Tag: sterile conditions

GMP and Shoe Inn Products

Good manufacturing practices (GMP) are the practices required in order to conform to the guidelines recommended by agencies that control the authorization and licensing of the manufacture and sale of food and beverages, medical devices, pharmaceutical products, and cosmetics. These guidelines provide minimum requirements that a manufacturer must meet to assure that their products are consistently high in quality, from batch to batch, for their intended use. The main purpose of GMP guidelines is always to prevent harm from occurring to the end user.[1]

GMP covers the entire operation – everything from the materials used to employee personal hygiene. All guidelines follow a few basic principles, one of which is particularly relevant to Shoe Inn products:

  • Manufacturing facilities must maintain a clean and hygienic manufacturing area.

glovesProcedures, like wearing personal protective equipment (PPE), help maintain the clean and hygienic manufacturing area and reduce the risk of contamination. Garments such as smocks, hair nets, beard covers, disposable gloves, and shoe covers are donned beforeAll-shoe-covers-on-shoes-500entering critical environments and manufacturing areas. Oftentimes sticky mats, also known as tacky mats or cleanroom mats, are used in parts of facilities to pull contaminants off the bottom of street shoes prior to entering the gowning area or other sensitive areas. A newer technology that is being employed is the use of a UVC light sanitizing system to kill germs and pathogens on the soles of footwear.

Shoes on sticky mats

When it comes to adhering to GMP protocols, Shoe Inn has a range of products that will definitely help with maintaining clean and hygienic manufacturing areas.

[1] https://en.wikipedia.org/wiki/Good_manufacturing_practice

HealthySole: What, Why and Where?

For any problem, there are usually multiple solutions and people looking to improve upon those solutions by building a better mousetrap. When it comes to dealing with harmful organisms like germs and pathogens, existing solutions such as shoe covers and chemical baths may be less than ideal. For example, chemical baths need to be cleaned/maintained and can result in safety hazards with liquids being tracked around the facility. Enter HealthySole, a better mousetrap indeed!

What is HealthySole?

HS-Plus-2THealthySole is the missing solution to a truly disinfected environment. It is a groundbreaking active UVC light sanitizer that reduces contamination and infectious organisms with virtually no workflow interruption, monetary cost to operate or additional staff. HealthySole is the first clinically proven UVC product to kill up to 99.9% of exposed germs and pathogens, which can cause contamination and infections such as hospital acquired infections (HAIs), in only eight (8) seconds. In addition, it is a green technology that disinfects without harmful chemicals.

Why use HealthySole?

img-straight-onThis revolutionary product is essential in the reduction of spreading all pathogens that travel on the soles of footwear and cause contamination and infections. By adding HealthySole to an existing infection control program (such as booties or dedicated shoes), the facility will decrease the overall microbial load starting with shoe and floor contamination. Further, it will add a significant active layer of defense that reduces the rate of airborne, horizontal and cross contamination and does not incur additional labor costs. Lowering the overall microbial burden in a healthcare facility can lead to a decrease in HAIs. Facilities that have positive performance standards by lowering HAIs will reduce the additional treatment cost that is otherwise passed to them, shorten length of stay for patients, and save lives.

HealthySole could also allow you to replace messy chemical baths, thereby eliminating safety issues involved with people slipping on the liquids that are tracked around the facility.

Where would you use HealthySole?

HealthySole was originally invented and designed for hospitals and other medical facilities. In addition to hospitals, industries that could use HealthySole include food processing, laboratory animal research, etc. Bottom line, you can use HealthySole almost anywhere you are concerned about controlling dangerous microorganisms.

Shoe Covers in Specific Industries: Food

Cleanliness is vital in the food manufacturing/processing industry (growers, processing plants, etc.) in order to prevent contamination and avoid negative food safeiStock_000013166962Smallty headlines. Along with thorough hygiene practices and sanitation, wearing personal protective equipment such as gloves, beard covers, hairnets, and shoe covers can make a significant difference in reducing food contamination. Here are a few reasons why Shoe Inn shoe covers are crucial in preventing food contamination and the overall food industry:

  • Decreasing Outside Contamination

Tracking outside contaminants into clean environments on the bottoms of shoes is a iStock_000019685054XSmallpotential health hazard in the food industry. New shoe covers are clean and will keep any outside contaminants contained inside the covers, thereby preventing them from being introduced into food products.

