Managing Dusty Environments In The Food And Pharmaceutical Industry

Introduction On Basic Air Quality In A Food and Pharmaceutical Environment

Air quality is of paramount importance to the food, biotechnology and pharmaceutical industry. This is primarily for the protection of the product and the employees that work in these particular environments. 

Many food and pharmaceutical products are made in environments where the quality of air is of the utmost importance. Environmental air as it is often described has a particular quality defined by its temperature, humidity, levels of particle concentration and the extent of microbiological presence. In some cases, the air used must be completely sterile and free of any microbiological hazards including allergens and also such that no particulates of any sort must be present. If air is part of the manufacturing process for example, it must be controlled to within specific limits set out by governmental regulations.

Working in a dusty environment brings its own issues. The element relating to ‘levels of particle concentration’ in that definition of environmental air is almost as critical to manage as keeping air free of microbes. When working in dusty environments where dust from food, ingredients and excipients must be extracted, there is a significant explosion risk. Not only are people killed but infrastructures destroyed which can have even more serious consequences for people and environment! 

The other aspect which has a significant bearing concerns health due to particle inhalation. Air filtration is the main approach to reducing dust particles in air to prevent inhalation as well as product contamination. If the dust in the environment is uncontrolled, workers are required to wear dust masks for example. Otherwise, breathing in dusts leaves them prone to asthma and in cases where asbestos is present, prone to lung cancer.

In brief, controlling air quality is through manipulation of a number of factors such as: particle concentration using filters, the use of dehumidifiers or misters to regulate humidity and heaters or coolers to regulate temperature.

This article looks primarily at the first of these on particle concentration especially dust, and working in the dusty environment.

The Consequences Of Forming Dust Clouds

Dusts cause serious and violent explosions. One of the most notable cases concerns the use of corn starch powder at the Birds Custard factory in Banbury. In one instance, a starch powder cloud blew the site up in 1981 when it caught alight and  immediately combusted. It isn’t just small sites that are affected. Flour dust is also produced extensively in smaller businesses such as bakeries where it is spread on baking surfaces. It too is an explosion risk.

Ingredients used in food and pharmaceutical manufacturing are used as fine dusts to help with their functional performance as coatings or to speed up dissolution. It doesn’t always get managed easily. 

Chocolate is a good example where cocoa nibs are produced as fragments of crushed cocoa beans so that chocolate can be manufactured conveniently. In August 2020 the Swiss town of Olten was rained upon by fine cocoa powder when the ventilation system at the Lindt & Spruengli factory failed. Chocolate dust which had been managed within the factory environment was not constrained by the air handling system and dispersed over the town as a chocolate snow.

From a health point of view, it was found that nearly 400,000 premature deaths occur every year in Europe alone, from particulate pollution. Only recently in the UK, there have been high profile cases concerning exhaust particulates causing uncontrollable asthma. The same situation occurs in the USA too.

Another element of poor dust control is the cross-contamination of foods with allergens. Notable allergens discovered in dusts that have contaminated foodstuffs include egg powder, wheat powder, celery dust, dairy powders, cocoa with milk etc.

What is Particulate Matter (PM)?

Airborne particles or particulate matter (PM) covers a range of air borne pollutants. They can be solids to liquids, dry solid fragments, metal fragments, liquid droplets etc. All particles are defined by their diameter for air quality regulatory purposes. Particulates with a diameter of 10 microns or less (PM10) can be inhaled into the lungs and are often responsible for illness. Most fine particulate matter are particles that are 2.5 microns or less (PM2.5). PM1 refers to extremely fine material of 1 micron or less.

Air filtration systems are employed in environments to allow air to be recirculated. They are commonly multi-functional. These systems are designed with filters to remove fine air particles so  that air can be recirculated within the room. They often have a range of membranes filters which remove coarse and fine particulates with a high filtration efficiency. They are also designated as PM10, PM2.5 and PM1 in the USA to cover the particulates they can extract from the air and these designations are discussed fully by the USA Environmental Protection Agency.

A HEPA filters should remove 99.97% of all particulates that are 0.3 microns and over. That means removal of PM10, PM2.5 and larger allergens including pollen.

Both PM10 and PM2,5 type particulates can be produced by chemical combustion and through reaction.

