Material Testing Requirements for OSHA PSM and
NFPA 652 Compliance
When conducting a risk evaluation in industrial operations, two factors must be considered: the potential consequences of a hazard and the likelihood or frequency of it occurring. If the calculated risk is unacceptable, measures must be taken either to reduce the severity of the hazard itself or to reduce the probability of occurrence.
In the United States, OSHA regulations and NFPA standards form the basis for this process. OSHA’s Process Safety Management (PSM) rule requires documented process hazard analyses, and NFPA standards such as NFPA 652 and the upcoming NFPA 660 specify the use of Dust Hazard Analyses (DHA). These frameworks require not only the identification of hazards but also the use of data to evaluate how those hazards behave under both normal and abnormal operating conditions.
Table of Contents
- Risk Assessments and Regulatory Framework in the US
- Hazard Identification: Inherent vs. Process-Generated Risks
- Thermodynamics, Kinetics, and Thermal Runaway
- Combustible Dust and Surface Area Effects
- Limitations of SDS and the Need for Testing
- Raw Material Changes and Process Safety
- Training and Fire/Explosion Awareness
- Integrating the Basis of Safety
- Process Laboratories Versus Specialized Testing
Risk Assessments and Regulatory Framework in the US
If a hazard is not identified, it cannot be evaluated or mitigated. This means no protective measures will be introduced because the risk was never recognized in the first place. Hazards may be inherent to a substance (e.g., flammable vapors or toxic solids) or they may be generated by process conditions.
For example, mixing incompatible chemicals can generate highly toxic byproducts such as chlorine gas. Under abnormal conditions, the hazards may increase or change altogether. A well-known example of this phenomenon is the Seveso incident in Italy, where a benign reaction sequence turned into an uncontrolled runaway, producing toxic dioxins due to elevated temperature and pressure. Although the system had explosion relief, the change in chemistry under excursion conditions was not anticipated.
Hazard Identification: Inherent vs. Process-Generated Risks
To prevent such oversights, the process industries use structured hazard identification methodologies such as HAZID, HAZOP, and LOPA. These methods require trained personnel who understand the process equipment, materials, and conditions involved. However, even the best analytical methods cannot always predict chemical behavior. In many cases, specific laboratory testing is required to characterize reaction pathways, ignition thresholds, and explosion severity.
Thermodynamics, Kinetics, and Thermal Runaway
Chemical reactions are governed by two principles: thermodynamics, which defines the energy changes associated with bond making and breaking, and kinetics, which describes how quickly reactions proceed. Exothermic reactions are particularly hazardous because they release heat exponentially, while most cooling systems dissipate heat linearly. If heat generation outpaces heat loss, temperature and pressure rise rapidly, leading to thermal runaway.
This risk is often underestimated at the laboratory scale. Glassware and small-volume vessels have high surface area-to-volume ratios and dissipate heat efficiently, which can mask the runaway potential of a reaction. At the industrial scale, the surface area-to-volume ratio decreases, heat dissipation slows, and any exothermicity is retained in the reaction mass. Once the rate of heat generation exceeds the rate of heat removal, runaway occurs, often with violent consequences.
Combustible Dust and Surface Area Effects
A similar principle applies to combustible dust. Combustion is an exothermic reaction between fuel and oxygen, and the kinetics of this reaction depend heavily on surface area. Bulk solids may not ignite, but when ground into fine powders, their reactivity increases dramatically.
For example, an iron bar does not burn, but iron filings ignite easily in a flame, and micronized iron powders can self-heat and ignite in air. These behaviors cannot be predicted by bulk properties alone and require standardized material testing.
Safety Data Sheets: Limitations and the Need for Testing
In the US, Safety Data Sheets (SDS) required by OSHA often provide only limited hazard information. A common statement is “this material may be combustible as a dust.” Such language is too vague to support safe design.
Engineers require quantitative values, including:
Minimum Ignition Energy (MIE)
Minimum Explosible Concentration (MEC)
Deflagration Index (Kst) and Maximum Pressure (Pmax)
Minimum and Layer Ignition Temperatures (MIT, LIT)
Resistivity and electrostatic charging properties
These parameters cannot be estimated; they must be measured in standardized tests such as ASTM E1226 (Go/No-Go, Kst, Pmax) and ASTM E2019 (MIE).
