Chemical Paint Strippers
A 3-Step-Comparison Model for Risk Potentials of Ingredients
Dr. Gerald Altnau
Chemical paint strippers are used to remove old paints & coatings from surfaces and facades, walls and furniture. One differentiates between alkaline and solvent-based paint removers.
In both cases products are applied, which contain chemicals, which need to be so reactive that they attack surface coatings and dissolve them, so that they can be removed mechanically or by water jet.
Before working with chemical paint removers one should be aware, that hygiene standards should be followed and skin contact needs to be avoided with such products, which are designed to attack polymer-based surface coatings, because the risk of skin irritation or corrosion exists or solvents with carrier properties may be resorbed through the skin.
Goggles, correct gloves (for different solvents different glove materials may be needed) and appropriate protective clothing is the first step towards an appropriate personal protection.
After having applied the appropriate protection against skin contact there still exists the often more dangerous and insidious danger of vapours, because solvent-based paint strippers may behave pasty or jellylike in order to stick to vertical surfaces, but depending on the type of solvents used, those may evaporate slowly or extremely fast.
Some solvents can be poisonous, irritate the breathing system, create headache and dizziness or are classified as CMRs (carcinogenic, mutagenic and repro-toxic) and one needs to be protected against inhaling them. This is possible with an appropriate respiratory protection.
Since 6th June 2012 the use of dichloromethane (DCM) - based paint strippers is no longer permitted in the European Union (EU) and one can assume that the number of fatal incidents at workplaces will decline, because DCM is by far the most dangerous paint stripper ingredient as statistics have proven.
When the UK already re-introduces DCM paint strippers under derogations effective December 2014 and Poland seems to ignore the ban, formulators & safety experts in other member states worked on solutions without DCM, aimed at further reducing the risks for users by careful selection of ingredients.
In this phase EASCR observed that paint stripper formulations with highly flammable solvents find increasing use as cost-attractive replacement13). This danger is often underestimated because appropriate skin and breathing protection may not help if a work place catches fire and costly technical measures will be required.
In order to support the development of safer formulations a comparison method is needed to take the right choice.
Painters and decorators are professional users and it is mandatory that they have to follow certain safety regulations at their work places. Therefore one should expect that effective skin protection is generally practiced in their own interest (or requested and supplied by their employers) in form of appropriate Personal Injury Protection PIP (e.g. goggles, gloves and overalls). On the basis that professional users are generally informed about the paint strippers used and work with the recommended glove material, the risk of inhalation or ignition should have a very high priority when comparing risk potentials of different paint stripper ingredients.
A practical comparison model can be built in three steps.
Step 1 - The Vapor Hazard Ratio
The direct comparison of occupational exposure limits (OELs) may lead to a wrong selection, because a concentration value alone does not inform about the type of risk exposed to or how fast an exposure limit is reached or exceeded. Often people have difficulties to realize that a higher exposure limit does not stand for a higher degree of safety at the work place.
The German Technical Rule TRGS 4201) (Process and substance specific criteria for a risk assessment - version of September 1999) offers a good approach, because with the “vapor hazard ratio” (VHR), a comparison of different substances in regard to their exposure limits is possible. This concept is also known in many other countries.
The VHR can also be calculated with the vapor pressure and the mol mass of a substance, which can normally be found in Safety Data Sheets7).
A substance with a low VHR needs less ventilation and with the values of different paint stripper ingredients, different exposure risks can be calculated and compared with. Very high VHR values should catalyze concern that it may be very difficult to achieve sufficient ventilation at all.
Already in 1997 the Technical Committee of the German Federation of the Statutory Accident Insurance Institutions for the Industrial Sector HVBG (Hauptverband der gewerblichen Berufsgenossenschaften) defined different VHR ranges 9).
Today after several years with REACH and new information collected and provided by industry at high cost, long-term inhalation DNELs (Derived no-effect level) seem be a better choice for exposure limits than OELs because they are defined as concentrations at which no effect to the health is expected. These concentration values are part of each REACH registration and may be already available for most of the paint stripper ingredients according to the volumes produced in or imported into the EU.
Interestingly EU Member States still operate with individual national exposure limits for chemicals at the workplace, which sometimes may be higher than the corresponding DNELs and differ from country to country10, 11). Such lists are often limited and may not contain all important paint stripper ingredients.
