Abrasive Cleaning and Water Jetting

Introduction

Included in the definition of construction work is maintenance "which involves the use of water or an abrasive at high pressure". Abrasive cleaning or water jetting will therefore be subject to the requirements of CDM if the basic criteria for application of the regulations are met.

Both abrasive cleaning and water jetting have a number of applications, including the cleaning of masonry, the removal of coatings in preparation for new painting or resurfacing work, sewer cleaning, and the removal of bird excrement. Methods can vary but both operations can present a significant risk to contractors and employees. In addition to health and safety issues consideration should be given to the environmental impacts of any cleaning operations.

Those with responsibility for hiring contractors to undertake this type of work should have a sound understanding of the risks involved and the control measures needed. Contractors should have knowledge of the Water Jetting Association's Code of Practice and also of BS627: Code of Practice for Cleaning and Surface Repair of Buildings.

What is abrasive cleaning and water jetting?

Abrasive cleaning methods include all techniques that physically abrade the building surface to remove soils, discoloration, coatings etc. Such techniques involve the use of certain materials that impact or abrade the surface under pressure, or the use of abrasive tools and equipment.

Sand is probably the most commonly used type of grit material, ( others include crushed walnut or almond shells, rice husks, ground slag, synthetic particles, glass beads and microballoons. These techniques are known as "dry grit" methods.

"Wet grit" methods combine water with grit as an abrasive cleaner. One technique involves the addition of a stream of water to a regular sandblasting nozzle. In a second technique, a very small amount of grit is added to a pressurized water stream.

High pressure and ultra high pressure water jets are frequently used to remove surface coatings in cleaning operations and even for cutting work. A lance is often used to manipulate a water jet that abrades the surface area.

Hazards

Typical hazards will include the following:

• Inhalation of dust from the cleaning process
• Injection of particles and debris into the skin
• Contact with discharged grit particles or water jets
• Flying debris from the work surface
• Electrical shocks from the plant used
• Working in confined spaces when water jetting drains and sewers
• Falls from height eg when cleaning facades
• Exposure to noise and vibration

The potential for environmental damage should be considered as dry gritting can create a considerable amount of dust, polluting the environment around the job site and resulting in deposits of dust on neighbouring buildings, parked vehicles, and nearby trees and landscaping.

Wet grit methods can deposit slurry at the base of buildings and high pressure wet cleaning can cause damage by affecting interior materials such as plaster, joist ends and metal building components.

The equipment used can cause noise and vibration, resulting in distress to those occupying the premises where the work is taking place and those working in neighbouring premises.

Water jetting machines use large volumes of water (up to 60 gallons per minute) and generate a significant quantity of waste water. If the water is contaminated by the operations, disposal to a foul sewer may require a "consent to discharge" from the sewerage undertaker (water company). The client should seek further advice from the water company's trade effluent officer.