Just as it is important to not introduce outside contaminants into the sanitary environment where food is processed/handled, it’s equally important to ensure nothing from the shoe covers gets left behind. Fortunately, the clips on Shoe Inn shoe covers have been designed so that they remain in place during application, wear, and removal.

  • Increasing Safety

Spills happen in the food industry and can be a significant safety hazard in terms of slipsunlucky carefree business man silhouette and falls. Some shoe covers are liquid proof and include non-skid/anti-slip coatings, helping to decrease slipping incidents and thereby promote safety.

Bottom line, shoe covers are an important piece of an overall food safety program and can also improve workplace safety in the food industry.

Seven Reasons to Utilize Revolutionary Automatic Shoe Cover Dispensers and Removers

There are multiple methods for businesses and organizations to keep their facilities clean and minimize or prevent contamination from the wide variety of contaminants that exist on shoes.  The four most prevalent options are shoe covers/booties (disposable or reusable), dedicated/facility shoes, sticky/tacky mats, and chemical baths.  The relative pros and cons of these will be discussed in a future blog post.  This blog post focuses on shoe covers and a revolutionary technology for putting them on and taking them off.

Shoe covers are essential in many applications for keeping environments clean and free from contamination.  In some cases, you want to prevent whatever is on the floor from getting on your shoes.  Other times you want or need to prevent contaminants on your shoes from getting on the floors in your environment for maintenance and sanitation, health and safety, infection control and other reasons.  In the past people had to apply and remove their shoe covers manually, but this is time-consuming, can be dangerous, and is definitely not clean.  Alternatively, many entities are now utilizing automatic shoe cover dispensers and removers to address these issues.  Here are seven reasons why:

  • Speed: it’s faster

No bones about it, putting shoe covers on the old-fashioned way is time-consuming – the entire process, which includes grabbing a pair of shoe covers and finding a place to put them on, easily takes somewhere between 30 and 45 seconds each and every time.  Removing them can take even longer, especially in an environment that requires more extensive hygiene practices.  With Shoe Inn’s revolutionary automatic shoe cover dispensers and removers, the time is reduced to about five (5) seconds!

  • Efficiency = productivity = $$$

Applying shoe covers faster and more efficiently means employees can get to work faster. The Shoe Inn system makes the process of applying and removing shoe covers AT LEAST four times (4x) faster.  This significantly shorter gowning time equals increased efficiency that translates to increased productivity, meaning you are not wasting money paying your employees to put on shoe covers but instead are paying them in their work environment where they are being productive. Cumulatively, these small time saving increments add up to big savings for your business!

  • Easy breezy

Putting shoe covers on is easy for some people, a walk in the park.  However, for others it can be a real challenge for a variety of legitimate reasons. Many, many times we’ve been told by people at tradeshows (with colorful, choice words) how much they despise, detest, even flat out refuse to put shoe covers on.  Employ automatic shoe cover dispensers, which make it so much easier to put booties on, and those challenges and objections will vanish, thereby increasing compliance.  Same goes for the remover, just at the back end of the process.

  • Safety rules

Automatic shoe cover dispensers and removers keep employees and visitors safer by iStock_000020353612Largereducing the risk of injuring themselves while putting shoe covers on and taking them off.  Instead of bouncing around while attempting to balance on one foot and lifting the other leg, which we have dubbed the “bootie hop” (see The Bootie Hop video), people can safely apply and remove their shoe covers in an ergonomically friendly manner.  The handlebars found on the Shoe Inn Stay dispenser and both ASCR removers make it even safer and easier.  Say goodbye to those workers’ comp claims!

  • It’s cleaner

Open hand raised, Stop Bacteria sign painted, multi purpose concPutting shoe covers on and taking them off by hand is dirty business.  Your shoes, particularly the bottoms, are gross – just think about everything you’ve stepped in and on while walking around streets, parking lots, subways, parks, trails, public bathrooms, etc.  It is almost inevitable that you’re going to touch your shoes while putting shoe covers on manually and thus contaminate your hands.  Depending on the environment, used shoe covers can be soiled as well so automatic shoe cover removers do the dirty work for you.