If one takes a national approach, one has to use the national OELs (e.g. TRGS 900 2) for Germany) for a comparison and fill the data gaps with DNELs as certain national technical rules allow (TRGS 402 3), number 5.3.2. para 3).
EASCR considers all human beings as equal and therefore we favor an approach/comparison based on DNELs (with focus on inhalation) because these values are compared on zero effect levels for workers, which are the same everywhere and dependent on the substance and not on the location of a workplace in a certain country.
VHR Vapor Hazard Ratio = Saturation concentration / DNEL Derived no-effect level
When comparing VHR values one compares the exposure risk but not the complete type of hazard one is exposed to. In above table ten mostly used ingredients of actual paint strippers were compared, as identified by the German Social Accident Insurance for the Construction Industry (BG Bau - GISBAU), with the main ingredients of a DCM paint stripper (dichloromethane & methanol) and three typical flammable solvents.
Because it is a great difference, whether an exposure leads to a reversible irritation (e.g. of the nasal mucous membrane) or to permanent damage (caused by carcinogenic or mutagenic potential) or to an explosion, one needs to go one step further in order to connect the exposure with the hazard of a substance.
A Risk is the chance to be harmed if exposed to a hazard.
A Hazard is any source of potential damage, harm or adverse health effects on something or someone under certain conditions at work 4).
Step 2 - Define the Hazards in an Application
In our proposed approach we define the risk of substances on the base of their health hazard properties by the "Effect Factor Model" and the risk due to their physical-chemical properties by the "Column Model" as described in the Technical Rules for Hazardous Substances (TRGS) 600 from August 2008 published by the German Federal Ministry of Labor and Work5).
For the "Effect Factor Model" there exists the TRGS 600 based on R-phrases, translated into H-phrases by Dr. Birgit Stöffler7)
The “Column Model” from the IFA (Institute for Safety at Work of the German Statutory Accident Insurance) is based on H-Phrases from the CLP Regulation 6) and offers risk factor ranges for formulations, as visualized by Stöffler7). In a simplified approach we worked with the lower limit of the highest category for physical-chemical and environmental properties and with the mean value for the others.
In Table 2 we combined H-phrases and Effect Factors from both models in order to assess hazards which can play a role when stripping paints.
In Table 3 we sorted H-phrases and hazard pictograms by the four Categories of the new GHS classification and translated them into the corresponding Effect Factors (EF).
Interestingly this perspective shows that the risk increases from category 4 to 1 within an individual hazard class (e.g. corrosion or Acute Toxicity), but the number of category is not a good measure for the hazard potential in correlation to the severity of the effect.
Category 1 for example contains H-Phrases with Effect Factors in the range from 5 to 50.000 depending on the type of hazard.
So a pictogram or a category is not an “easy guide” to compare and select safer substances.
In general one could argue that a painter or decorator with the correct appropriate protection may be relatively safe against inhalation hazards and skin contact, so that corresponding Effect Factors may not be taken by their full value, but for our comparison we disregarded this point of view, because we have learned that this industry tends to underestimate the danger and experts have found out that there exists wide lack of information about official regulations8).
The Hazard Value HV of a substance (paint stripper ingredient) can now be defined as sum of its Effect Factors translated from its H-phrases.
HV substance 1 = EF1 + EF2 + EFn
Step 3 - Combine the Exposure with the Hazards in an Application
Finally the Paint Stripping Risk Value RV of a substance is calculated by adding the vapor hazard ratio VHR to the hazard value HV, what is now the combination of exposure and substance specific hazards to define a risk:
RV subst 1 = VHR subst 1 + HV healthsubst 1 + HV phys.-chemsubst 1 + HV environm.subst 1
The following Table 4 shows the calculated Risk Values of the main ingredients in German paint stripper formulations used as alternatives to DCM:
The higher the value, the higher the risk for the user!
In order to allow a comparison DCM and methanol (main ingredients of DCM paint strippers) as well as NMP have been included. So on one side it allows to recognize the step change towards safer paint stripping without DCM paint strippers and on the other side it visualizes, which risk is introduced by flammable solvents.
Table 5 concentrates the information and identifies the main drivers of a Risk Value of a paint stripper ingredient. It is interesting that in most of the cases it is the VHR in combination with a health or a phys-chem. hazard. Environmental hazards don't play a role among the exemplary substance group.
