Characteristics of Ultrafine Particles
Transport and Fate in the Environment
Prevention or Control of Exposures
Human Health Effects of Ultrafine Particles
Absorption and Distribution
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PREVENTION OR CONTROL OF EXPOSURES
Exposures to UFPs is typically an issue related to environmental exposure, howver, occupational exposures can also occur which have the ability to adversely impact human health. The following is a discussion regarding potential control technology strategies in order to reduce or eliminate UFP emissions.
Vehicle and Industry
Generally, the control strategies used to address UFPs requires the development of an apportionment of UFP generation from the various emitters and the generation of control methods designed to reduce the overall UFP concentrations in the ambient air. Air control technology for UFPs includes such devices as diesel traps, (Abdul-Khalek et al., 1998), fuel reformlations and changing the patterns of transportation behavior including public transit.
Epidemiological studies have consistently found an association between small increases in urban particulates and health effects, including increased morbidity and mortality in people with respiratory and cardiac disease.
The observed effects are associated with the fine rather than the coarse particles in the atmosphere. Moreover, animal studies have shown that ultrafine particles have a significantly greater pulmonary inflammatory potency than larger submicronic particles.
A recent epidemiological study found that particle number - reflecting ambient ultrafine particles - correlated better than fine particle mass with increased symptoms in asthmatics. These results form the basis for the ultrafine particle hypothesis.
The proposed pathophysiology for pollutant-induced lung inflammation involves the following sequence of events:
- Injury to epithelial cells by reactive oxygen species, possibly enhanced in the presence of metals via Haber-Weiss and Fenton chemistry, accompanied by activation of nuclear regulatory factors, leading to elaboration of proinflammatory cytokines, including interleukins-8 (IL-8) and -6 (IL-6), and increased expression of nitric oxide synthase (NOS), with increased nitric oxide (NO) in exhaled air.
- Activation of vascular endothelium and circulating leukocytes. Emigration of inflammatory cells from blood to tissue sites involves up-regulation of adhesion molecules and other markers on vascular endothelium and on circulating leukocytes.
- The events in the process of leukocyte-endothelial binding include
- increased expression of adhesion molecules followed by shedding of adhesion molecules as cells "tether and roll",
- leukocyte activation,
- stable adhesion, and
- Transmigration through the epithelium.
Platelets become activated and adhere to endothelium and leukocytes. Endothelial activation may further contribute to the increase in exhaled NO concentrations seen with airway inflammation. (iii) Increased release of IL-6 and tissue factor by activated blood mononuclear cells. Interleukin-6 initiates hepatic synthesis of acute phase proteins, including serum amyloid A (SAA), fibrinogen, and plasminogen activator inhibitor-1 (PAI-1). Monocyte tissue factor and endothelial cell activation initiate the coagulation cascade, as reflected by the presence of D-dimer, soluble fibrin, and prothrombin1+2. (iv) Possible adverse cardiac events in patients with critical coronary lesions, as a consequence of increased blood coagulability, platelet activation, and endothelial dysfunction.
The requirement of using less hazardous substances and processes is a core element of various directives and orders.
1. Measurements technology in general;
2. Tracer gas technology;
3. Determination of dust levels;
4. Test benches; and,
5. investigations using models and standardizations.
Requirement which can indeed lead to a considerable reduction in risk, as it starts off at the very source.
As far as aerosols are concerned, two types of dust production can be distinguished.
1. A product placed on the market is not in compact but in dust form.
2. Dust is generated during product processing, e.g. during cutting, grinding or by chemical or thermal reaction, or the particle size distribution changes as a result of processing, as for instance in the case of milling.
Companies have difficulties in estimating whether or not, in terms of quantity and fineness, the occurring dust (ultrafine particles) is hazardous for the employees and if so, how high the risk potential is:
Protective measures, the scope of atmospheric limit values for particles and the possibilities of detection of hazardous aerosols and ultrafine particles call for harmonized definitions and conventions or standardized approaches. Implementing scientific concepts correctly and applying occupational health and safety provisions in a targeted way.
1. To ensure that less dusty substances and processes are used, it is necessary to provide companies and supervisory bodies with information on and instruments for risk assessment.
2. Information on the substance-inherent risk (substance database) and on the probability that certain substances occur in connection with defined workplace situations (exposure scenarios) and standardized characteristics relating to the dustiness of products with use of protective measures.
Reducing hazards from exposure to wood dust in the work environment
In the construction industry, the carpentry sector is directly concerned by the reduction of exposure to airborne particulate contaminants.
Woodworking produces significant dust emissions that, unless properly collected, can generate very serious occupational diseases such as carcinoma of the frontal sinuses with irritation.
Simple rules that can be followed include :
1. Keep tools properly sharpened
2. Capture dust as close as possible to the source of emission
3. Assess the fan flow rate required according to the number of machines operating simultaneously
4. Reduce pressure drops in the exhaust system
5. Avoid dust deposits in ductwork " Connect the on-off of the suction nozzle to the start and stop buttons of the machine concerned
6. Install the machines requiring the highest flow rates as close as possible to the main dust collectors
7. Locate fan and filter bags outside the workshop
8. Modify work practices
9. Maintain the equipment in good working order.
10. The type of exhaust equipment should be chosen according to workshop characteristics.
11. Certain items of equipment such as band grinders or portable machines are particularly important sources of dust emission. Whenever possible, they should be isolated from the remaining zones of the workshop.
12. Personal protective equipment be used as a last resort.
Using the new workplace ventilation systems
The term ventilation system covers devices for the capture of hazard substances at the source of emission and systems for workplace ventilation (indoor ventilation). The capture of emitted pollutants is aimed at preventing the presence of hazardous substances in breathing air.
- To improve capture efficiency, the exhaust hoods should be replaced by modern highly-efficient exhaust systems. The latter take account of particular fluidic effects.
- Air flow patterns (supply air flow patterns) for the entire room play a central role in this respect.
An efficient air flow pattern aims at avoiding the spreading of hazardous substances all over the room and at making sure that hazardous substances emitted into the workplace air are removed safely and effectively. This principle also applies to other substances like smelling irritating agents as well.
Use Of Air Filters
Air filtration is a technique widely used for removing airborne particles, both in industry and the tertiary sector. Filters can be components of collective and personal protective equipment such as industrial dust collectors and respirators. Their performance must be known to guarantee both the quality of air in working environments and the protection of workers.
Determination is essential for dust collector design (choice of filter media and unclogging technique according to dust properties/ultrafine particles) and for the control of the filter equipment in operation.
Metalworking fluids (MWFs) are essential process materials for any kind of metalworking and metal treatment application. MWF aerosol and vapor emissions into the work space are usually limited by machine enclosures as well as suction plants. 90 of the systems installed recirculate ventilated air back into the work room after demisting.
Preventing the process from becoming a serious source of airborne MWF exposure itself requires high-performance filtering systems. The aim of this work was to investigate changes in demister performance with maintenance time.
It is clear that only an integrated approach which includes measures covering the complete process configuration can meet occupational health and safety requirements within economic limitations.
Rock humidity on dust content and development of efficient technical measures for dust control in open-cast mining
This simple process of moistening the rocks can limit the exposure of the ultrafine particles to a fine extent. It is a simple and inexpensive way of doing things and contributes a long way in the integrity of worker and workers health simultaneously.