Operating Costs – Installed, Rigid, and Flexible Containment in the Laboratory
Workspace for materials handling is at a premium in laboratories. Enclosed hoods occupy large amounts of wall space. Their advantage is vented storage space below the work surface for solvent storage. The potential for misuse is high. Most common is clutter from their use as storage spaces. Adherence to good work practices is often violated due to operational need, but also neglect. Both result in reduced air purge performance regardless of hood testing and airflow optimization.
Hoods dominate over the Heating, Ventilation, and Air Conditioning (HVAC) performance in laboratories. Room airflow balance is compromised whenever hood performance changes since hoods are often the primary room exhaust method. This places high demand on integrated room and hood airflow automation. A major operating cost is the continuous demand for conditioned room air and the cost of continuously operating blowers along with the associated air filtration, both of which must be scheduled for maintenance and certification with regularity.
Often forgotten is the original concept of ventilated bench-hoods – namely to contain potentially hazardous materials during handling while maintaining solvent concentrations at safe levels, i.e. below the lower explosive limit (LEL).
In practice, solvent handling areas should maintain solvent concentrations below the LEL, the most sensitive being hydrogen with an LEL of 0.4% hydrogen in room air. This applies to laboratories, manufacturing processes, maintenance operations, waste handling, and other potential solvent sources where a target concentration of <0.4% of any solvent or solvent mixture is prudent practice.
Hoods have been optimized through modification to access openings and baffle operations. Testing has shown that maintaining Occupational Exposure Levels (OEL's) of <1µg/cu. m at the workers breathing zone is a hit or miss affair. Standard practice is for laboratory personnel to use either partial or full personal protective equipment (PPE) when handling highly potent materials. Even then, testing has shown that finely milled materials, e.g. <3µm diameter lactose monohydrate, do not behave like gaseous emissions. Images of particulates suspended inside a hood show recirculation with deposition onto the inner glass surfaces immediately in front of the technician. This explains how room contamination is frequently detected. When technicians move away from the hood, their gloves, sleeves, and midriff carry the accumulated powder which is shed outside the hood during removal and disposal of the PPE. This contaminant spread is true of all type of open front airflow controlled hoods, even biological safety cabinets.
Walk-in hood performance is more compromised. It has proven possible to economically convert them to high potency materials handling spaces. The walk-in hood enclosure is used to house a fully contained flexible enclosure venting into the hood exhaust, yet with sufficient access to perform all necessary tasks. Because of cost and time to remove and assemble a replacement it is possible to modify an existing flexible enclosure needing additional access sleeves. An example of such an installation can be found on our web site at fabohio.com. Using this approach, such unmodified spaces have been turned into a valuable asset without incurring engineering modification or other time consuming modifications. Flexible containment removal and replacement for a large installation may take a full workday, but this is considerably faster than it would take to perform a cleaning operation after a spill in an open hood. Spill clean up would require the use of PPE with access limited to trained personnel. Uncontained spills are costly. Remediation is time consuming and places considerable strain on adjacent space access control and waste handling.
Both rigid glove boxes and flexible glove bags with integrated material pass-throughs and glovesleeves eliminate the need for controlled hood airflow and associated automation. Both provide full protection from powder materials as well as vapors. Flammable materials can be contained in glove bags by operating in an oxygen-limited environment (typically <4% oxygen) with venting through a combined particulate and solvent diffusional barrier. Alternatively a high flow air purge can be used with exhaust air-handling.
Conventional wisdom requires that rigid enclosures maintain a negative pressure inside the enclosure to overcome leakage due to breaches. The airflow is controlled using automation to maintain the control pressure. Flexible glove bags are less demanding of airflow than conventional rigid glove boxes. Maintaining a slight negative pressure inside a flexible enclosure is redundant for normal usage. The inherent flexibility balances any air pressure differential making air leakage (into or out of the glove bag) less likely in the event of a breach. In this mode of operation, the filter acts as a passive diffuser allowing bidirectional airflow. This results in a more effective barrier to particulates than when used as a conventional HEPA filter by preventing passage of particles <0.2 µm diameter.
