DEKRA Process Safety

A Filter/Receiver Dust Explosion

filter/receiver dust explosion

A filter/receiver directly connected to a powder milling operation exploded giving rise to an indoor deflagration, which, fueled by powder deposits, propagated into three floors of the facility. Fortunately no one was injured, however, the filter/receiver was destroyed by the explosion and several other pieces of equipment were damaged by fire. Windows were blown into a courtyard from three floors of the building. A deflagration in the courtyard caused damage to several building windows.

A mill bearing failure caused overheating of the powder and creation of embers, which entered the filter/receiver and initiated a primary dust/air explosion. Dust accumulations in the explosion relief discharge ductwork caused delayed activation of the relief door and over pressurization of the filter/receiver. Poor housekeeping had allowed significant dust accumulations on floors and overhead surfaces.
The root cause of this incident was “less-than-adequate recognition of dust explosion hazards (Dust Hazard Analysis)” including:

  • Less than adequate housekeeping (Management Systems),
  • Less than adequate preventive maintenance of rotating equipment (Mechanical Integrity),
  • Less than adequate monitoring of mills (DHA),
  • Less than adequate explosion relief system and system maintenance (Mechanical Integrity

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Are You Using the Right Hose for Combustible Dust Vacuuming Applications?

using the right hose for combustible dust vacuuming

Why Is It Important?

Significant electrostatic charge can be generated where nonconductive hoses are used for vacuuming applications. The development of electrostatic charge can lead to various types of electrostatic discharge inside of the hose. If the solid particulate being vacuumed is combustible in nature, the discharge can ignite a dense dust cloud inside of the hose, in situations where thick layers or piles of dust are being vacuumed, causing a deflagration.

What Properties Should my Hose Have?

The National Fire Protection Association (NFPA) standards provide guidance with regard to properties of hoses used for vacuuming applications. A suitably conductive or antistatic hose will demonstrate one of the following properties: (1) An end-to-end resistance, not to exceed 108 ohm (100 megohms); (2) A liner Surface Resistivity less than 109 ohm/square, as measured by [1] ASTM D256 test or (inner liner) charge relaxation time less than one (1) second. Note: the latter two properties must be measured in a laboratory using the appropriate test conditions. Hoses incorporating metal wires for reinforcement must be connected so that the wires are bonded to the conductive components on each side of the hose connection and then grounded.

A Common Misconception

The hose I am using has metal reinforcing wires extruded in the liner and I have bonded the wire on both ends to the conductive tool in the hard pipe or conductive inlet to the portable vacuum cleaner so there is no danger of charge build up. Fact: If the construction material of the hose is nonconductive, charge can build up on the inside surface of the hose and lead to development of a propagating brush discharge of sufficient energy to ignite a combustible dust flowing inside the hose. The presence of the conductive wire may enhance this possibility.

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Are You Protecting Your Personnel and Processes Before Bringing New and Updated Equipment and Processes Online?

pre-startup safety review

The Occupational Safety and Health Administration (OSHA) implemented the Process Safety Management (PSM) program in 1992. One of the more critical elements of OSHA PSM program in 29 CFR (Code of Federal Regulations) 1910.119, under subpart (i) is Pre-Startup Safety Reviews (PSSR). This critical element according to OSHA PSM states:

1910.119(i) Pre- startup safety review
1910.119(i)(1) The employer shall perform a pre-startup safety review for new facilities and for modified facilities when the modification is significant enough to require a change in the process safety information
1910.119(i)(2) The pre- startup safety review shall confirm that prior to the introduction of highly hazardous chemicals to a process
1910.119(i)(2)(i) Construction and equipment is in accordance with design specifications
1910.119(i)(2)(ii) Safety, operating, maintenance, and emergency procedures are in place and are adequate
1910.119(i)(2)(iii) For new facilities, a process hazard analysis has been performed and recommendations have been resolved or implemented before startup; and modified facilities meet the requirements contained in management of change, paragraph (l)
1910.119(i)(2)(iv) Training of each employee involved in operating a process has been completed

The PSSR process is the last line of defense before bringing an updated or new process online to ensure that it has been properly designed, all the equipment and process information is complete and available, the equipment is installed per the design specifications, a PHA has been conducted and all recommendations are completed (for new or changed processes) all safety, operating, maintenance and emergency procedures are adequate and complete, and all training of operation personnel is completed. The one item that is not specifically spelled out in this regulation, but is probably included in the equipment is the digital control system (DCS) and/or safety instrumented system (SIS). This system assists the operators in running and controlling parameters such as the material flow, temperatures, pressures, and levels within the process. It also provides alarms to alert operators if the process is starting to get out of control and interlocks to take certain actions, intervene or even stop the process, if necessary. Too often, taking the time to ensure all the automated valves, associated process instrumentation, and alarms and interlocks are active and functioning properly before starting a new or updated process or restarting the process after a major shutdown is ignored or overlooked.

In the BP incident on March 5th, 2005, which killed 15 and injured 170+ others, safety critical checks were not properly conducted, as the incident investigation found that an inoperative pressure control valve, a defective high level alarm, and a defective sight tower-level transmitter had not been calibrated and portable trailers with non-essential personnel were located too close to the process. In two other incidents, where improperly conducted PSSRs of the process controls settings and systems settings caused no deaths or injuries, but still damaged process and equipment and had a financial and business impact were: (1) Equipment which was manufactured in Europe and shipped to the US, a 50 Hz motor setting remaining from preliminary testing overseas (should have been changed and set to 60 Hz for US operations) caused a motor to run slower and resulted in a process shut down due to high temperature. While cooling the process, other operational steps were taken and the end result was a propagating fireball explosion which caused extensive damaged to the outdoor process equipment and some siding on the building. (2) Another incident in a manufacturing operation involved the replacement of a circuit board, supposedly like in kind, but actually the updated newer version. No PSSR was conducted and several critical interlocks were not operational due to the board replacement. End result was damaged shaft, repair and replacement cost, and the associated lost production time (8-10 weeks).

