Hot Melt Adhesives and Available Types Used in Industrial Manufacturing
Industrial hot melt adhesives are polymer-based thermoplastic resins that, when melted, are used to bond materials together. Hot melt adhesives are comprised of one or more base polymers combined with tackifiers (which provide stickiness to the adhesive), plasticizers (to provide greater flexibility), and antioxidants (for protection against degradation) to allow for stability, adhesion, and flexibility.
Industrial hot melt is available in a variety of forms, including granular or powder hot melt blocks, pellets, bags, cakes, drums, and pillows. These materials are solid at room temperature, and then heated, melted, and dispensed for a variety of industrial applications.  As the adhesive returns to room temperature, a strong bond is created, adhering the manufacturing components together.
Hot melt can be dispensed as a liquid or, by introducing an inert gas (such as nitrogen) to the hot melt, as a foam.
Industrial Hot Melt Applications
In either liquid or foam form, hot melt adhesive is used across a wide variety of industries including  aerospace; automotive; product assembly; furniture making, cabinetry, and upholstery; product packaging; book binding; and non-woven sanitary hygiene products.
Aerospace and automobile manufacturers utilize hot melt adhesives for potting electronics (a process used to protect sensitive components from impact or vibration), as well as sealing rivets, seams, and joints. Additionally, hot melt foam is used in airplanes and cars as insulation around doors and windows to reduce vibrations and noise, as well as in seat assembly.
The pages in books and magazines are kept securely bound together using HMAs. The packaging industry depends on a strong adhesive bond to keep the flaps of corrugated boxes and cartons securely closed.
Non-woven personal hygiene products are manufactured by utilizing hot melt adhesives throughout the manufacturing process, including adhering the elastic strands in the leg openings and waistbands, bonding the fabric layers together to secure and stabilize the wetness core, and affixing the fastening tapes to the waistband.
Charring
Charring is a key concern when working with hot melt adhesives, as char (degraded adhesives that have oxidized, hardened into a gel, and been blackened and burned) can negatively affect the adhesives, cause equipment failure, and lead to a shut-down in production.
Key causes of charring include overheating (typically as a result of either using a temperature that is too high for a particular hotmelt, excessive heating times, or incorrect melt tank size); oxidation (exposing the adhesives to too much oxygen), and contamination (from dirt, dust and other materials that fall into the hot melt and burn).
Once formed, the char can break off into pieces that may clog filters and stop up spray and bead nozzles. The pieces of char can work their way onto the materials to be bonded, leaving marks, streaks, and uneven surfaces. Eventually, bits of char may get into hoses and pumps, breaking seals and scoring and damaging hoses and pump walls.
Why Nitrogen is Used for Hot Melt Adhesive
To reduce potential damage from charring, hot melt operators may elect to blanket the adhesives with nitrogen (N2) in a process by which nitrogen, an oxygen depleting gas, is piped into the space between the hot melt adhesive and the top of the hopper or melt tank. The nitrogen blanket protects the adhesive by creating a barrier against falling debris, and it also removes oxygen and moisture which may cause the hotmelt to oxidize and form char .
Oxygen Monitors Improves Quality Control and Helps Protect Employees
To preserve the integrity of the hot melt while blanketing with nitrogen, employees must maintain proper oxygen levels within hoppers or melt tanks, as too much oxygen can cause oxidation. Proper oxygen monitoring equipment should be placed inside melt tanks to measure and control oxygen levels.  A nitrogen leak could lead to failure of the nitrogen blanket, which could compromise the integrity of the adhesives.
Moreover, wherever nitrogen is used, the possibility of nitrogen leaks poses potential risks to humans. Since nitrogen displaces oxygen, a leak could deprive the air of oxygen, thereby creating a possible health hazard for personnel. When there is not enough oxygen in the air, persons working in the area can become disoriented, lose consciousness, or even suffocate due to the lack of oxygen. Since nitrogen lacks color and odor, there is no way, absent appropriate monitoring, for employees to detect a leak.
Best practice calls for oxygen deficiency monitors to be installed anywhere there is a risk of gas leaks. As such, oxygen monitors should be placed wherever nitrogen is stored, and in all areas where nitrogen is used.
PureAire O2 Deficiency Monitors
PureAire Monitoring Systems’ line of Oxygen Deficiency Monitors and Water Resistant Sample Draw Oxygen Monitors continuously track levels of oxygen and will alert hotmelt personnel to nitrogen leaks before employees’ health is put at risk.  In the event of a nitrogen gas leak, and a decrease in oxygen to an unsafe level, the monitor will set off an alarm, complete with horns and flashing lights, alerting employees to evacuate the area.
PureAire’s Water Resistant Sample Draw Oxygen Monitor is a self-contained oxygen deficiency system that is suitable for remote sampling of oxygen levels in confined spaces, hot melt tanks, and other locations where remote oxygen monitoring is required. The built-in pump samples oxygen levels from up to 100 feet away.
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PureAire oxygen monitors measure oxygen 24/7, with no time-consuming maintenance or calibration required. Built with zirconium oxide sensor cells to ensure longevity, PureAire’s O2 monitors can last, trouble-free, for over 10 years under normal operating conditions.Each PureAire O2 monitor has an easy to read screen, which displays current oxygen levels, for at-a-glance readings by hot melt manufacturers, who derive peace of mind from the monitor’s presence and reliability.

