John Farrell Hughes

Interaction of air ions and bactericidal vapours to control micro-organisms

Aims:  The aim of this study was to investigate the antibacterial activity of candles containing specific‐antibacterial compounds, such as essential oils and their constituent compounds. The importance of the ionization products from the flame and the aerial concentration of the volatile compounds were investigated.

Bactericidal Effects of Negative and Positive Ions Generated in Nitrogen on Starved Pseudomonas Veronii

Abstract Bacterial cells in natural populations are rarely at exponential phase due to insufficient availability of nutrients. Suppression of cell division due to starvation is one of the most common forms of initiating stationary phase. Once initiated, cells at stationary phase are considerably more resistant to a host of challenges. The bactericidal effect on stationary phase cells of both negative or positive ions generated by a d.c. electrical corona in nitrogen was investigated. Bioluminescent Pseudomonas veronii cells, resuspended in sterile water and starved for 24 h , were inoculated onto aluminium foil coupons (2 cm 2 ) and placed into a custom-built multi-point-to-plane ion generator situated within a plastic chamber. Under a nitrogen atmosphere the coupons were exposed to either negative or positive ions for various time periods. Following exposure, cell viability was determined by the measurement of light output recorded from foil coupons using a luminometer and converted to colony forming units per millilitre. Exposure to either negative or positive ions produced significant reductions (p

Dust anchoring characteristics of electret fibres with respect to Der p 1 allergen carrying particles.

The avoidance of house dust mite allergens is a major area of interest and essentially requires a significant removal of these allergens from the immediately respirable air. Electrostatic attraction and anchoring of particulate matter using electret polymers is commonly used for air filtration purposes. This effect is investigated for its possible use in domestic allergen avoidance. Polypropylene electret, heat-treated electret and non-electret, and wool and nylon fibre samples were soiled with house dust known to contain Der p 1 allergen. These samples were vacuumed at three air face velocities. The proportions of released and anchored dust were calculated. Released dust was collected and analysed for Der p 1 concentration and compared to stock dust values. Results showed that compared to uncharged fibres at least 95% more dust remained anchored in the electret fibres. Also, overall Der p 1 release was reduced by more than 49%. Der p 1 allergen concentrations in the collected dust were relatively constant for all the fibres tested, indicating no selective attraction or repulsion of Der p 1 allergen carrying particles in the experimental dust. The consistently high dust anchoring ability of the electret fibres could be used in many domestic products that are known to harbour particulate allergens, to reduce their release and inhalation.

Electrostatic Deposition of Charged Insecticide Sprays on Electrically Isolated Insects

Electrostatic charging has been used to improve targeting and efficacy of agricultural sprays for decades. However, the benefits of electrostatic deposition have not been exploited for the control of flying insects in the domestic environment. The work described here demonstrated that electrostatically charged sprays significantly increase deposition onto electrically isolated insects (R > 100 GOmega), and that this translated into improvements in bioefficacy in direct spray bioassay experiments. The time taken to knockdown 50% (KD50) of the houseflies was reduced from 2.63 to 1.98 min by increasing the charge-to-mass ratio of the insecticide spray from 2.66 x 10(-5) to 2.16 x 10(-1) C/kg, the difference being statistically significant (p = 0.043). This increase in bioefficacy remained during space spray bioassays when living room furniture was present in the test chamber. Here the rate of KD50 was increased from 7.30 to 5.60 min by increasing the charge-to-mass ratio of the insecticide spray from 2.66 x 10(-5) to 2.16 x 10(-4) C/kg, with the difference being statistically significant (p = 0.044). Electrodeposition occurred despite electrical isolation of the target insects and consequent absence of a conductive path to earth. Improvements in the bioefficacy of charged insecticides over uncharged equivalents arise through the attraction of charged droplets onto insects in flight and through space charge effects causing improved dispersion of the aerosol in the chamber. Any increase in deposition of the charged aerosol onto walls, ceilings and items of furniture does not counteract the improved bioefficacy.

Long‐range destruction of Der p 1 using experimental and commercially available ionizers

Background To reduce the risk of sensitization and the elicitation of allergy symptoms, it is important to reduce the level of allergens in the home. It has previously been demonstrated that corona discharge, the process by which ionizers produce ions, can destroy the major house dust mite allergen Der p 1.

Electrostatic charge characteristics of Der P1 allergen carrying particles and the house dust mite, Dermatophagoides Pteronyssinus.

