Quiz: Dust Hazard Analysis (DHA)

December 10, 2025

Quiz: Dust Hazard Analysis (DHA)

Dust hazard analysis is a core requirement in NFPA’s combustible dust standards, but many facilities still struggle to spot gaps in their programs. This 10‑question quiz is designed to test your understanding of DHA fundamentals, from explosible dust properties to secondary explosion risks and mitigation strategies.

Use it as a quick self-check or share it with your team to test knowledge and spot areas to learn more

Quiz – Dust Hazard Analysis (DHA)

Think you understand combustible dust risks?

Take our 10-question Dust Hazard Analysis Quiz and test your knowledge of dust explosibility properties, ignition sources, credible scenarios, accumulation hazards, and the safeguards used to reduce deflagration risk.

1 / 10

Which of the following materials would most clearly trigger the need to perform a DHA under NFPA combustible dust standards?

Wet slurry with no potential to dry

Coarse gravel with a maximum size of 5 mm

Fine organic powder that can become airborne during conveying and handling

Large metal turnings from machining

2 / 10

In evaluating fugitive dust in a DHA, which factor is most critical for determining whether accumulated layers present a deflagration or flash-fire hazard?

Dust color

Dust layer thickness and coverage area relative to NFPA housekeeping criteria

Origin of the dust (raw material vs. product)

Dust vendor or supplier

3 / 10

In a DHA, which scenario most clearly represents a potential flash-fire hazard rather than just a housekeeping issue?

Thin dust layers limited to a single, small equipment base

Dust layers over a large floor area that can become suspended by a process upset or manual cleaning

Dust confined inside sealed containers only

Dust accumulation exclusively inside HEPA filters

4 / 10

What is the primary purpose of performing Hazardous Area Classification (HAC) during a DHA?

To assign electrical equipment maintenance schedules

To define the extent of areas where combustible dust atmospheres may form

To determine maximum storage capacity in silos

To calculate firewater demand

5 / 10

In a DHA, what does the presence of classified areas (e.g., Class II, Division 1 or 2) primarily indicate?

Areas with high electrical conductivity

Locations where combustible dust layers will always be present

Areas where combustible dust may be suspended in air under normal or abnormal conditions

Areas restricted to personnel entry

6 / 10

Which combination of factors must be present for a dust deflagration hazard to exist in a process area, as evaluated in a DHA?

Combustible dust, oxidizing atmosphere, and credible ignition source

Combustible dust, oxidizing atmosphere, credible ignition source, dispersion as a dust cloud, and some degree of confinement

Combustible dust and oxidizing atmosphere only

Confinement and credible ignition source only

7 / 10

When a DHA identifies that a dust collector handling combustible dust is located indoors without appropriate explosion protection, which action is most consistent with NFPA principles?

Do nothing if there has been no historical incident

Increase housekeeping frequency only

Provide a suitable explosion protection strategy, such as venting to a safe location, suppression, or containment

Replace the dust collector with a larger unit

8 / 10

Which condition most strongly influences whether a dust layer contributes to secondary explosion potential during an upset?

Whether the dust is organic or inorganic

Whether the layer can be mechanically or pneumatically disturbed and reach a concentration above the MEC

The color of the dust

The percent solids in upstream processes

9 / 10

When using Kst data in a DHA for a dust already known to be explosible, which statement is most accurate?

Kst determines whether a dust is combustible or not

Kst indicates how severe a dust cloud explosion could be; a Kst of 0 bar·m/s corresponds to St 0 (no explosion observed in testing), while higher Kst values place the dust into St 1–St 3 classes that reflect increasingly violent explosion behavior that may require stronger safeguards

Kst values are used to determine the minimum explosible concentration (MEC) of the dust

Kst is mainly used to decide whether dust housekeeping is required or not

10 / 10

How does NFPA 660 affect DHA requirements that were originally defined in NFPA 652?

It eliminates the need for DHAs in existing facilities

It consolidates and carries forward DHA requirements, including periodic revalidation, into a single comprehensive combustible dust standard

It replaces DHA with traditional HAZOP-style studies only

It limits DHA requirements to new facilities constructed after 2024