DGUV Information 213-854 - Nanomaterials in the Laboratory Tips and Handling Inf...

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Abschnitt 2, Protective measures
Abschnitt 2
Nanomaterials in the Laboratory Tips and Handling Information (DGUV Information 213-854)
Titel: Nanomaterials in the Laboratory Tips and Handling Information (DGUV Information 213-854)
Normgeber: Bund
Amtliche Abkürzung: DGUV Information 213-854
Gliederungs-Nr.: [keine Angabe]
Normtyp: Satzung

Abschnitt 2 – Protective measures

Exposure by inhalation

Ventilation system measures

The use of standardised and tested laboratory fume hoods is an effective protective measure here. With extremely dangerous nano-materials (e. g. those created from highly toxic materials or which are highly spontaneously flammable), glove boxes, glove bags or sealed equipment can also be used. When working in a fume hood, it is vital that the sash be (largely) closed. Formation of dust can be prevented by using nanomaterials in a wet rather than dry form (suspensions, colloidal solutions, pastes). Integration in matrices (granules, compounds) is also helpful. However, if a situation requires dry, non-compound nanomaterials to be used, as little mechanical energy as possible should be applied, as this can often lead to agglomerates breaking up and free nano-objects thereby being released into the air. Extraction systems with excessive flow rates can cause significant units (not just nanoparticles, but also larger objects) to be carried out in the exhaust air stream. It is therefore not recommended to work near the open sliding front window in fume hoods. If the window is open, even small air movements can cause particles to escape. When it is (largely) closed, this leads to high air intake speeds near the gap on the sliding front window, which can cause particles to be transported. Investigations into fume hoods in the US have shown a kind of outbreak behaviour of nano-objects, although results in Germany (tests on a fume hood as per DIN 12924-1 with several nanomaterials) were unable to confirm this. A large containment capacity was observed here. Fume hoods generally have a divided sash that makes it possible for the user to reach in from the side if necessary, which significantly increases the retention capacity of fume hoods compared to that of raised front sashes (Fig. 3).

Fig. 3 Fume hood with work performed through the divided sash

Large equipment

Large equipment, such as tube furnaces for manufacturing, should ideally not be operated in the fume hood, as they disturb the air flow. If such equipment is set up next to the fume hood, the reaction tube can be laid through the wall of and into the fume hood, thereby allowing extraction via the fume hood. If equipment of this nature really needs to be set up within the fume hood, it is vital that sufficient distance from the inner surfaces of the fume hood be provided to ensure that the air streams are impaired as little as possible. A distance of at least 5 cm from the working area in particular should be maintained (Fig. 5).

If large equipment has to be operated in the fume hood, inspecting the air flow with a smoke tube or smoke generator provides valuable information about possible disruptions or even emissions from the fume hood. Small handheld, battery-operated smoke generators have proven useful for these inspections (Fig. 4).

Fig. 4 Testing the fume hood with a smoke generator

Fig. 5 Furnace placed on spacers - the apparatus is equipped with a rinsing line

Closed systems

Where possible, nanomaterials that have a tendency to give off dust should be handled in closed systems if they cannot be handled safely in a fume hood. Working methods of this kind are similar to those commonly practised when handling air-sensitive or moisture-sensitive compounds in the lab. Powdery nanomaterials can be moved from one container to another without any leakage using curved glass tubes (Fig. 6). With the help of a special Y-piece, a glass spatula can also be used for measuring out substances (Fig. 7). Apparatus can be filled, either in portions or virtually continuously, using glass vessels or - a particularly elegant solution - hand-operated (Fig. 8) or automatic (Fig. 9) powder dosing funnels. Pre and post weight measurements can be taken in the corresponding parts of the equipment in the fume hood, in the weighing chamber or in the glove box, precluding the risk of any exposure. The grinding bowls of a mill can be removed and transported in a sealed state, with the contents only being removed later in a fume hood or in the glove box (Fig. 10). Spraying of particles can be countered by preventing electrostatic charges (Fig. 11).

Fig. 6 Transfer bow for powders protected from draughts (if necessary inert gas - Ar to be preferred - can be used to protect the powder against moisture and air)

Fig. 7 Transfer with a glass spatula protected from draughts (if necessary inert gas - Ar to be preferred - can be used to protect the powder against moisture and air)

The powderous material can be added without the need to open the apparatus (Fig. 7, Fig. 8). The powder dosing funnel can be filled in the fume hood and also cleaned there.

Fig. 8 Manual powder dosing funnel on a three-necked flask

Fig. 9 Automatic powder dosing funnel on a three-necked flask for constant dosing over long periods of time

Fig. 10 Ball mill with closed grinding bowl

Fig. 11 Balance with electrostatic discharging equipment (U-electrode)

Encapsulated dosing systems (automatic scales) are very well suited for quick, low-exposure weighing (Fig. 12).

Fig. 12 Encapsulated scales with automatic dosing head

Fig. 13 Glove box with airlock

Fig. 14 Glove bag with closing clip for feed opening

A high level of protection is also achieved by working in a glove box (Fig. 13), or alternatively in a glove bag (Fig. 14), which can then be disposed of with no risk of contamination. Where necessary, the glove box also provides especially good protection against airborne influences on the nanomaterial (hydrolysis, oxidation, potential self-ignition) by providing a particularly clean inert gas atmosphere. A glove bag can also be rendered inert, however it is less impermeable to air.