  • Save precious space

Oftentimes wherever shoe covers need to be put on and/or taken off, space is at a Cleanroom employee putting on shoe covers and using a sticky matpremium.  Gowning benches and chairs take up space and can be obstructions.  Shoe cover dispensers and removers take up much less space, especially proportionately when factoring in how much more efficient they are in facilitating people getting through the process.  Fewer benches and chairs mean more space for other necessities.

  • Dressed to impress

Starward-virtual-proof-2Manually putting shoe covers on and taking them off is so old school.  While there will always be a place for doing certain things the old-fashioned way, why not look professional and impress your customers, visitors, regulators, inspectors and auditors?  In fact, you can customize your Shoe Inn dispensers and removers with your corporate logo, motto/slogan, contact information, etc. to further cement your brand.

As you can see, there are many benefits to implementing an automatic shoe cover dispensing and removal system.  Want to know more?  Check out our line of shoe cover dispensers, shoe covers and removers or contact us.  At Shoe Inn, we make putting shoe covers on and taking them off faster, easier, safer and cleaner!

Cleanrooms

Cleanroom scientists wearing shoe coversCleanrooms (or clean rooms) are used in virtually every industry where small particles can adversely affect the manufacturing process.  Typically located in scientific research or manufacturing settings, a cleanroom is a controlled environment that has a controlled level of contamination (pollutants such as dust, airborne microbes, chemical vapors, and aerosol particles) that is specified by the number of particles per cubic meter (m3) or per cubic foot (ft3) at a specified particle size.  Believe it or not, the ambient air outside in a typical city environment contains about 35,000,000 particles per m3, 0.5 μm and larger in diameter, which corresponds to an ISO 9 cleanroom.  At the other end of the spectrum, an ISO 1 cleanroom allows no particles in that size range and only 12 particles per m3 of 0.3 μm and smaller.

Cleanroom Overview

A cleanroom is any given contained space where provisions are made to reduce particulate contamination and control other environmental parameters such as pressure, temperature, and humidity. The key component is the HEPA (High Efficiency Particulate Air) filter that is used to trap 99.97% of particles that are 0.3 microns and larger in size. All of the air delivered to a cleanroom passes through HEPA filters, and in cases where more stringent cleanliness performance is necessary, ULPA (Ultra Low Particulate Air) filters are employed.

The use of multi-layer adhesive mats for cleanrooms is almost universal.  Matting can vary in size, color, placement, and number based on the characteristics and logistics of each individual cleanroom.

Personnel who work in cleanrooms go through extensive training in contamination control theory, practices and procedures. They enter and exit the cleanroom through air showers, airlocks, and/or gowning rooms, and they must wear special clothing designed to trap contaminants that are naturally generated by our bodies.

Depending on the room classification or function, personnel gowning may be as limited as lab coats and hairnets/beard covers, or as extensive as being fully enveloped in multiple layered bunny suits with self-contained breathing apparatus.  The cleanroom clothing itself must not release fibers or particles to prevent contamination of the environment.

Cleanroom garments include things such as boots, shoes, shoe covers, beard covers, hairnets, bouffant caps, facemasks, coveralls, aprons, frocks/lab coats, gowns, glove and finger cots, hoods, and sleeves. The type of cleanroom garments used reflects the cleanroom classification and product specifications. For example, Class 10,000/ISO 7 cleanrooms may use simple smocks, head covers, and shoe covers.  On the other hand, careful gown wearing procedures with a zipped coverall, boots, gloves and complete respirator enclosure are required for Class 10/ISO 4 cleanrooms.

Cleanroom technicians wearing shoe covers
Cleanroom technicians wearing shoe covers

Air Flow Principles for Cleanrooms

Cleanrooms maintain particulate-free air through the use of either HEPA or ULPA filters employing laminar or turbulent air flow principles. Laminar, or unidirectional, airflow systems direct filtered air downward in a constant stream. Laminar airflow systems are typically employed across 80% to 100% of the ceiling to maintain constant air processing and unidirectional flow. Laminar flow criteria are mandated in ISO 1 through ISO 4 cleanrooms.  Turbulent, or non-unidirectional, air flow uses both laminar air flow hoods and non-specific velocity filters to keep cleanroom air in constant motion, although not all in the same direction. The rough air seeks to trap particles that may be in the air and drive them towards the floor, where they enter filters and leave the controlled environment.