The Type Of Processes in the Food And Pharmaceutical Industry That Produce Dusts

Processes that can produce hazardous dust to become airborne and endanger workers health in the factory or lab:

• Crushing, mixing, blending and ​milling.
• ​Screening, sampling, compressing, granulating.
• ​Pelletising, dispensing, ​drying, coating.
• Batching, weighing and ​packaging.

Typical Dust Producing Materials

• Cocoa powder, sugar, all powders used in drink mixes, citric acid and sodium citrate, artificial sweeteners, starch, flavour bearing powders in the snack industry.
• Toothpastes use baking soda and calcium carbonates
• Enzymes used in food processing
• Excipients used in tablets

Importance of testing dust

Filter media selection is determined by the characteristics of the dust, so it is important to have samples of dust from the application and facility tested by a reputable dust lab. A good dust collection equipment supplier will have an in-house dust testing lab and will offer testing at no additional cost. Dust test results help end users make informed decisions on the right air-to-media ratio and the correct cartridge media for the intended application. This is an important step to help mitigate cross-contamination of free-from products from other food particles. 

Dust testing should include analysis of the particle size, shape and characteristics of the dust at the food processing facility. Tests can also examine the dust’s true specific gravity and identify if the dust is hydroscopic or moisture absorbent. Abrasion testing helps to determine potential wear of the filters, as well as the optimal design of dust-handling components like valves, inlets and ductwork. Explosiveness testing that determines whether a dust is combustible helps to determine if additional design elements are required.

What makes a combustible dust?

In general, combustible particulates having an effective diameter of 420 μm or smaller, as determined by passing through a U.S. No. 40 Standard Sieve, are generally considered to be combustible dusts. However, agglomerates of combustible materials that have lengths that are large compared to their diameter and will not usually pass through a 420 μm sieve, can still pose a deflagration hazard. Therefore, any particle that has a surface area to volume ratio greater than that of a 420 μm diameter sphere should also be considered a combustible dust.

 The vast majority of natural and synthetic organic materials, as well as some metals, can form combustible dust. The NFPA’s Industrial Fire Hazards Handbook states:-

“any industrial process that reduces a combustible material and some normally non-combustible materials to a finely divided state presents a potential for a serious fire or explosion.”  

Evaluating the combustibility of a food or pharmaceutical dust

The type of combustible dust handled at your facility or production plant does not determine how explosive it actually is, only that it has the potential to combust. Finding out the risks posed by your particular dust requires a professional lab test, where a sample of your dust is ignited in a controlled setting, and then measured and analysed.

Two key elements of this analysis are the Kst value and the Pmax value of your dust. The Kst value measures the relative severity of an explosion, should your dust combust. The shape, size, and moisture level of the dust particles are only some of the factors that determine the dust’s Kst value. The Pmax value indicates the maximum pressure that would be created if your dust were to explode.

The dust explosion class reveals the severity of your dust exploding

Combustible types of dusts are divided into four classes: St 0, St 1, St 2, and St 3. A high Kst value will rank highly on the class scale, indicating a potentially violent explosion. Similarly, a Kst value of 0 means that there is zero risk of a combustible dust explosion.

• St 0: Kst value 0 – no explosion. Typical of silica dust, welding-generated dust and thermally generated dusts  such as cutting and some grinding processes.
• St 1: Kst value >0-200 – weak explosion. Typical of charcoal, powdered milk, sugar, sulphur, wood dust, zinc.
• St 2: Kst value >200-300 – strong explosion. Typical of cellulose, wood flour, polymethylacrylate (PMA).
• St 3: Kst value >300 – very strong explosion. Typical of metal dusts such as aluminium, magnesium and titanium.

Air Handling And Dust Regulations

In the USA there are a number of agencies that issue regulations relating to air quality. One of the pertinent ones for the food industry is in the Code of Federal Regulations (CFR). This is:-

• 21 CFR Part 110.20(b)(6)
  • Provide adequate ventilation or control equipment to minimize odors and vapors (including steam and noxious fumes) in areas where they may contaminate food; and locate and operate fans and other air-blowing equipment in a manner that minimizes the potential for contaminating food, food packaging materials and food contact surfaces.

The handling of combustible dusts legislation in the USA is through the National Fire Protection Association (NFPA), the Occupational Safety And Health Association (OSHA) and the EPA as referenced earlier.