Cleaning equipment

If the apparatus needs to be dismantled, for example for cleaning, it should be well rinsed before any of its contents can escape into the air in the lab. This is easy to arrange if corresponding (lockable) connections were included for rinsing lines when the system was conceived and set up (Fig. 5). Alongside any necessary connections for inert gases, these can be connections for the supply and draining of cleaning fluid, although water is generally enough here. The drained liquid can then be collected as waste in a dedicated container. When setting up the apparatus, it is important to ensure that the rinsing fluid can reach all parts of the system in which nanomaterials may be located. To prevent a pressure build-up due to evaporation of the rinsing fluid and also stress fractures, the equipment should not be rinsed at elevated temperatures. The risk of dangerous reactions between the contents of the equipment and the rinsing fluid must also be eliminated. As such, it will not be possible to use water in all cases.

Ventilation issues

If devices are to be connected to an extraction system to reduce the risk of exposure, this can also take the form of an enclosure or extraction at the source of the emissions. Here, it is vital to ensure that extraction is as complete as possible, that the speeds of the air stream in the area of the extraction system are not high enough to cause vortexes to form and also that fractions of nanomaterials that move easily are carried along by the air stream. Expert design of the extraction apertures is necessary. Simply positioning an exhaust hose near the point of emission will generally be of little use or even have a potentially negative effect. For these two reasons, even in laboratory fume hoods the air intake volume flow should not be set too high. The values set for the exhaust air volume flow (as a result of the type approval test) should also not be increased at random for "apparent safety reasons". Nano-objects carried in the air stream can be deposited in the exhaust air systems (largely behind the extraction system's deflection wall or in exhaust channels, particularly in corners and bends). When performing maintenance work, appropriate consideration must be given to the health and protection of all persons working on the system, as well as to potential contamination of the area.

Because of the airflows that are constantly present in fume hoods, deposited nanomaterials can permanently release free nano-objects even if they are not currently being handled. Contamination on tables near airflows can also exhibit such an effect and release nano-objects into the laboratory atmosphere. The accumulation of dust should therefore be avoided.

If nano-objects genuinely need to be released in a room, respiratory protection must be worn. Class P2 or P3 particle filters are effective here. When releasing such particles into the air, appropriate consideration must of course also be given to contamination of the room.

If nanomaterials in solution or suspension are spilled they have to be removed before they get dry and possibly airborne.

It is difficult to assess the toxicity of nanomaterials in group IV. Unless it has been proven that the fibres of such a nanomaterial do not meet the WHO fibre criterion, asbestos-like effects cannot be ruled out. Appropriate minimisation through protective measures and special care when working are required. It is not possible on principle to work openly with the nanomaterial in the laboratory. Contamination of the room would necessitate particularly costly cleaning measures. Such measures are to be specified in advance. Rigid fibres in particular require special attention. Materials in group II also require careful, low-exposure handling. The use of fume hoods, glove boxes, closed apparatus or similar secure facilities is necessary. It is recommended that you inspect the airflow conditions in and, if necessary, in front of the fume hood using a smoke tube or smoke generator, as disruptive airflows in the room when the fume hood is open can cause the atmosphere inside the fume hood to escape into the laboratory room.

Nanomaterials in group I can be assumed to have little or no potential as a toxic hazard, provided that the material itself does not exhibit toxic properties. It must be kept in mind, however, that even though these nanomaterials could be handled openly because the concentration limit of the evaluation benchmark has not been reached, there remains a residual uncertainty concerning the effect of materials that have not been investigated sufficiently. The classification only concerns toxic effects. Other effects - particularly fire and explosion risks - are not considered. Even materials that are proven to be harmless to people may still contaminate the room, which can impair testing or measuring results, for example by affecting blind values.

Nanomaterials in group III should be handled in such a way as to keep the risk of exposure to a minimum. Announcement 527 on Hazardous Substances recommends using half the occupational exposure limit (relative to the currently applicable legal workplace limit for the alveolar dust fraction according to Technical Rule for Hazardous Substances 900) as an evaluation benchmark. The evaluation benchmark should not exceed 0.5 mg/m3 (at a concentration of 2.5 g/cm3).

Dermal and oral exposure

Skin contact

Gloves should always remain in the fume hood (or any other potentially contaminated work areas). Contamination on the sleeves of lab coats can be avoided by using cuffs that can be pulled over the sleeves. These should then also be left in the fume hood. Alongside protection from exposure by inhalation, protection from dermal and oral exposure is also necessary. Gloves should not have any openings (due to poor quality, ageing or damage). If solvents are used in production or use of nanomaterials (e. g. in suspension) the protective gloves must be qualified to withstand the solvents.

Oral intake

Airborne nano-objects are not only inhaled, but can also deposit themselves slowly onto surfaces. This also applies to the agglomerates and aggregates which nano-objects form at varying rates with one another or with larger particles suspended in the air. From the skin on the face, these can then find their way into the digestive tract via the mouth. This can be caused by a lack of proper hygiene practice (e. g. scratching the forehead with contaminated gloves).

Checking the effectiveness of the measures

Measurements

Measurements can be helpful in assessing the situation, although issues such as the often high biogenic and anthropogenic background pollution with nano-objects and the lack of a quantitative judgement basis make this difficult. When working in the lab, however, taking measurements while performing tasks can provide useful statements regarding exposure. Portable or hand-held devices are available for this. Swipe samples or measurements with dust collectors, on the other hand, provide only limited useful information on nanoparticle exposure. There is a widely agreed upon graded measurement strategy available for any measurements that need to be carried out, which reduces what can be a considerable amount of work to a degree appropriate to the relevant exposure.