In all of these incidents properly conduct PSSRs with checks of the DCS/SIS system and operation of the automated valves, instrumentation, alarms, and interlocks before commissioning/starting the equipment, bringing the equipment back online after an outage or replacement of parts would have probably prevented these incidents. It takes both trained and qualified employees and knowledgeable and informed safety-minded management to ensure that PSSRs are thoroughly conducted and approved before allowing processes to be brought online or restarted to avoid these incidents.

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The Dangers of Using Dust Explosion Data from “Public” Sources

pre-startup safety review

When assessing the fire and explosion hazards of powders and powder processing operations in a facility, there is often an inclination to first search for data from publicly available sources. While data obtained from public sources could offer some general insight regarding the ease of ignition and severity of the resulting explosion for a powder, such data should not be relied upon for the assessment of the hazards of a powder. More importantly, such data must not be used for the design of fire and explosion prevention and protection measures for an operation, process equipment, or facility.

There are several factors that could greatly affect the ignition sensitivity and explosion severity properties of powders, including chemical composition, particle size, moisture content, and the laboratory test method. Public sources very often do not provide this essential information. For example, public sources for Kst and Pmax data often do not indicate whether the quoted values have been obtained utilizing a 1-Liter Hartmann Bomb, a 20-Liter sphere, or a 1m3 spherical vessel, nor is crucial information on particle size and moisture content of the powder sample generally provided. Reliance on literature data could result in underestimating the ignition sensitivity and explosion severity of a powder, with disastrous results.

Taking a representative dust sample from the facility or process equipment and conducting the required testing using the appropriate test standard at a qualified laboratory would provide the highest level of certainty in the data.

diagram showing increasing level of confidence in dust explosion data

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International Fire Code (IFC) Requires Compliance with NFPA 652

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Fire code official shall be authorized to order a Dust Hazard Analysis (DHA)

The 2018 edition of the International Fire Code (IFC) requires the owner or operator of a facility with operations that manufacture, process, blend, convey, repackage, generate or handle potentially combustible dust or combustible particulate solids to comply with the provisions of NFPA 652, Standard on the Fundamentals of Combustible Dust. The IFC has been adapted or is in use by 42 States, District of Colombia, New York City, Guam, and Puerto Rico.

According to Chapter 22 of IFC (2018), the requirements of NFPA 652 apply to all new and existing facilities and operations with combustible dust hazard. Existing facilities shall have a Dust Hazard Analysis (DHA) completed in accordance with the timetables contained in Section 7.1.2 of NFPA 652. The fire code official shall be authorized to order a Dust Hazard Analysis to occur sooner if a combustible dust hazard has been identified in a facility that has not previously performed an analysis.

IFC (2018) maintains existing requirements that prohibit smoking, the use of heating or other devices employing an open flame, or the use of spark-producing equipment in areas where combustible dust is generated, stored, manufactured, processed or handled. Further, the accumulation of combustible dust inside buildings is significantly limited. Accumulated combustible dust shall be collected by vacuum cleaning or other means that will not place combustible dust into suspension in air. Pressurized air shall not be used to remove dust from surfaces.

NFPA 652: Standard on Fundamentals of Combustible Dust

NFPA 652 was first published in September 2015 and provides general requirements for management of combustible dust fire and explosion hazards and directs the user to appropriate NFPA industry or commodity-specific combustible dust standards. It also establishes relationship and hierarchy with industry or commodity-specific standards, ensuring that fundamental requirements are addressed consistently across industries, processes, and dust types.

NFPA 652 requires the owner/operator of any facility with potentially combustible dust to take the following steps:

  • Determine combustibility and explosibility hazards of materials. Absence of previous incidents shall not be used as basis for deeming a particulate non-combustible or non-explosible.
  • Conduct a Dust Hazard Analysis (DHA) - Identifying and assessing fire, flash fire, and explosion hazards by an expert with demonstrated ability to deal with hazards related to processing and managing combustible particulate solids.
  • Manage identified fire, flash fire, and explosion hazards by considering the prescriptive requirements of NFPA 652. Alternatively, performance based options exist to evaluate ignition source control, as well as the level of design/protection features for the building and the equipment.
  • Establish written safety management systems for preventing or mitigating fires, deflagrations, and explosions. Written management system requirements shall apply to new and existing facilities and processes.

How Can We Help You Achieve Compliance with IFC and NFPA 652 Requirements?

DEKRA Process Safety helps process industries avoid major fire, explosion, and loss of containment events and improve their performance. Combining specialist process safety engineering and management expertise, with generation and use of process safety test data allows us to help clients achieve the most effective and practical approaches to safe and efficient operations and processes. With consulting offices and accredited state-of-the-art laboratories throughout North America, Europe, and Asia, Chilworth serves clients globally throughout the agrochemical, chemical, engineering, food and beverage, government, insurances/legal, metals, oil & gas, pharmaceutical, plastics, pulp & paper, rubber, wood and other industries.

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Laboratory Testing

lab testing

We operate one of DEKRA's world premier chemical process hazards laboratories. Process safety testing is used to develop the data on which fire and explosion hazard assessments and incident investigations should be based.

Learn about our Laboratory Testing options