Putting up the barriers

Traditionally, airflow containment or dust capture hoods systems have been ideal for laboratory use, but as we become more and more H&S conscious, do we need to move to a different model? 

Many laboratories carry our powder weighing or powder processing on a small or micro scale. Traditionally, airflow containment or dust capture hoods systems have been perfectly adequate for these operations as the quantities of material being handled are very small.

Safety however, is reliant on a number of factors – the most critical of which being how hazardous the material you routinely handle is. Many materials are now provided with Occupational Exposure Data which prescribes the material or compound’s maximum daily exposure – often in terms of µg/m³ dust concentration over an 8 hour time weighted average. Here again, the short duration of most laboratory operations reduces massively the 8 hour TWA.

The problem is the exposure limit and potential to generate airborne dust in typical laboratory operations. For example, some pharmaceutical compounds have extremely low exposure limits that are in the range of nanogram/m³ exposure level. To put this into perspective – if you take a grain of table salt typically weighing 150µg – then this single crystal ground into dust is equivalent to a breathing concentration of 15µg/m³ over an 8 hour shift (assumes 10m³ inhalation/shift). So by comparison, some of the new high potency pharma materials with sub 50ng/m³ exposure limits equate to an equivalent of 0.00333 of a grain of salt – inhaled over 8 hours.

This, while not a very scientific method of exposure visualisation creates the realisation that when handling some highly active materials in the lab a higher level of protection may be required. In the containment industry, we tend to pigeonhole materials and operations into a risk and hazard analysis. For example, the hazard driven by the exposure limit of the powder being handles is traded off against the risk of exposure. Obviously weighing a milligram of (50ng/m³ OEL) powder in a good VBE should not generate any significant aerosol cloud or contamination risk. Scale things up to a few hundred grams and can you be sure that your lab coat is free of trace particles that could create an exposure risk?

There is a growing trend in pharmaceutical laboratories to move away from traditional airflow containment to “barrier Isolation”, where the operator handles the materials via a screen and glove ports – eliminating both respiratory and clothing contamination risks.

We spoke to leading containment consultant Paul Gurney-Read of Gurney-Read Consulting to clarify if there is a simple cut-off point between safe use of airflow containment and barrier isolation.

LN What is the easiest tool for a scientist to use to identify when the move to barrier isolation is needed?

The problem with trying to devise a tool has always been the variability in nature of the operations to be contained.

To determine the engineering control required to contain an activity we must review the hazard (product) against the exposure potential, i.e., scale, dustiness of powder and expected volume and velocity of dust generated.

It then requires some experience of the performance capabilities of airflow cabinets vs isolators to determine which is required. So unfortunately, there is no simple cut off point. I have however assisted some major pharma clients to develop a matrix that compares material OEL with Scale to determine when an airflow cabinet should provide the required containment. Others have done this for themselves using collated test data from existing equipment. Even then, the activities must still be assessed to ensure that dust is not being generated at high quantities or velocities. Observation of the technician performing the tasks is usually sufficient. Examples of rules:

- All materials with OEL<30ng/m3 must be handled in isolators. - For mass >100mg and OEL<500ng/m3 isolators are required.

The actual long term containment performance of airflow devices may be considerably less than reported by some suppliers. This is due to the suppliers data being taken from tests performed under tightly controlled conditions. In reality, there will be considerable variability in operator techniques and operator performance can fall over time as training becomes diluted.

LN Can working practices (SOP’s) extend the use of airflow containment to very low exposure limit compounds?

The success or failure of using open devices, relying on a face velocity to contain, is that the performance is very dependent on the dust generating nature of the activity, as we just discussed, and the performance of the operator. With most proprietary devices providing a face velocity between 0.3 and 0.5m/s, it is easy for the operator to move in a way that generates air currents greater than this and therefore potentially allowing material to escape. I have witnessed operations that failed the first containment tests, only to pass easily when the activity was adjusted or the operator properly trained. The other issue with open fronted devices is “tracking”, i.e. the escape of material from inside to outside the cabinet by deposition on gloves, sleeves or materials.

Good handling practice, such as not removing contaminated gloves and sleeves from the cabinet and thorough cleaning of materials prior to exiting the cabinet is necessary to avoid this. Bag-out ports, built into the units, should be more common place to assist with disposal of gloves, sleeves and waste. So, good work practices can extend the use of airflow cabinets, in fact they are essential, but while we rely on procedures and operator performance to ensure high containment levels there will always be a risk of failure.

LN Assuming either airflow containment or barrier isolation systems are in use in a laboratory – what methods are available to ensure safe performance?

In Europe, Directive 98/24/EC – risks related to chemical agents at work, states that “the employer must regularly measure chemical agents which may present a risk to workers' health, in relation to the occupational exposure limit values and must immediately take steps to remedy the situation if exceeded.” Therefore when you first purchase your containment device you should measure the airborne concentration. You can do this using a surrogate test. The results can be used both to confirm that the equipment has met any performance guarantees, sort from the equipment suppliers, and to set an operator protection strategy.

The surrogate test should mimic the actual operation as closely as possible and be performed by technicians using agreed upon procedures. Airborne samples are taken, by extracting air through a filter, in the operators breathing zone and at various points around the equipment to assist in identifying areas where containment may have been breached. A placebo or surrogate material is selected that has the necessary analytical sensitivity to give results at least an order of magnitude lower than the CPT. Three or more identical tests should be carried out to increase the confidence in the results. Test requirements should be identified in a protocol, i.e. containment performance target (CPT), procedure, surrogate material, gowning requirements, sample positions etc. This will help eliminate mistakes and the generation of false results.

The samples collected during the test can be analysed by the company’s own lab, if they have an approved method, or sent to an accredited laboratory. The mass collected on the filter can then be converted to an airborne concentration and this compared to the CPT. As the data set will be small, statistical analysis of the results is recommended as described in BS EN 689 or by using the IHSTAT method, as developed by the American Industrial Hygiene Association. If the equipment is to be used by an operator for less than 8 hours per day then the CPT can be modified proportionally.

The company may be in a position to use real product and operations to compile this data. Once in operation the company should risk assess any changes that may affect the containment performance of the equipment, i.e. should a more potent material be used or the activity within the equipment change. Containment performance should then be periodically confirmed (every 12 months) by performing Parametric tests, such as face velocity. Exhaust filter condition should be monitored to ensure the filters are not becoming blocked or are defective.

The authors:

Martyn Ryder is Managing Director of Solo Containment.

Paul Gurney-Read has been assisting pharma and chemical industry clients for the last 18 years with the development of global material handling strategies, facility capability audits and containment projects from concept design through to equipment testing and operator training.

Contact:

paul@gurney-read.co.uk www.solocontainment.com