In European/EU legislation, the main guidelines cover potentially explosive atmospheres (ATEX) where a mixture of air gases, vapours, mists, or dusts combine in a way that can ignite under certain operating conditions.

The legislation is now known as  Directive 2014/34/EU

According to the EU web-site this directive covers equipment and protective systems intended for use in potentially explosive atmospheres. It also defines the essential health and safety requirements, and conformity assessment procedures to be applied before products are placed on the EU market.

The legislation became applicable from the 20th April 2016 and replaced the previous  Directive 94/9/EC.

Other key pieces of EU legislation cover the  ATEX ‘workplace’ Directive 1999/92/EC which deals with the minimum requirements for improving the level of health and safety protection of workers potentially at risk from explosive atmospheres

In the United Kingdom as in Europe it is a requirement to conduct a COSHH assessment to establish the level of risk and hazard posed by dusts amongst other types of hazard.

As some pharmaceutical dusts are combustible, measures to prevent fire and explosion must be in place. DSEAR (Dangerous Substances and Explosive Atmospheres Regulations 2002) sets minimum requirements for the protection of workers from fire and explosion risks related to dangerous substances and potentially explosive atmospheres. The HSE gives guidelines for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids.

The COSHH definition of a substance hazardous to health includes; dust of any kind when present at a concentration in air equal to or greater than 10 mg/m3 8-hour TWA of inhalable dust or 4 mg/m3 8-hour TWA of respirable dust.

This means that any dust will be subject to COSHH if people are exposed above these levels, however, some dusts have been assigned specific WELs and any exposure to these must therefore comply with the appropriate limit.

Industrial Standards In The Air Filtration Industry: Classification Of Particulates

The standards used in air filtration have significantly changed in the last few years. Air handling is a key part of sanitation especially allergen management. In most cases, there is a rating known as the minimum efficiency reporting value (MERV) and this is used as a measure of filter efficiency.

The MERV scale was developed for the HVAC filter market and does not consider the way a dust collector pulse cleans filters periodically when a dust cake builds up. Measuring filter efficiency is discussed later in this article.  

MERV = 17 to 20, the minimum particle size is less than 0.3 microns. The type of controlled contaminants are carbon dust, viruses, sea salt and smoke. These filter system are found in electronic and pharmaceutical manufacturing clean rooms.

MERV = 13 to 16, this covers particles between 0.3 and 1.0 microns. Particles included droplet nuclei as in a sneezes, bacteria, cooking oil, most smoke and insecticide dusts, face powder and paint pigments. Filters handling these types of particles are found in hospitals and doctor’s surgeries

MERV = 9 to 12, covers particulates from 1 to 3 microns. This includes Legionella, humidifier dusts, nebuliser droplets, auto emission particulates etc. Generally systems for this type of air purification are found in hospital laboratories, good residential homes and general commercial facilities.

MERV = 5 to 8 have a minimum particle size of 3 to 10 microns. These will remove dust mite debris, cat and dog dander, hair sprays, dusting aids, custard and pudding mixes, mould spores.

MERV = 1 to 4 are all over 10 microns. This is pollen, dust mites, dander and material from insects, spray paint dust, carpet fibres. Most residential units will remove this type of dust.

Food dust particles are often small and difficult to capture and retain. Grain dusts can be as small as 5 microns, starches as small as 3 microns and milled flour down to 1 micron. Be sure that filtration efficiencies exceed 99.99 percent at 0.5-micron particle by weight and secondary HEPA filters are rated up to MERV 16.

How Do You Monitor Filter Efficiency?

Manufacturers of dust collector filters typically use two methods to express filter efficiency. Primary cartridge filters are measured by gravimetric analysis, which is based on particle capture by weight. For example, filter efficiency might be stated as 99.995 percent on particles of 0.5 microns or larger by weight. The efficiency of a secondary HEPA/iSMF, which is a static-loading filter may be expressed as a minimum efficiency reporting value, or MERV, based on a scale from 1 to 16, with MERV 16 being the highest efficiency.

Industrial Dust Collection

The approach to reducing dust particulates is managed through equipment called industrial dust collectors. An industrial dust collector gathers hazardous and nuisance dusts and fumes from the air before they settle on food and pharmaceutical manufacturing surfaces. Many facilities use dust collectors to keep process dust and fumes in check during manufacturing and processing operations to protect their workers and to comply with legislation.