Industry often designs effective operating limits for normal conditions, but incidents occur when processes exceed those limits. Laboratory testing must therefore be integrated into risk assessments to evaluate both normal and abnormal scenarios.
Common client questions illustrate the issue:
“If our supplier changes, is the process still safe?”
“If the SDS only says ‘may be combustible,’ do we need more testing?”
“If our process excursions exceed limits, what actually happens inside the vessel?”
The answers depend on test data—not assumptions.
Raw Material Changes and Process Safety
When raw material suppliers change, the process is not automatically safe. Even if the equipment and procedures remain constant, variations in the raw material may introduce new hazards. Differences in particle size distribution, moisture content, impurity levels, or concentration can alter ignition sensitivity, reaction rates, and explosion severity. Even small deviations can negatively affect processing systems.
Any input change—whether in material specification, batch size, or operating parameters—has the potential to shift process behavior. A 10 °C increase in reaction temperature, for example, can approximately double the reaction rate. This acceleration may lead to thermal runaway or decomposition if the system was not designed to manage the increased heat and pressure. Similar risks arise from increased feed rates, altered solvent ratios, or scale-up operations.
For this reason, US facilities must apply Management of Change (MOC) procedures as required under OSHA’s Process Safety Management (PSM) rule. New raw materials should be characterized through laboratory testing to confirm whether existing controls remain adequate. Testing may include combustibility screening (Go/No-Go), ignition sensitivity, or calorimetry to evaluate thermal stability.
MOC evaluations should determine whether additional layers of protection are required—such as inerting, improved venting, or stricter temperature control. Importantly, testing must come before the implementation of mitigation measures so that controls are based on quantitative hazard data.
Test results provide the information needed to revise risk assessments and bring the process back to a safe operating state. Even if the change is limited to material sourcing, comparative testing is required to confirm that the new material behaves within the same hazard parameters as the previous supply. Without this verification, facilities risk operating under outdated assumptions about material behavior.
Training and Fire/Explosion Awareness
Having general fire and explosion awareness training is not sufficient for process industries. The key question is whether the entire workforce understands what could go wrong in their facility and how severe the consequences might be. Without that knowledge, training programs remain theoretical and do not prepare personnel for real plant hazards.
Generic fire extinguishing or evacuation drills cannot substitute for training tailored to actual process conditions. For example, attempting to suppress a jet fire with a handheld extinguisher is ineffective and potentially dangerous. Training must reflect the hazards specific to each site—whether those are combustible dusts, flammable vapors, exothermic reactions, or toxic gas releases.
If hazards have not been identified through risk assessments and material testing, they cannot be incorporated into training. Data such as minimum ignition energy, explosion pressure rise, or thermal decomposition onset provide the technical basis for credible training scenarios. Without this information, employees are being trained for hazards that may not match the reality of their process.
Effective training should extend beyond routine operations. Maintenance, startup, shutdown, and abnormal conditions all introduce different risks that require separate procedures. NFPA standards emphasize that training must account for non-routine operations, as these are often the conditions under which major incidents occur.
In US facilities, OSHA’s Process Safety Management (PSM) standard requires that operators be trained on the hazards of their processes and that refresher training be conducted regularly. This is not a box-checking exercise. It requires site-specific, data-driven content developed from actual hazard testing.
Ultimately, training programs must be built on a clear technical understanding of how materials behave under both normal and abnormal conditions. Only when hazards are identified and characterized can training be structured to prepare employees for credible fire, explosion, and toxic release scenarios.
Integrating the basis of safety
The basis of safety is not applied at the site level; it must be defined for each individual piece of process equipment. Every unit operation has different hazards, and therefore each requires its own technical justification.
For example, the basis of safety for a dust collector may be explosion venting, suppression, or containment. A screw conveyor may require ignition source avoidance, while a hammer mill may require a different combination of preventive and protective measures. Each operation must be evaluated on its own terms, and the chosen basis of safety must be technically defensible for the hazards present.
