Versatile, On-demand Isolation or Containment
Glove boxes are completely closed compartments ranging in size from a few cubic feet to several hundred cubic feet. Glove boxes differ from other safety enclosures in two significant respects: users can introduce articles into glove boxes and manipulate them inside through ports fitted with gloves, and glove boxes typically use a specialized atmosphere.
Glove boxes consist of the main chamber, two glove ports, and an air-locked antechamber for introducing labware and materials into the box. Opening the antechamber without taking preventive measures will introduce ambient atmosphere into the working chamber. This is dealt with by providing vacuum-assisted purging with the desired atmosphere. Sensitive applications will often add sensors for oxygen and/or water, with some type of scavenger mechanism to achieve ppm concentrations of those species. In regulated industries, the purge cycle is software-controlled and documented to ensure that materials are handled to specification.
“Glove boxes go under many different names and are used for many purposes,” says Mike Buckwalter, publications director at Terra Universal (Fullerton, CA). “Their essential attribute is the ability to maintain a completely separate environment from ambient.”
Although glove boxes are most often associated with biology, all scientific and engineering disciplines use glove boxes for one application or another. For example:
- Semiconductor/electronics – maintaining cleanliness for microchips or fabricated parts, sensor calibration
- Chemicals – manipulating dangerous, toxic, or moisture-sensitive substances
- Foods – air- or moisture-sensitive analyses
- Biology – cell culture, virus production
- Pharmaceuticals – compounding pharmacy, vaccines
- Controlled-atmosphere welding
Glove boxes are most commonly used when a process or operation requires low humidity or low oxygen levels, or when either the product/process must be protected from the lab environment or the operator needs protection from the process or operation. One often hears the terms “isolation” and “containment” with respect to glove boxes. Isolation is meant to protect the product, while containment refers to protecting the operator and/or environment. Isolation normally involves positive pressure, while containment operates under negative pressure.
“Containment and isolation are the major differentiators,” says Bob Applequist, product manager at Labconco (Kansas City, MO).
Materials of construction
Materials of construction are a significant glove box feature. Acrylics are transparent and low-cost, but life science applications that demand sterility require boxes made of sturdier materials that hold up better to cleaning and constant use. Stainless steel is most easily treated with a variety of cleaners and is the most durable material of construction, but also the most expensive. Most pharmaceutical glove boxes are made of stainless steel with sanitary fittings, as is required by Good Manufacturing Practices.
When static control is an issue, for example, when manipulating powders or combustible materials, acrylics are definitely out. Here, purchasers often specify stainless steel, which dissipates charges to ground, or electrically dissipative polyvinyl chloride.
Glove boxes may be positively or negatively pressurized, up to about 6 inches of water (17 inches equal one atmosphere). Pressurization puts strain on seals and limits the materials of construction, as large plastic or glass windows cannot withstand high pressures.
Top vendors will manufacture custom boxes, but most needs are served by off-the-shelf designs, with or without add-ons. For example, Terra Universal has several standard plastic and stainless steel designs, according to Buckwalter. “We try to avoid customization as much as possible by integrating standard modules with additional functionality, for example, gas filtration, controllers, sensors, automated doors, heating and cooling capability, and humidity control.”
Price, value, performance
A quick online shopping search for “glove box” leads to a dizzying array of devices ranging in price from $411 to $50,000, from simple plastic boxes to sophisticated mini–clean rooms that meet ISO sterility requirements. Glove boxes for regulated industries will almost always include pressure gauges, validatable oxygen and moisture monitoring, and built-in data transmission.
According to Applequist, price is the principal factor affecting most glove box purchase decisions. “Most of our customers have to watch their budgets.”
Any glove box can achieve very low oxygen or moisture readings, he explains, “but the cleaner it is on the inside relative to the outside, the greater the equilibrium difference.” Without taking additional measures, he says, “oxygen and moisture can creep up to 10 percent in 10 minutes.”
Customers, he says, often over specify for oxygen and moisture removal based not on actual data but on perception or assumption. “They know they want low oxygen and moisture, but when you ask them how low, 95 percent don’t really know. Maintaining 1 ppm levels 24 hours a day will be quite expensive, particularly with respect to scavenger systems.”
For more information and resources on glove boxes, please visit www.labmanager.com/glove-boxes