Dust

Introduction

Dust is generated in many ways during construction and can give rise to health problems through inhalation, or contact with the skin or eyes. Control of such dust is now required under the Control of Substances Hazardous to Health Regulations 1999.

Such dusts can be divided into five categories dependent upon their biological action

• Inert dusts - they accumulate in the body but produce no reaction: however should they enter the lung they can impair lung clearance by obstructing the lymph flow.
• Toxic Dusts - these are usually metal compounds such as chromates or Lead compounds which may have chronic or acute effects on various organs of the body.
• Fibrogenic Dusts - these affect the lungs and cause conditions such as pneumoconiosis and are the most dangerous forms of dust.
• Allergenic Dusts - these may cause asthma or eczema and the effects may vary from person to person. It is possible for a person to become sensitised to a particular substance and be affected by it after being exposed to it for many years with no ill effects.
• Abrasive Dust - Any or all of these types can be abrasive and have detrimental effects on the eyes especially to a growing number of people who wear contact lenses.

Identification

It is important to identify substances and processes which give rise to harmful dusts in advance so that they can be designed out or an alternative substance specified or so that precautions can be taken to mitigate their effects. This is the approach taken by the COSHH regulations which require assessments be made of all hazardous substances. Suppliers of all substances are required to provide details of their characteristics so that harmful ones can be identified in advance and perhaps replaced by a less harmful one.

Similarly processes which give rise to harmful dusts can be designed out or less harmful methods used or precautions be taken to lessen the effects.

Dust control

The basic methods of dust control on a construction site are:

• Substitution by a less harmful alternative substance or process.
• Application of moisture to prevent dust from becoming airborne.
• Segregation of the dust generating processes.
• Ventilation.
• Extraction.

Substitution

An example is that in the UK the use of sand for sand-blasting is prohibited in most cases and some other less toxic material used in its place. The scabbling of concrete generates silica dust and should be avoided where possible.

Moisture

Wet methods can be used effectively to prevent dust. However water must be applied before the dust is generated as attempting to control dust already in the air by means of water spraying is ineffective. Some solid materials such as sandstone can be made to soak up water so thoroughly that that no dust is generated during subsequent cutting operations. It must be noted that the correct degree of wetting must be achieved before processing and the treated material must not be allowed to dry out.

Segregation

It may be possible to segregate operations or processes which generate dust so that its effects are mitigated. An example would be the setting up of a timber processing shop on a large site so that dust generated during sanding and sawing operations is separated from the rest of the site.

Ventilation

Dust can be collected at source by the provision of efficient exhaust ventilation. Examples are found on some portable tools and the main criteria is that the dust is collected as close to the source as possible.

Explosions

Whether or not a dust is explosive is dependant on the substance, the particle size and the concentration of dust in the atmosphere. Most common substances which are combustible such as wood dust can become explosive but mineral dusts, being non combustible, cannot.