Frozen foods first became commercially viable in the 1930s, thanks in large part to Clarence Birdseye. He is credited with inventing the double-belt freezer, the forerunner to modern quick-freeze technology, which includes the tunnel freezers used by most major food processors in North America.

Frozen foods offer many benefits to today’s busy consumers, including convenience; minimal processing, with few to no preservatives; a long spoilage-free product shelf life; and, especially when compared with canned foods, superior taste, since the ingredients are quick-frozen at their peak of freshness. Seasonal foods, such as fruits and vegetables, are, once they have been frozen, now available year-round. In the same way, people living in landlocked locations can enjoy fresh-frozen seafood, no matter the distance from the coast. And, through the near magic of quick-frozen partially baked bread products, we can consume bakery-quality goods at home, straight out of the ovens in our own kitchens.

Still, even as Mr. Birdseye’s invention made frozen foods available to mass consumers in the first place nearly a century ago, so, too, have more recent innovations in freezing technology, including new freezer types, such as tunnel freezers using cryogenic gases, greatly improved the quality and, therefore, the market acceptance, of frozen foods. These freezers very quickly “flash freeze” foods at extremely low temperatures, such that the foods maintain essentially all of their original freshness, flavor, and texture.

How Tunnel Freezers Work
Tunnel freezers work by rapidly freezing food using cryogenic gases, such as liquid nitrogen (LN2) or carbon dioxide (CO2). The fresh food items are placed on a conveyor belt, which carries them into the freezer, where an injection system (utilizing either liquid nitrogen or carbon dioxide), together with fans circulating the gas-chilled air, ensure that all food surfaces are quickly and evenly frozen.

Food products frozen in cryogenic tunnel freezers, including all manner of proteins, fruits, vegetables, and parbaked bread and dough items, are ultimately shipped to grocery chains and warehouse superstores; operators of quick service, fast casual, and fine dining restaurants; and school and hospital cafeterias, among other places, and they are enjoyed daily by millions of hungry people.

Monitoring Can Protect Food Processing Employees
While the use of liquid nitrogen and/or carbon dioxide is essential in that part of the quick-frozen food processing industry using tunnel freezer technology, it is not without risk. LN2 and CO2 are both oxygen-depleting gases, and oxygen deprivation could put employees in real danger if there are gas leaks from freezer supply lines or exhaust systems, or from on-site gas storage containers. In the event of a leak, plant personnel could become disoriented, lose consciousness, or even suffocate from breathing oxygen-deficient air. Since liquid nitrogen and carbon dioxide are both colorless and odorless, workers would, in the absence of appropriate monitoring, have no way of knowing that there has in fact been a gas leak.
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PureAire Water-Resistant Dual O2/CO2 Monitors 
PureAire Monitoring Systems’ water-resistant dual oxygen/carbon dioxide monitors offer thorough air monitoring, with no time-consuming maintenance or calibration required. A screen displays current oxygen and carbon dioxide levels for at-a-glance reading by employees, who derive peace of mind from the monitor’s presence and reliable performance.

In the event of a nitrogen or carbon dioxide leak, and a decrease in oxygen to an unsafe level, the monitor will set off an alarm, complete with horns and flashing lights, alerting personnel to evacuate the area.
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PureAire’s dual oxygen/carbon dioxide monitor is housed in an IP67 water resistant enclosure that will keep the electronics dry during wash-downs and will remain accurate at extremely low temperatures.That makes the monitor ideally suited for facilities using liquid nitrogen or carbon dioxide, such as frozen food processing plants with tunnel freezers. Built with zirconium oxide sensor cells and non-dispersive infrared sensor (NDIR)cells to ensure longevity, PureAire’s dual O2/CO2 monitors can last, trouble-free, for over 10 years under normal operating conditions.