Proper cleanroom design encompasses the entire air distribution system, including provisions for adequate downstream air returns. In horizontal flow applications, this involves the use of air returns at the downstream boundary of the process.  In vertical flow rooms, it requires the use of low wall air returns around the perimeter of the zone.  It should be noted that the use of ceiling mounted air returns is contradictory to proper cleanroom system design.

Cleanroom Classifications

Cleanrooms are classified by how clean the air is according to the number and size of particles permitted per volume of air. Federal Standard 209E is used here in the U.S.  The newer standard is TC 209 from the ISO (International Standards Organization).  Both standards classify a cleanroom by the number of particles found in the laboratory’s air. The cleanroom classification standards 209E and ISO 14644-1 require specific particle count measurements and calculations to classify the cleanliness level of a cleanroom or clean area.

Large numbers like Class 1,000 or Class 100,000 refer to FS 209E, and denote the number of particles of size 0.5 µm or larger permitted per ft3 of air. The standard also allows interpolation, so it is possible to describe other classes such as Class 2,000.

Small numbers refer to ISO 14644-1 standards, which specify the decimal logarithm of the number of particles 0.1 µm or larger permitted per m3 of air.  For example, an ISO 4 cleanroom has at most 104 = 10,000 particles per m³.

Both FS 209E and ISO 14644-1 assume log-log relationships between particle size and particle concentration. For that reason, there is no such thing as zero particle concentration.

US FED STD 209E cleanroom standards

Class Maximum particles/ft3 ISO equivalent
≥0.1 µm ≥0.2 µm ≥0.3 µm ≥0.5 µm ≥5 µm
1 35 7.5 3 1 0.007 ISO 3
10 350 75 30 10 0.07 ISO 4
100 3,500 750 300 100 0.7 ISO 5
1,000 35,000 7,500 3,000 1,000 7 ISO 6
10,000 350,000 75,000 30,000 10,000 70 ISO 7
100,000 3.5 x 106 750,000 300,000 100,000 700 ISO 8

ISO 14644-1 cleanroom standards

Class Maximum particles/m3 STD 209E equivalent
≥0.1 µm ≥0.2 µm ≥0.3 µm ≥0.5 µm ≥1 µm ≥5 µm
ISO 1 10 2.37 1.02 0.35 0.083 0.0029
ISO 2 100 23.7 10.2 3.5 0.83 0.029
ISO 3 1,000 237 102 35 8.3 0.29 Class 1
ISO 4 10,000 2,370 1,020 352 83 2.9 Class 10
ISO 5 100,000 23,700 10,200 3,520 832 29 Class 100
ISO 6 1.0 x 106 237,000 102,000 35,200 8,320 293 Class 1,000
ISO 7 1.0 x 107 2.37 x 106 1,020,000 352,000 83,200 2,930 Class 10,000
ISO 8 1.0 x 108 2.37 x 107 1.02 x 107 3,520,000 832,000 29,300 Class 100,000
ISO 9 1.0 x 109 2.37 x 108 1.02 x 108 35,200,000 8,320,000 293,000 Room air

How to Transition from ‘Dirty’ to ‘Clean’ While Booting Up in a Gowning Room

Prior to entering a cleanroom, employees need to get “gowned up” in special clothing designed to trap contaminants that are naturally generated by our bodies.  Depending on the room classification or function, personnel gowning may be as limited as hairnets/beard covers and lab coats, or as extensive as being fully enveloped in multiple layered bunny suits with self-contained breathing apparatus.

The Gowning Room

cleanroom-gowning-area-600

Cleanroom personnel generally “boot up” in dedicated shoes or shoe covers, and in order to make sure they don’t get contaminants on the shoe covers before entering the cleanroom, they typically follow a transition protocol from the “dirty” to the “clean” side of the floor/room.  This usually entails a gowning bench or chair placed along a line that has been taped or painted on the floor, or along the line between two different colored floor tiles.  While sitting, the employee puts the first shoe cover on, puts that foot down on the “clean” side, then repeats the action for the second foot.  Sometimes regular shoe covers tear while being put on, so the employee has to take them off, throw them away, and start the process over again.

