their own, PACs are of limited use in determining appropriate chemical protective clothing, but they do provide guidance on the relative toxicity of chemicals and enable professionals to create response plans for incidents involving hazardous chemical release. They are now widely used throughout the U.S. by a range of security and civil defense organizations. For example, the Office of Response and Restoration uses PACs to define different threat zones in the event of hazardous chemical release.

The DEO handbook for methods and practice of emergency exposure limits describes the essential components of managing incident response:

• The chemical identity
• The amount released
• The concentration
• The duration of exposure
• The characteristics of the population exposed
• Circumstances affecting exposure such as wind strength and direction, temperature, etc.

Similarly, effective management of exposure to toxic chemicals in the workplace, along with selection and management of appropriate PPE, requires essential information:

• The chemical identity
• Its toxicity – how much is required to cause harm
• The likely level of exposure (in chemical suit terms, how much is likely to get inside the suit, either via permeation through fabric or penetration through gaps with other PPE worn)
• Any other influencing factors, such as temperature, which can affect both permeation and vaporization

Using this information it is possible to calculate Safe-Wear Times – the maximum time a worker should remain with exposure to the chemical in a specific chemical suit. The challenge is obtaining the information, toxicity levels, likely inward leakage and the effect of factors such as temperature.

The PermaSURE Solution

PermaSURE is a tool used by Lakeland Fire + Safety to provide our chemical suit users with detailed information on safe-wear times, information related to the chemical and how long it can be safely worn according to the specific application conditions.

So while PACs are of limited value to users for direct identification of the right chemical suit, they provide key data used for PermaSURE to help determine safe-wear times, the maximum time a wearer should remain with potential exposure. This provides safety managers with a realistic guide to task management where toxic chemicals are a hazard, enabling workers to remain safe with greater certainty than is otherwise possible.

PACs are developed using a specific hierarchy of data. To learn more detail about these sources read on below.

More Information on Protective Action Criteria

PACs, the source for the toxicity limits used in PermaSURE, have been developed from a hierarchy of three key data sources:

• AEGLs (Acute Exposure Guideline Levels)
• ERPGs (Emergency Response Planning Guidelines)
• TEELs (Temporary Emergency Exposure Limits)

Each of these datasets identifies three similar tiers of toxic thresholds: –

• Tier 1: Temporary, non-disabling effects
• Tier 2: Disabling (escape impairment) or permanent effects
• Tier 3: Life-threatening effects threshold

In some cases, a chemical will have thresholds in two or more of the three datasets, and not always the same. So, how are such conflicts resolved in order to create a combined database?

The answer is to select data from each according to its relative known effectiveness, based on its source and how it is assembled.

AEGLs are the most accurate source of toxicity data. They are produced by the US Environmental Protection Agency and are based on solid, peer reviewed, experimental data for the general population and including sensitive individuals. As of the update in 2018, some 185 chemicals had confirmed AEGLs, another 71 had interim AEGLs and a further 14 had proposed or “holding” AEGLs.

ERGPs are considered the next most effective. These are produced by the American Industrial Hygiene Association and are compiled for a range of source data. At the last update in 2022 some 145 chemicals had EGRP’s.

You can learn more about ERPG’s here

Most commonly used chemicals are covered in the lists of AEGLs and ERPGs. However, recognizing that the list is somewhat limited. A third source of data, TEELs has been developed by  SCAPA, (the Subcommittee on Consequence Assessment and Protective Actions), part of the US Department of Energy.

TEELs are assembled from a methodology using existing data rather than specific studies (as is the case with AEGLs and ERGPs) so are considered inferior to the other two, but still provide useful data-based toxicity information. You can learn more about the development and use of TEELs in the DOE guidebook here.

In a judgement based on the way the toxicity data is produced, AEGLs comprise the best available data, ERGPs the second best, and TEELs the third. Given that some chemicals are replicated in two or more of these sources, and not always with the same values, to combine these three into one, the PAC database is compiled using the following rules:

1. For chemicals for which there ERPGs are available, those values are used.
2. If no ERPG values are available, AEGLs are used where they are.
3. If neither ERPG nor AEGL values are available, TEEL’s are used

So, in effect, the PAC database, the essential data used in the PermaSURE tool as the basis for assessment of chemical toxicity and safe-wear times, combines all three of these sources into one, so represents the best available database of knowledge the chemical toxicity of over 3,000 chemicals.

Our PermaSURE safe-wear time assessment tool provides users with detailed information on safe-wear times for our chemical suits based on the parameters of a specific application and using toxicity data based on the PAC database values.