Control of the house dust mite allergen has received considerable attention owing to its importance in some allergic diseases. One aspect of dust mites and their allergen-carrying faecal particles that has not been reported on, which may have allergen control applications, is the electrostatic charge they carry in the natural environment. To promote tribo-electric charging, household dust containing dust mite allergen and live house dust mites are separately agitated while in contact with either polypropylene, nylon or earthed metal. The charged dust and mites are subsequently subjected to electrostatic separation and collection. Results for concentrations of the house dust mite allergen, Der p1, indicate that, when subjected to nylon, Der p1 carrier particles appear to be predominantly positively charged. Similarly, when subjected to polypropylene, Der p1 carrier particles also appear to be positively charged. Reduction of excess free charge by agitation against earthed metal does not appear to affect the observed charging characteristics, indicating that the positive charge may be bound or inherent in the Der p1 carrier particles. In contrast, house dust mites exposed to nylon appear to be generally charging negative, whereas mites exposed to polypropylene appear to be charging positive. The observed electrostatic characteristics of the mites and Der p1 carrying particles will be useful in the future development of electrostatic allergen control methods.

Powder coating - corona versus tribo charging

Abstract Both corona and tribo techniques have been adopted for particle charging in the powder coating industry. Although corona offers a relatively controllable charge source, the mechanism is inherently inefficient in terms of imparting charge to airborne particles. In addition, the highest density of free ions and high electric fields have been shown to be detrimental to good deposition. Tribo-charging offers some advantages, but is notoriously unpredictable. Many of these operational difficulties may be overcome by combining internal corona augmentation with primary tribo-charging. Free ions are eliminated, no high field exists between gun and workpiece and the tribo-charging characteristics are retained for prolonged periods of operation.

Electrostatic Hazards Associated with Powder Handling in Silo Installations

Pneumatic delivery and general movement of powdered products inevitably results in some degree of charge separation between the product and its containing walls. Unlike electrostatic charging associated with high-velocity pumping of insulating liquids, where addition of an antistatic additive is a standard means of quenching the charge, the situation is a little more difficult to control with powder. There is as yet no antistatic additive commercially available for powders, and therefore the standard procedure of grounding all plant hardware does not give sufficient protection against charge accumulation. The powder itself, will still emerge at the end of the delivery sequence in a highly charged state, and it is this which usually results in a potentially hazardous situation. A case study on a powder handling silo installation following a severe explosion during filling operations is described.

Elimination of Electrostatic Charging in Punctured Aerosol Cans

A hazard situation during normal can-filling operations on pressure-packed container products is described. Under certain conditions and with certain products, accidental damage to the container resulted in charge separation between the container and the product being expelled under pressure. The cause of electrostatic charge separation was investigated, together with identification of the product component responsible for the charging. Methods of eliminating the charging are detailed, and various additives which were capable of maintaining the charging to acceptable levels were isolated. Recommendations for safe plant operation, in terms of electrostatic charging of damaged cans, completes the investigation.

Electrostatic Targeting for Allergen Removal and Pest Control Applications

Today. in the United Kingdom, approximately one in seven infants are diagnosed with asthma in the first six months of life. There has been a dramatic increase in recent years, and asthma-related drugs now account for approximately 11% of the total prescription costs to the National Health in the UK (Department of Health, Asthma and Epidemiology, HMSO, 1995). In addition to medication, preventative measures include attempts to exclude the allergen from the domestic environment. This requires careful control of the most common asthma allergen, Der p1,which is conveyed by the waste products produced by the house dust mite (Dermatophagoides pteronyssinus). Acaricides may be used to kill the dust mites,but these have to be combined with allergen denaturing agents if eradication of the allergen is sought. Mechanical barriers such as mattress and pillow covers offer some protection from contact with the allergen, but often with a varying degree of success. High levels of allergen carriers are also known to exist in carpeting, and this can lead to a particularly undesirable environment for infants who frequently crawl with their faces close to, and sometimes in contact with, the carpet pile. Inhalation of allergen is usually unavoidable in this situation. Research has indicated that the use of electret fibres can dramatically enhance the anchoring of allergen carriers in the carpet pile. Electrostatic adhesion of the carriers to the electret fibres ensures that for normal traffic conditions, such as walking, crawling, playing etc, much less dust is released from the carpet; thus reducing the probability of inhalation. Dispensing domestic products in aerosol form has undoubtedly been a commercial success; offering considerable consumer advantages in applications ranging from paints, polishes and insecticides. The targeting of products in aerosol form may not, however, be optimised with a high proportion of the product often missing its target. It is well known that electrostatic spraying can enhance targeting, but this technology is normally limited to industrial processes such as paint and powder coating. A novel and unique aerosol package has been developed which charges the aerosol on delivery in a controlled manner. The Smartseeker-(-Smartseeker is a trademark of Reckitt Benckiser) insect seeking technology is now incorporated into a commercial aerosol insecticide, and is the worlds first electrostatically optimised aerosol can which requires no active energy source. Flying insect knock-down is enhanced by up to 34% with this technology.