Combustible Dust and Its Hazard (Explosion Protection Design)

Important Considerations

The design for explosion protection must incorporate at least one of these methods:

      I.        Reduction in the oxidant concentration

    II.        Dilution with non-combustible dust

   III.        -Deflagration Control by ventilation, pressure containment, suppression or devices for flame suppression and containment. 

            Any part of the structure that is designed to relieve pressure during an explosion should be located and constructed so that it poses no accident risk while in use

The most common explosion control mechanisms are:

·         Confinement or containment,

·         Inerting

·         Isolation, suppression or deflagration release

Processing Equipment that generates combustible dust must be connected to a dust collection system. This system usually consists of a structure that conveys the dust through pipelines from the point where it is generated to the final collection point known as a dust collector. Dust can be transported through the system via mechanical energy (conveyor), or pneumatic (air). The NFPA 654, includes as collection and material handling equipment, systems for material transfer, pipelines, power machinery equipment, separators, conveyors, mixers, dryers and more.

Dust collectors must be equipped with safety devices that prevent or minimize the risk of

an explosion during normal operation, as established by NFPA 654

Filter systems for dust collectors cannot be replaced by alternative type systems unless

a complete fire risk assessment is performed and it has been properly documented and

approved by management.

It is recommended that whenever possible, locate bucket elevators outside the building.

For systems that handle metal particulate is necessary to classify the material as:

·         water, compatible

·         non- compatible with water, and

·         water-reactive,

to determine the fire protection system appropriate to the material properties.

Walls and  internal partitions construction in areas where combustible dust is present, 

usually require a minimum fire resistance protection of at least 1hr.

If the material transfer equipment is used for various products you must verify the

compatibility between products prior to using the equipment.

It is of upmost importance to always keep the horizontal surfaces and work area clean of

material accumulation.

In the event that some areas are difficult to reach or cannot be easily cleaned, the

recommendation is to completely seal them off.

The initial and refresher training to employees should include the area hazards, process

description, procedures, equipment, fire and explosion protection systems,

maintenance requirements, cleaning and emergency response plans.

The equipment maintenance includes frequent inspections to detect and remove product accumulation in critical areas. 

APPENDIX A – OSHA STANDARDS

What standards or guidelines are available?

OSHA (Occupational Safety and Health Administration)

Currently there is under approval process an OSHA standard that would cover industrial operations where combustible dusts are present. Although there is still no comprehensive standard for all operations that handle combustible dusts, several OSHA standards indicate certain key provisions for the control of risks associated with the handling of combustible dust in industrial operations. The standards discussed in this section are mandatory according to the type of industry applicable to your particular operation.

1910.22 - General Requirements (see Housekeeping)

1910.22 (a) (1) All places of employment, passageways, storage areas and service should be kept clean, in order and hygienic.

1910.22 (a) (2) the floor of each work area must be kept clean and kept dry as much as possible.

Since these are general requirements, they apply to all general industry operations covered by the Code of Federal Regulations (CFR) 29.1910

1910.38 - Emergency Action Plans

1910.39 - Fire Prevention Plans

1910.157 - Portable Fire Extinguishers

1910.165 - Employee alarm systems

These standards require employers to establish emergency action plans, including fire’ indicate the minimum necessary procedures to respond to emergencies, the equipment requirements for fire prevention and training requirements for personnel

1910.94 – Ventilation

Related to abrasive blasting systems,  the standard indicates that if flammable or explosive mixtures of dust are present, the work area must be constructed to provide secure mechanisms to release pressure in case of explosion. It incorporates by reference the NFPA 68 the requirements for the area construction and for security mechanisms.

1910.119 - Process Safety Management (PSM)

The purpose of this standard is to prevent or reduce the catastrophic consequences that arise from the handling of highly hazardous materials processes. The applicability of the standard depends on the type of material and the amount of material used in the process. Refer to Appendix A for a list of materials covered under the standard.

1910.132 - Personal Protective Equipment

The facility must have implemented the program including a risk analysis of each task for the selection of the equipment. Clothing and accessories for use in areas where combustible dust is present must include fire-resistant clothing and electrically rated footwear.

1910.176 - Material Handling and Storage

This standard generally covers the basic requirements for proper handling of materials. Section 1910.176 c) specifies that storage areas be kept free of accumulation of material that may cause danger of falling, tripping, fire, explosion or pests.

1910.178 - Industrial Forklifts

Table N-1 of the standard defines what kind of truck is suitable for use in handling and transportation of combustible dusts for Class II, Groups E, F, G. The type of forklift is identified by letters indicating which fuel or energy is used to operate the motor, and the equipment safety devices.

 For areas Class II, Groups E and F where combustible dust is present, the only trucks approved are those designated as EE or EX. For the Group G the approved designation will be only GS, LPS, DS, DY, ES, EE, or EX. All these designations provide mechanisms to prevent that electrical or combustion systems of the equipment enter unwanted ignition sources in areas where dust are present.

1910.263 - Bakery Equipment

Section 1910.263 (k) identifies the electrical safety requirements for equipment used to pulverize sugar and / or spices and section 1910.263 (l) establishes requirements for equipment / mechanisms to release pressure in case of explosion.

1910.265 - Sawmills Operations

The standard applies to sawmill operations such as, logging, handling, cutting, sanding, handling and storage of timber or related products. Establishes requirements to prevent fire or explosion of dust collection equipment, electrical protection for certain equipment and also minimum cleaning frequency requirements of the work area

1910.272 - Grain Handling Facilities

This was the first standard written specifically to control risks associated with grain handling, classified as combustible dust. It is aimed primarily at grain handling operations for the food industry and specifies the procedures, equipment 

requirements and safe work practices for that type of operation. Typically, the silos are considered confined spaces and therefore must also refer to Standard 1910.146 - Confined Spaces for safety considerations when working in silos or similar spaces.

1910.307 - Hazardous Locations

This standard defines  the requirements for electrical equipment and wiring to be used in electrically classified areas based on the properties of flammable liquids, solids or gases, combustible dusts and / or flammable fibers present in that area.  It references the NFPA 70 standard.

1910.1200 - Hazard Communication

This standard requires besides the identification of health hazards, the physical hazards present in the work area including but not limited combustible dusts. Each employer is responsible for obtaining the information about the safe handling of these materials and providing such information to  their employees through signs, labels, notices. The employer must provide training related to the handling and proper use of the material as well as ways to protect employees from the hazards associated with particular material.