Danger in the Bottling Plant

In the UK, the noise level in bottling plants which requires employers to make hearing protection available to workers is 80 dB, and the level at which workers must wear hearing protection is set at 85 dB.  The Control of Noise at Work Regulations 2005, which come into force on 6 April 2006, require employers to do the following: assess the risks employees face from noise at work; take action to reduce noise exposure that produces such risks; provide employees with hearing protection if the noise exposure cannot be reduced sufficiently by other methods; ensure that legal limits on noise exposure are not exceeded; provide employees with information, instruction and training; and conduct health surveillance where there is a risk to health.

The Health and Safety Executive (HSE) has produced a free leaflet that provides useful information on a number of areas, including: how loud noise can damage hearing; how to assess and control noise at work; different types of hearing protection; when to inform and consult workers; and health surveillance.

Chemicals are often another of the major hazards to be found in a bottling plant and working with chemicals requires a risk assessment. Risk assessments, training in chemicals handling and COSHH issues should be provided by your supplier as part of the service.  Manual handling of chemicals creates a high potential risk, however dangerous handling of chemicals can be avoided by use of suitable proportioning and dosing devices, a range of which is available from several suppliers.

Hydrogen Peroxide or Peracetic Acid?

In the bottle wash process, peracetic acid is often used as terminal disinfectant before the final water rinse.  The reasons for choosing peracetic acid are well known, such as excellent activity gainst bacteria, spores, yeasts and moulds, a reasonable price (particularly for larger quantities), good efficacy even at low temperatures and harmless decomposition products (vinegar and water). Although, there has been some concern that if not rinsed adequately, vinegar could act as a bacterial nutrient.

However, if you have a concern about your chemical effluent and normally have to use special facilities to cope with it, hydrogen peroxide is the friendliest terminal disinfectant to use.  The breakdown products are water and oxygen, so, if released into ground water, they will actual have a beneficial effect by oxygenating the ground water.

Hydrogen peroxide is used at a similar concentration to peracetic acid and the efficacy against bacteria, yeasts and moulds is the same, with just a slight reduction in effect on bacterial spores. Pricing is not as different as you may imagine.  Normally, bulk hydrogen peroxide is sold as a 35% concentrate, whereas peracetic acid is normally delivered at 5%, hence although the drum price is very different, dilution of hydrogen peroxide down to the use concentration will easily offset the higher drum price.

Peracetic acid and hydrogen peroxide are commonly available from several suppliers.

Sell-By Dates for Chemicals

I have been asked by several customers about sell-by dates related to chemicals. This depends on the type of chemical. Products based on detergents and water softeners, for bottle washing, and descaling chemicals have a very long shelf life because generally there are no unstable elements in the formulations.

Shelf-life becomes more of an issue when oxidising disinfectants are considered such as peracetic acid and hydrogen peroxide-based disinfectants. These materials are inherently unstable (that is partly why they work well as bacteria killers) and require stabilizers in the formulation to lengthen the shelf-life.  Care should be taken in storing these materials so that the decomposition is not accelerated.

Conditions which can accelerate this are: excessive heat and light and contamination. The golden rules are therefore to store in a cool place and out of direct sunlight. The caps should never be left off, to prevent any possibility of contamination from the surroundings.

Most of these materials will retain there potency for over one year, but this is very dependent on storage conditions. The decomposition will occur slowly but gradually during the year, so if you have older stock it may be necessary to check concentrations in use and, if necessary, increase the concentration slightly to compensate for any loss. 

How to Wash Polycarbonate Bottles Without Stress

I have written about micro-cracks in polycarbonate bottles previously, but it is worth going into more detail here because this phenomenon can be avoided.  The consequences of not being aware of micro-cracks can be leaking bottles and contamination of water with unfiltered air while the bottle is on the cooler.

Polycarbonate bottles are produced using the extrusion blow moulding process in which a tube of hot plastic is extruded between two open halves of a mould.  When the tube, or parison, reaches the proper length, the mould halves clamp together and air is injected to force the parison to the shape of the mould.

Cooling water is then circulated inside the mould halves to cool the plastic until it is rigid.  The mould opens, the part is ejected, any excess flash is removed, and the bottle is almost ready for use.

The need for a high production rate dictates a rapid cool-down following the blowing operation.  Unfortunately this creates areas of unequal stress in the plastic, particularly at the clamping points where the mould comes together.

Bottle producers relieve the stress by re-heating the bottle to just below the softening point of the plastic and then allowing it to cool slowly.  If done properly, this succeeds in removing most of this induced stress.  If hurried, some of the stress remains.

The bottles then can easily form micro-cracks when subject to further stress.  This may be from the use of incorrect bottle-wash chemicals, the bouncing movement of bottles in the delivery truck, stress of pressurising during the filling operation or use of badly designed bottle racks.  The older the bottle, the more likely micro-cracks will appear.

These cracks are sometimes difficult to see (see the microscope view).  However, when the bottle is inverted on the cooler, after drawing water, a vacuum exists briefly and air can enter through the micro-cracks as well as through the filter.  Bacteria and algal spores also enjoy the haven of the micro-cracks during bottle washing.

Stress cracking with the wrong kind of detergent can can occur rapidly and reduce the number of viable wash cycles of the bottle while encouraging algal growth ("green bottles").  Test rigs can easily demonstrate the results of chosing the wrong bottle-wash detergent (see photo showing broken polycarbonate strips).

 Various bottle-wash detergents are available on the market that are specially formulated to avoid stress cracking of polycarbonate while ensuring a clean bottle.