Rigid glove boxes are designed for continuous venting through HEPA filters and must be exhausted using a snorkel attached to the room or adjacent hood exhaust to the scavenging system. Make-up air is required to satisfy the air deficiency. Combined HEPA/solvent filters are not normally used to permit room venting because they create a high pressure drop placing stress on the venting system.
One advantage of a rigid glove box is limited containment capability for an explosion. When an excursion exceeds the pressure relief capability, the net result is usually catastrophic failure of the protective viewing glass mounting.
Glove bag protection is afforded by the expansive ability of the material of construction, polyurethane formulations being the most forgiving. All of our flexible containment solutions will expand instantly without rupture as long as mounting restraints permit – one advantage of using elastic cords as tiedowns to a support frame. Polyurethane formulations used for flexible containment enclosures comply with automobile safety standards, being non-flammable.
Multiple use with immediate access is the forte of installed hoods. This is acceptable as long as a formal training program is provided for use and decontamination of protective equipment, e.g. bunny suits, coveralls, booties, respirators, etc.
Rigid containment can be a concern when changing products if clean down is required. Care is taken to finish the inside surfaces to a sanitary finish. Based on detailed cleaning studies this is also the most difficult to decontaminate. One vendor does deliver a more cleanable inner surface by nitric acid etching to remove the wire edges of the steel finish. Even with this finish, the minimum effective cleaning cycle including drying takes several hours and generates volumes of contaminated liquid waste, which must be collected and delivered to waste handling for disposal.
Rigid glove box cleaning tests using riboflavin are often accepted. Use of acid yellow milled with another powder, e.g. a milled 10:1 mixture of lactose monohydrate with acid yellow, tells a different tale. The visual acuity using fluorescent light is in the low percentile concentrations for riboflavin and parts per billion for acid yellow (40 ppb).
Flexible containment benefits from disposability. It is easily disposed of as a solid waste of low volume once the contained air is vented through the built in particulate/solvent diffusional barrier to collapse it. If free standing liquid resides inside the enclosure it is absorbed using cat litter to reduce the free liquid to acceptable solid waste conditions, e.g. <1% free liquid. Safe disposal of an entire operation can be accomplished with ease if optimum use is made of plastic goods for materials handling. It is a simple matter to bag-out reusable materials leaving plastic utensils inside to be contained within the collapsed enclosure destined for incineration. Waste is placed in suitable drums for shipment. Standard waste drums can contain several bench scale flexible enclosures.
An advantage both hoods and rigid glove boxes have over flexible enclosures – their resistance to pools of solvents requiring extended liquid contact.
Materials of construction for flexible containments are available to adapt to known solvents, e.g. polyvinyl alcohol is impermeable to methylene chloride but its use is limited since it is also soluble in hot water. Most polymer films have adequate resistance to solvent liquids and vapors for routine daily use. Compared with cleaning costs and lost time, the cost of replaceable flexible containment is competitive without either the capital investment or disposal challenges sustained by damaged or contaminated hoods or rigid glove boxes. The speed with which a flexible enclosure can be purchased, installed, used, and discarded favors their use even under unfavorable long-term contact conditions.
Installed and rigid structure costs are high and normally subject to the gamut of Design, Installation, Operational, and Performance Qualification (DQ, IQ, OQ, and PQ), frequently requiring continuing performance checks (PQ) once commissioned. Flexible containment is not subject to such demands being low cost disposable systems. Their use is supported by containment performance data generated by third party users. Their primary requirement is for use by trained, informed personnel. Flexible containment performance against cross-contamination is also matched by high containment capability.
Use as Storage
Secure storage is a valuable laboratory asset. Storage in hoods affects hood performance as mentioned earlier. It is also unsecured.
Glove box containment storage limits glove box functionality.
Flexible containment storage is economical in both space and cost. Once stored items are in place, the flexible containment can be partially collapsed to minimize space requirements by gently drawing air through the diffusional barrier. Once collapsed the enclosure and contents may be moved to their designated storage space. Any breach of the enclosure will be evident. This is especially useful when stored in a shared facility where cross-contamination control is of primary concern.