The basis of safety can be defined as the engineered precautions built into a process to prevent or mitigate harm. In practice, three broad approaches are available under NFPA standards:
Explosion Prevention – reducing concentration below the Minimum Explosible Concentration (MEC) or reducing oxygen below the Limiting Oxygen Concentration (LOC).
Avoidance of Ignition Sources – controlling electrostatics, sparks, frictional heating, and hot surfaces to keep energy inputs below the Minimum Ignition Energy (MIE) or Minimum Ignition Temperature (MIT).
Explosion Protection – designing venting, suppression, or containment systems to withstand or relieve overpressure if an explosion occurs.
Selecting the correct basis of safety requires an in-depth hazard assessment informed by material testing. Data such as Kst, Pmax, MEC, MIE, MIT, LIT, LOC, and Go/No-Go results provide the quantitative foundation for choosing whether prevention, ignition control, protection, or a combination of these strategies is the most appropriate.
NFPA 652 and the forthcoming NFPA 660 emphasize that combustible dust testing is required to establish the basis of safety for each unit operation. OSHA enforces these requirements under the General Duty Clause, citing facilities that fail to evaluate or justify their bases of safety with test data.
Ultimately, the basis of safety is an equipment-specific concept. It cannot be assumed or generalized across a facility. Each operation must be assessed with data-driven methods, and the chosen approach must be consistent with both the material properties and the process hazards identified.
Process Laboratories Versus Specialized Testing
Many company laboratories focus primarily on quality control testing—such as verifying product purity, composition, or flash point—rather than on process safety testing. While quality data is essential, it does not provide the information needed to evaluate fire, explosion, or reaction hazards. For process safety, engineers must understand not only whether a material is combustible but also:
How high the maximum explosion pressure (Pmax) can rise.
How quickly the pressure develops (Kst, rate of pressure rise).
At what temperature dust clouds or layers ignite (MIT, LIT).
How much energy is required for ignition (MIE).
The concentration limits at which dust clouds become explosible (MEC).
The oxygen concentration below which combustion cannot propagate (LOC).
These parameters cannot be estimated from bulk properties or standard quality tests. They must be measured using specialized laboratory equipment and standardized methods.
The reality is that most in-house laboratories are not equipped for this type of testing. Equipment such as 20-liter or 1-m³ explosion vessels, Hartmann tubes, and adiabatic calorimeters is highly specialized and expensive to maintain. Few facilities outside of dedicated process safety laboratories possess the capability to generate this data reliably.
Because of this limitation, most facilities rely on third-party laboratories that are accredited to recognized standards and capable of conducting ASTM, ISO, and UN-defined tests. The data produced by these tests is critical for completing risk assessments and establishing a defensible basis of safety.
Selecting among these approaches requires test data that reflects how materials actually behave under process conditions. Without laboratory testing, facilities are forced to design controls based on assumptions rather than measured values.
Conclusion
Effective risk assessments require quantitative data, not assumptions. Without laboratory testing, hazards remain unidentified, and protection systems are designed on guesswork rather than measured data.
OSHA’s PSM standard and NFPA frameworks such as NFPA 652 and NFPA 660 require hazard analyses supported by test data. Parameters like Go/No-Go explosibility, MIE, Kst, Pmax, and LOC form the foundation for DHA, PHA, and explosion protection design.
The most costly approach is reactive testing—waiting until after an incident. Proactive testing during process design or Management of Change ensures safeguards are based on verified behavior.
Sigma-HSE’s testing laboratory provides standardized testing of combustible dusts, gases, and reactive chemicals in accordance with ASTM, ISO, and OSHA-recognized methods. Our consulting team translates test results into actionable recommendations, integrates data into risk assessments, and helps facilities align with regulatory requirements.
When to contact us:
Before changing raw material suppliers
When SDS documents provide only generic hazard statements
During process scale-up or equipment modifications
When preparing for OSHA inspections or citations
If you’re uncertain about fire, explosion, or reaction characteristics
Contact Sigma-HSE to establish a data-driven foundation for process safety at your facility.