Summary & Conclusion
By combining 20 year old concepts from official regulations like vapor hazard ratio VHR and effect factor & column model in a new straight forward 3-step-approach, it is possible to compare risk potentials of ingredients of paint stripper formulations by their risk values RV: The higher the RV the higher the hazard potential.
For substances with a VHR > 1.000, exceeding the exposure limit can only be avoided with optimal safety precaution.
The grouping of health-, physical-chemical and environmental hazards allows to identify main drivers, or combinations, so that formulators and users can decide how to deal with issues or choose alternatives.
The risk values of flammable solvents should raise concern, because those found increasingly use after the DCM ban and the risk may be undervalued.
It should not be forgotten, that besides the paint stripper used, also the ingredients of the coatings to be removed may have an influence on the personal injury protection to be chosen.
This approach is not limited to paint strippers.
1. TRGS 420 „ Verfahrens- und stoffspezifische Kriterien (VSK) für die Gefährdungsbeurteilung, September 1999 - http://www.baua.de/de/Themen-von-A-Z/Gefahrstoffe/TRGS/TRGS-420.html
2. TRGS 900 Occupational Exposure limits – amended 13 Sept 2012 - http://www.baua.de/de/Themen-von-A-Z/Gefahrstoffe/TRGS/TRGS-900.html__nnn=true
TRGS 402 “Identification and assessment of the
risks from activities involving hazardous substances: inhalation exposure,
4. CCOHS on Hazard and Risk - http://www.ccohs.ca/oshanswers/hsprograms/hazard_risk.html
5. TRGS 600 - Technical Rules for Hazardous Substances, August 2008 - http://www.baua.de/en/Topics-from-A-to-Z/Hazardous-Substances/TRGS/TRGS-600.html
6. IFA Institut für Arbeitsschutz der deutschen Gesetzlichen Unfallversicherung - Column Model – August 2014 - http://www.dguv.de/ifa/Praxishilfen/Hazardous-substances/GHS-Spaltenmodell-zur-Substitutionspr%C3%BCfung/index.jsp
7. Dr. Birgit Stöffler - Substitution von Gefahrstoffen – ECOMED Verlag 2014 - http://www.ecomed-storck.de/Gefahrstoffe/Praxishilfen/Substitution-von-Gefahrstoffen-Softcover.html
8. RPA Report for the EU Commission April 2007, Impact Assessment of Potential Restrictions on the Marketing and Use of Dichloromethane in Paint Strippers - http://ec.europa.eu/enterprise/sectors/chemicals/files/markrestr/j549_dcm_final_report_en.pdf
9. BGI 536 Gefahrstoffe Gefährliche Chemische Stoffe Merkblatt M 051 - Hauptverband der gewerblichen Berufsgenossenschaften - Februar 1997 - http://timiela.de/Arb/PDF_Referenzen%20und%20Anwendbare%20Dokumente/bgi536_MerkblattGefStoffe.pdf
10. German Research Foundation (DFG) - Permanent Senate Commission - Derivation of exposure limits (MAK-value) - http://www.dfg.de/en/dfg_profile/statutory_bodies/senate/health_hazards/structure/working_groups/derivation_mak/index.html
11. Dr. Gerald Altnau - Bewertung des Risikopotenzials von Lösemitteln - Farbe & Lack 105. Jahrgang 1/99 Seite 38 https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0ahUKEwiTtYmE8pTKAhVEXhQKHW7mDSAQFggoMAE&url=http%3A%2F%2Fwww.european-coatings.com%2Fcontent%2Fdownload%2F80928%2F1098709%2Fversion%2F1%2Ffile%2F28001.pdf&usg=AFQjCNF7pAnpgORlbdXMK7JO_Bg6lVFMxg&cad=rja
12. Dr. Gerald Altnau - Safer solvents for safer products - European Coatings Journal 09/2001, page 39 https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd=4&cad=rja&uact=8&ved=0ahUKEwjtyIfc8pTKAhVBaRQKHeNQAHoQFgg3MAM&url=http%3A%2F%2Fwww.european-coatings.com%2Fcontent%2Fdownload%2F64128%2F762647%2Fversion%2F1%2Ffile%2F33265.pdf&usg=AFQjCNE8n9nmfV_TObuiG8g1flZAZzNHbQ
13. EASCR press release March 2011 http://www.eascr.com/documents/2011.03%20EASCR%20PR%20zur%20ECS%20-%20engl2.pdf