There are several different types of dust collection systems that will satisfy a wide remit of requirements based on the facility’s size, type of process dust and application. There is no one particularly exceptional type of dust collector; some perform better than others for specific applications

The rest of this article considers the application of various dust filters from Camfil and Donaldson Corporation.

Some typical types of dust collection systems found in facilities include:

• Cartridge dust collector
• Baghouse
• Wet scrubber
• Portable dust collector 

Baghouses

Baghouses are also known as bag filters or fabric filters. The baghouse system removes dust particles from the air using a fan that forces the air through either a long cylinder-shaped bag or a box-shape made from woven fabric and in some cases glass fibre. These systems are capable of handling high volumes of dust-laden air. They use a pulse-cleaning system similar to a cartridge dust collector to reverse-blast dust through deformation of the filter bags.

Operation

Dust-laden air enters through the bottom of the dust collector then is filtered through the bags. The dust accumulates on the outside surface of the bags. At regular intervals, a burst of compressed air is shot through a parabolic nozzle that creates a shockwave, causing the particles to fall into the hopper. The filtered air is either recirculated or expelled outside, depending on the application and regulatory requirements.

Typical Applications

Baghouses work best for applications involving:

 

• High CFM (airflow)
• Harsh environments like mining
• Applications that produce high volumes of dust
• High-temperature applications
• Sticky or abrasive materials
• Dust contaminated with oil and moisture

The Cartridge-Style Dust Collector

Cartridge-style dust collectors are popular factory air cleaning systems that are multi-purpose. These  They work effectively in many different dust removal applications and operate in a similar way to bag collectors. These systems were invented by the Donaldson Company. 

Dust collectors use filter cartridges full of pleated nonwoven fabric called media to capture dust and fumes from the airstream as it moves through. The filter media provides a large surface area on which to capture dust.

The filter media is made from blends of polyester or other synthetic fibres and cotton or cellulose. These are often coated with nanofibers in order to release the dust better when the cartridges are pulse cleaned. Media can also be made of spun-bond fabric for increased durability against fibrous dusts and those that need high-efficiency filtration.

Camfil produce a DPS-Dura-Pleat filter media which is heavy-duty and based on an all-purpose polyester media. Other types of media include aluminized finishes for static dissipation. A media for hydro-oleophobic coated with an oil and water repellent finish. The other is a laminated polytetrafluoroethylene (PTFE) membrane for very high efficiencies of fine particulate and superior dust cake release.  

Operation

Cartridge-style collectors constantly suck in large volumes of air in order to filter out impurities that become airborne from production processes. The dust-laden air enters the collector through a baffled inlet and is forced through the filters where the dust becomes trapped in the filter media. The clean air continues through and out of the collector, where it is either vented out of the facility or recirculated back inside.

As the dust builds on the filter media over time, it begins to block the airstream, creating resistance. The resistance increases, causing the differential pressure within the system to rise. High differential pressure referred to as “pressure drop” causes the dust collector to work much harder to maintain the required airflow.

To relieve this pressure, the system pulses air through to clean the filters. This requires sending a blast of compressed air through the centre of the filter, which ejects the dust so it falls down into the hopper. Depending on the shape of the filter and the configuration of the media, some filters release more dust than others. To withstand rigours of pulse-cleaning, a number of filters need extra strengthening and support to ensure the filter life is longer, but it does mean lower operating costs.

Cartridge filters can save up to 40% space in comparison with conventional multi-pocket and tubular bag filters.

Notable suppliers of cartridge filters include Camfil with their Gold Cone™, Gold Cone™ X-Flo, Hemi Pleat® and Hemi Pleat® Extreme Media.

The latter allows for the base material to have larger pore sizes which means less of a pressure drop.

Applications for Cartridge Dust Collectors

Cartridge dust collectors are ideal for these applications:

• Food manufacturing and processing
• Solid dose pharmaceutical product manufacturing
• Welding, laser or plasma cutting
• Grain, seed and feed processing
• Woodworking
• Chemical processing
• Paper and metal packaging materials manufacturing

Wet Scrubbers

Wet scrubbers, also known as air scrubbers, use water or another liquid to remove dust particles from the air. Wet scrubbers are a popular choice for potentially explosive or flammable materials or operations where the slurry made up of liquid and collected dust particles can be reused.