A much easier, safer, and faster way of putting shoe covers on is to use a Shoe Inn automatic shoe cover dispenser.  These dispensers are similarly placed along the line between the “dirty” and “clean” parts of the floor.  In this setup, while standing on the “dirty” side, the employee puts the first shoe cover on, puts that foot down on the “clean” side, then repeats the action with the second foot and proceeds to the next step in the gowning process.  Because the employee does not have to go grab precisely two shoe covers, walk to the bench, sit down, put the shoe covers on, and stand back up, not to mention not having to deal with improperly sized and torn shoe covers, the “booting up” process is much more efficient, which can help alleviate gowning room bottlenecks and significantly improve productivity.

Sticky Mat Protocol for Use in Cleanrooms

Shoes on sticky mats
Sticky mats help trap dirt!

While many companies use shoe covers to prevent contamination, many Shoe Inn customers also use sticky mats to maximize contamination prevention.  The utilization of multi-layer adhesive mats for cleanrooms is almost universal. However, how the mats are used is unique to each cleanroom. Mats can vary in size, color, number, and placement based on the logistics and characteristics of each individual cleanroom.

Placement

Mats should be placed in an area where they will be on clean, hard flooring. They should be placed just before or just after the ingress/egress point for each cleanliness or control change. It is suggested that the placement sites are worked backward from the final clean area or cleanroom.
Cleanroom employee putting on shoe covers and using a sticky mat

  • cleanroom – gowning area
  • cleanroom – staging area
  • gowning area – control area
  • control area – common hallway
  • common hallway – warehouse or receiving
  • common hallway – public area

Matting should be placed so that all those passing through that point must step on the mats. Matting should be placed with the longer dimension of the mat in the same direction as the traffic flow for maximum footfalls on each mat. The minimum number of footfalls should be two with each foot for each location.

Size

The proper size mat for each area of placement depends on the width of the opening and the variance and direction of the traffic. Normally the width of the mat should be 2/3rds to 3/4ths of the width of the doorway. It does not normally need to cover the full width because ordinary traffic passes through the middle of the doorway and not along the edge. However, if the traffic enters at a sharp angle or from the side of the entryway, then the width of the mat needs to be wider than the doorway to allow for enough footfalls.

As stated above, the length of the mat should be long enough to provide at least two footfalls with each foot at each location. Usually this is a minimum of 45 inches.

Color

The color of the mats, which has no effect on the function of the mat, can vary from standard blue, white, and grey to custom colors and printed messages. In general, white shows the most dirt and particulates, and is normally preferred to make sure the layers are changed at frequent enough intervals. However, grey and blue work just as well when a maintenance schedule is set.

Layer MaintenanceSticky mat with shoes and cart

How often the layers should be removed depends on a number of factors:

  • How dirty the area the personnel are coming from is.
  • The number of people or pairs of feet per shift or per hour.
  • The difference in cleanliness between the areas.
  • The size of the mats and how many mats or locations are in the series.

In general, areas farther away from the cleanroom will be dirtier. Changing the layers at this point of use every half hour would be a benchmark with which to start. The final entry area into the cleanroom is probably from a clean area to a very clean area and each layer may last 4 to 8 hours.

However, this is just a rough guideline and each point of use will vary greatly. A few days of use and observation will help to determine the optimal mat layer change interval.

Installation

  1. Before placing a new mat down or replacing an existing mat, thoroughly clean the surface to remove contamination that may act as a barrier and keep the mat from properly adhering to the floor. Make sure to remove any adhesive residue if you are replacing an existing mat. It is recommended to use a pre-saturated wiper that contains a percentage of isopropyl alcohol. Make sure the surface is completely dry before application.
  2. To apply the mat, remove half of the release liner in the long direction of the mat, which will help with the alignment of the mat.
  3. Once you have the mat properly aligned in the location you want, start smoothing out the half of the mat with the adhesive exposed. Start at one end and work toward the middle making sure you do not trap air under the mat as you go, then remove the rest of the release liner and smooth the rest of the mat out in the same direction in which you removed the release liner.

Storage

Matting should be stored flat and for several hours in similar climate conditions as the point of use. For ideal results, the mats should be used in a controlled environment setting but may be placed in any area that has a temperature of 54-95 oF (12-35 oC).

Long-term storage of mats should always be on a flat and hard surface. Storage on the original shipping pallet is recommended. Normal warehouse conditions are usually acceptable but extreme temperatures (less than 32 or greater than 105 oF / 0 or 40 oC) should be avoided.

Storage of mats longer than one year from the date of purchase is not recommended. However, under normal storage conditions, matting should not have any variation in performance for a period of up to three years.

