Number

152-EN

Section

General Section

Use

Abstract

Facade cleaning may be performed with chemicals or by using blasting with various media. Chemical cleaning is often done with hazardous substances like dichloromethane or methyl pyrrolidone. Sandblasting is hazardous due to the crystalline silica, a carcinogen. Using dry ice blasting may be a safer alternative. An example of its use in restoring ancient Prague monuments is presented.

Substituted substances

Alternative Substances

Reliability of information

Evidence of implementation: there is evidence that the solution was implemented and in use at time of publication

Reason substitution

CMR

Hazard Assessment

Substances to be substituted: Dichloromethane is a Substance of very high concern and is included on the REACH restriction list, according to Article 73 of Regulation (EG) No. 1907/2006. (REACH Regulation). 1-Methyl-2-pyrrolidone is a Substance of very high concern and is included on the REACH restriction list, according to Article 73 of Regulation (EG) No. 1907/2006. (REACH Regulation). Quartz is a group 1 carcinogen (IARC) as listed in the Substance Database according to SUBSPORTplus Screening Criteria (SDSC). The substance has no harmonised classification according to Annex VI of Regulation (EC) No 1272/2008 (CLP Regulation). However, it has a recognized carcinogenic effect which is recorded in the TRGS 900, An EU limit BOELV: quartz (alveolar): 0.1 mg/m³ (2004/37/EC) and in Germany. 0.05 mg/m³. Alternative substances: Though carbon dioxide is not toxic leakages in confined, unventilated spaces may be hazardous due to oxygen replacement. Carbon dioxide is a greenhouse gas and unless it is generated as by-product or recovered from a natural source, the technology may be considered to increase the company's carbon footprint.

Description of Substitution

Cleaning facades of historical monuments requires care for the original material and efficiency in removing dirt deposits and accidental or intended stains and paints. Organic solvents may be used but many of them are well known for their hazards like carcinogenicity for dichloromethane or methyl pyrrolidone. Abrasive cleaning with sand blasting is also hazardous due to the carcinogenic effect of the crystalline silica (quartz) contained the sand. Other abrasive material (metallic grind) used for blasting may also contain hazardous materials. Such blasting procedures are considered too aggressive for many historic restorations. Water jet blasting may be an option but needs high volume water supply and generates wastewater. Dry ice blasting is a safer alternative that is efficient and yet not very invasive for the original material. As the producer presents it, ‘instead of using hard abrasive media to grind on a surface (and damage it), dry ice blasting uses soft dry ice, accelerated at supersonic speeds, and creates mini-explosions on the surface to lift the undesirable item off the underlying substrate’. Dry ice pellets can be made on-site or supplied. A compressed air supply of 80 PSI/50 scfm is needed for frozen carbon dioxide jet. The restoration ofwell-known historic monuments in Prague included facade cleaning with dry ice blasting. Technical experts, architects and historians were pleased with the results and with the working conditions of the restoration teams.

Case/substitution evaluation

Both chemical and traditional abrasive cleaning alters the integrity of the very surface the restorers are trying to preserve. Dry ice blasting is safer and feasible and provides suitable quality to match high requirements of historical restoration. Blasting generates airborne particles detached form the facade's surface that may contain hazardous substances. Adequate respiratory and eye protection is needed. The ice hitting the surface does not melt but it directly sublimates, therefore does not generate waste water. It is a successful substitution of substances that are carcinogenic according to the SUBSPORTplus criteria.

State of implementation

In use

Date and place of implementation

Prague

Availability of Alternative

Alternative available on the market.

Producer/Provider

www.coldjet.com

Type of information supplier

Producer / distributor

Contact

www.coldjet.com

Further information

Case study video: Historic restoration in Prague: click here

Type of publication and availability

presentation, brochure and video freely available on the producer website

Publication source: author, company, institute, year

Case story, presentation and brochure published by Cold Jet LLC on their website.

Publication source

Type of publication and availability

http://www.coldjet.com/en/industries/historical-restoration.php

Date, reviewed

November 26, 2021