Operation

A compact multi-application-use wet scrubber is used for sticky dusts.  It passes air and dust through a rough filtration system then skims it over the surface of the water called the scrubbing liquid. Some of the liquid flows through the vortex zone within the unit, which creates turbulence and atomizes the liquid into fine droplets. These droplets mix with the particle-laden air stream and are then removed by centrifugal force.

For more demanding applications with higher dust loading, a venturi system is a more effective choice. It injects water, via a pump, into the inlet of the unit. Extremely high velocities are generated which create contact surfaces with the scrubbing liquid. The result is an effective mixing of the scrubbing liquid and the contaminated air stream. The particle-laden droplets are separated from the airstream by centrifugal force.

Maintaining a clean or recycled water supply is important with wet scrubbers. The concentration of dust particles in the scrubbing fluid must be kept below 5% in order to maintain operating efficiency. If the dust is combustible, the amount allowed to accumulate in the discharge vats is regulated by NFPA.

Typical Applications

• Wet scrubbers work best for applications involving:
• Wet or sticky dusts
• Humid air
• Combustible dust

Portable Dust Collectors

Portable dust collectors, also known as unit dust collectors, are small and ideal for isolated jobs that produce dust. These jobs may or may not be located near a larger dust collection system. They can be strategically placed to capture dust from the source and can be used on their own or in tandem with a larger dust collection system to help extract any fugitive dust from the air.

Operation

Portable dust collectors work similarly to larger cartridge dust collectors but on a smaller scale. The unit contains a long collection arm and hood that can be positioned to collect dust and fumes at the source. Dust-laden air travels through the arm and passes through a cartridge filter. When the filter becomes overloaded, a shot of compressed air can be directed through the filter and dust releases down into the tray to be removed. It is important to note that portable dust collectors are not suitable for explosive dusts and solvent fumes.

Typical Applications

• Portable dust collectors work best for applications including:
• Isolated jobs not located near an inlet for your larger dust collection system
• Small shops that do not need a larger dust collection system
• Heavy dust load applications usually work in tandem with a larger dust collection system.

Where do you place a dust collector?

Effective dust collection relies on optimising its placement in the work area of a room to collect ambient airborne dusts and particulates. In most cases, placement and siting can be the weakest element in design because dust can settle before it ever reaches a collector, it might mean a short filter life and inadequate ventilation. It also means from an allergens point of view that cross-contamination of food for example is inevitable.

One of the most effective systems has dust collection as close to the source as physically possible. Stainless steel hoods are often sited above a work or production station. These hoods are located directly onto batch mixers and to high-velocity slots behind weigh stations.

An important design feature is being able to manage the dust once it is collected which is why placing dust collectors in specific and separate locations helps to remove the dust safely and without inducing further contamination.  It can then be cleaned further and the dust removed too.

Cartridge filters have long been used in the food and consumer healthcare industry.  Should  horizontally mounted filter cartridges be preferred to vertical mounted types? Horizontal mounting is high dust loading situation often means that dust does not get cleaned off the filter top. It is estimated that about a third of the filter is blocked or blinded by dust during operation. To get round this issue means rotating the horizontal filter from time to time to dislodge the dust but can also mean contaminants escaping into the air when the dust collector is opened. 

Another issue that regularly surfaces is the way in which incoming dust alights onto the top of a filter system. In these instances the heavy and abrasive particulates are also trapped because there is no pre-separation. This will pose a fire hazard  as sparks can enter the collector and form direct contact points with the filter cartridges. Abrasive particles will of course shorten  filter life.

Vertical mounted cartridges are claimed to allow dust to release uniformly from the filter pleats because there is no gravity aspect .to deal with. On that basis, filter life times are lengthened and the amount of time spent releasing particulates is reduced. In fact the filter compartment only needs to be opened when the filters need replacing.

Some operators prefer bag-in/bag-out systems to minimise exposure and reduce the potential for cross-contamination during a filter replacement.

The most preferred option for a vertical filter design is a wide-pleated cartridge that combines with a crossflow inlet. This is said to offer exceptional performance in capturing contaminant especially allergens by establishing a low pressure drop and a more consistent air flow. The air is better dispersed too during reverse pulsing and that means more efficient energy use. The direction of the pulse is straight down through the entire length of the filter and in combination with gravity forces the lighter dust particles into the hopper and out of the air stream.