Summary

The utilization of multi-layer sticky mats for cleanrooms is almost universal.  In fact, many customers who use the Shoe Inn automatic shoe cover dispensing system also use these adhesive mats to further help prevent contamination within controlled environments.  Depending on various factors such as how dirty the area the personnel are coming from is and the level of cleanliness desired or mandated, this combined approach may be advisable or even required.

Who Needs an Automatic Shoe Cover Dispenser?

An automatic shoe cover dispenser, who needs that?  When it comes to putting on shoesitting-bench-shoe-covers-158 covers, you don’t think much about it — you just do what you’ve always done, sitting on a bench or balancing on one leg while trying to put a shoe cover on the other foot (what we call the “bootie hop”).  Sounds simple, but for many people it is not.  If you find it difficult to bend over and tie your shoes or to balance on one leg, then you know how challenging it can be to put shoe covers on.  Quite frankly, most people who have to wear shoe covers despise putting them on.  Also consider workplace injuries happening during the process of putting them on — they do happen.  In fact, the “bootie hop” is a worker’s comp claim waiting to happen.  Last but not least, what about the bottleneck that is created when you have a lot of people who need to put them on at the same time?  Shoe Inn can help alleviate all of these issues.  Shoe Inn automatic shoe cover dispensers are ideal for use in a variety of environments such as manufacturing and food processing plants, laboratories and clean rooms, medical and healthcare facilities, and anywhere else people need to put shoe covers on faster, easier, safer and cleaner.  There is no doubt that you will benefit from the ease of use, time savings, and added safety from using Shoe Inn automatic shoe cover dispensers.

Importance of Using Shoe Covers

Petri dish with bacteriaHave you ever considered what is on the bottom of your shoes?  Besides things you can see, such as grease, oil, gum, mud, leaves, feces, etc., there are the countless things you cannot see, like germs, bacteria, mold, and viruses.  All of these things walk with us everywhere we go, from the house to the car to the parking lot to the building to the lab or production area to the bathroom to the dining area and back again.  How many other places do we go, like gas stations and public parks, picking up things on our shoes all along the way and transporting them where they are unwelcome?

As a result, many industries and settings require the use of shoe covers to maintain sanitary or sterile conditions, prevent contamination, limit the spread of infections, comply with health codes, etc.  A review of the literature turned up several key findings such as the following:

“In this study, the authors subjected six occupied rodent holding rooms in their animal research facility to three conditions: use of disinfectant mats; use of shoe covers; and no disinfectant mats or shoe covers. The authors took bacterial culture samples from the rooms under each condition. There was no significant difference in the mean number of colony forming units (CFUs) cultured when the disinfectant mats or shoe covers were used. However, the mean number of CFUs obtained was significantly lower when either disinfectant mats or shoe covers were used than when neither was used. These results suggest that using disinfectant mats or disposable shoe covers may reduce the bacterial load on rodent holding room floors.”[1]

“We recommend that gloves and footwear worn by employees who handle RF-RTE foods or who work in areas where RF-RTE are processed or exposed be made of impermeable material, in good repair, easily cleanable or disposable (emphasis added), and used only in RF-RTE areas.”[2]

“Health care workers who handle hazardous drugs are at risk of skin rashes, cancer and reproductive disorders. NIOSH recommends that employers provide appropriate personal protective equipment (PPE) to protect workers who handle hazardous drugs in the workplace…Use hair and shoe covers constructed of coated materials to reduce the possibility of particulate or microbial contamination in clean rooms and other sensitive areas.”[3]

Based on the above, it is clear that using disposable shoe covers is a credible and recommended method in a variety of situations and controlled environments.

[1] Allen KP, Csida T, Leming J, Murray K, Thulin J. Efficacy of Footwear Disinfection and Shoe Cover Use in an Animal Research Facility, U.S. National Library of Medicine, http://www.ncbi.nlm.nih.gov/pubmed/20305633

[2] US Food and Drug Administration, Guidance for Industry: Control of Listeria monocytogenes in Refrigerated or Frozen Ready-To-Eat Foods, Section XI, Paragraph IV

[3] Personal Protective Equipment for Health Care Workers Who Work with Hazardous Drugs, https://www.cdc.gov/niosh/docs/wp-solutions/2009-106/pdfs/2009-106.pdf