Performing further tasks inside a collapsed enclosure is a simple matter of attaching it to its support frame and allowing it to expand as air passes into the enclosure through the diffusional barrier. This procedure is passive since the flexible skin adapts to equalize the pressure differential.
Flexible containment enclosures are very adaptable. They can be designed for use in places where neither ventilated hoods or rigid enclosures could be installed and used, e.g. limited headspace, floor level, suspended, ergonomic challenges, etc. Any shape or size can be accommodated.
Rigid containment lighting is both an expensive and limited proposition. Flexible containment lighting is adequate using available room lighting. The film can be opaque or light blocking when diffuse lighting is required.
FabOhio, Inc. can provide all of the following methods for supporting flexible barriers as shown in the
customer examples on our web site:
- Inflatable bladders integrated into the enclosure. This method lends itself to installations having limited access such as inside a hood, or needing mobility such as mounted on a cart. No rigid support frame is needed.
- Supports made from hot water plumbing grade PVC piping and fittings. This method makes for rapid on-site assembly and adjustment such as for temporary structures or prototype development. When final dimensions are established the same structure can be made from more cosmetically appealing furniture grade PVC. Both are readily disposable and low cost. Plumbing PVC would cost ~$40 for parts and a cutting tool for a 4ft square enclosure. Construction time is <1 hour. A three airlock walk-in enclosure support would cost ~$80 for parts and 3 hours for assembly.
- Laboratory clamp and strut assemblies are frequently used for temporary use.
- Extruded aluminum support frames are custom made to measure and delivered to the site for assembly on location. Regular use of large disposable enclosures justifies the reasonable cost. The frames can be delivered within the same timeframe as the fabricated enclosure.
- Electro-polished stainless steel frames are often requested for quality reasons. They are the most cleanable, most expensive, and least capable of modification.
Examples of the above can be found on out web site.
Flexible containment has the added advantage that it can be operated at both increased and reduced pressure, e.g. ±20” w.g. This type of operation requires a rigid support frame and velcro style attachment heat sealed onto the enclosure seams.
After use, a flexible containment can be collapsed accordion style and stored in a small space until needed. The support frame can be made to collapse or the enclosure detached from the frame and stored. Such contained packages can be transported for storage elsewhere, including refrigeration. Use is enhanced by using a non-shedding sorbent pad to line the bottom of the flexible enclosure, either inside or outside the containment, For quality purposes and ease of replace the pad is placed beneath the enclosure. The choice of inside or outside is also determined by prevention of penetration by broken glass or wicking of liquid releases.
Why Consider Flexible Containment?
- Speed with which it can be designed, fabricated, and delivered (6 weeks or less from design to delivery).
- Low cost.
- Does not interfere with laboratory access during installation.
- Ease of custom design for specific requirements at off-the-shelf prices. Rarely is a flexible containment an off-the-shelf device.
- FabOhio, Inc. has an extensive database of designs which can be modified with ease. This is the most cost effective approach.
- Most flexible containments are ordered using credit cards eliminating the need for using formal purchase orders, unless needed for chain-of-custody purposes.
- Complex room size enclosures, e.g. including gowning/degowning, decontamination, and specialized airflow systems may require formal purchase order approval when a support frame is included.
- Even complex structures can be delivered in <6 weeks.
- Designs are often modified after first use, but low cost makes this feasible – unlike installed or rigid containment.
- Several design iterations can be achieved economically within weeks.
- Enclosures from modified existing designs can be scheduled for delivery within 3-4 weeks of placing an order.
- Flexible containment prototype mock-ups of conceptual rigid containments can be delivered economically for early user test experience. A succession of modified prototypes can be tested expediently at low cost. This enables a final rigid design to be presented with high confidence in the final product.
Overall, flexible containment in many forms has found a home in laboratories. Enclosure size and shape are virtually unlimited while the speed and cost with which it can become functional is unmatched.
Examples of customer installations can be viewed on our web site at fabohio.com.
FabOhio Inc. has over 50 years creating flexible containment, of which the last 20 years has been intimately involved with the growing needs of the pharmaceutical industry. We have encountered and engineered solutions to many challenges. We have few peers within the industry and competitors find it hard to challenge either our low prices or our customer support.
We would be pleased to discuss your needs.