Methyl Ethyl Ketoxime (MEKO): Applications, Products, and Safety Measures
In the world of chemicals, Methyl Ethyl Ketoxime (MEKO) is a versatile compound known for its unique properties and applications. This blog aims to explore MEKO, its uses across various industries, and the essential health and safety considerations associated with its handling, and why it should be avoided.
What is Methyl Ethyl Ketoxime (MEKO)?
Methyl Ethyl Ketoxime, commonly referred to as MEKO, is a chemical compound with the molecular formula C5H11NO. It is categorised as an oxime Crosslinker for silicones and is characterised by its distinctive odour. MEKO is a colourless to pale yellow liquid that is soluble in water and commonly used for its reactivity with compounds containing isocyanate groups. It has several valuable applications across different industries.
Why is MEKO Used?
MEKO is utilised in a variety of applications due to its unique properties, including:
- Anti-Skinning Agent: MEKO is often used as an anti-skinning agent in coatings and paints. It prevents the formation of a skin or surface film when the product is exposed to air, thus extending the shelf life of these materials.
Crosslinking Agent: In the production of adhesives and sealants, MEKO acts as a crosslinking agent. It helps improve the durability and performance of these products.
- Inhibitor: MEKO is employed as an inhibitor in industrial processes involving isocyanate compounds, such as the production of polyurethane foams. It stabilizes these compounds, preventing premature reactions.
- Curing Agent: Some silicone sealants use MEKO as a curing agent, aiding in the hardening and setting of the sealant.
Products That Use MEKO
MEKO is incorporated into a range of products across different industries. Some of the common products that may contain MEKO include:
- Paints and Coatings: MEKO is added to paints and coatings as an anti-skinning agent, ensuring the product remains usable over time.
- Adhesives and Sealants: MEKO is used as a crosslinking agent in adhesives and sealants, enhancing their performance and durability.
- Polyurethane Foams: In the production of polyurethane foams, MEKO serves as an inhibitor to prevent premature reactions during processing.
- Silicone Sealants: Certain silicone sealants use MEKO as a curing agent to facilitate the hardening process.
Zero or No Meko Silicone is the new-generation MEKO-free oxime. It is odourless, safer for users and environmentally friendly. Its curing speed, adhesion, mechanical properties and more are comparable to those of conventional MEKO silicones. All of AC Cable Solutions duct Sealing products, DuctSeal LG, DuctSeal HG, DuctSeal FR & GreyStuff contain zero MEKO.
Why should MEKO be avoided?
Oxime silicones based on methyl ethyl ketoxime are considered to be carcinogenic. Protective gloves and masks are required, as well as sufficient ventilation. In some countries, silicones based on MEKO have been outlawed. (Most of Europe)
Europe has classified any product containing MEKO to be designated a hazardous substance in Europe (Legal Reference 1, 2, 3)
In March 2022, the European Union classified MEKO as a Carcinogen Category 1B. This classification, per the European Commission: ATP 15-part 3 Annex VI, requires formulations with 0.1% or more MEKO content to include carcinogen GHS labelling.
If you are using sealants for duct sealing, general gap filling, or linear gaps, then please consider a zero MEKO product. To view our Zero MEKO cable & pipe sealing systems, click here.
The effects of MEKO
The short-term risks of MEKO exposure when using oxime silicone sealants are associated with acute toxicity upon contact with the skin, eyes, or inhalation [1, 2]. At low concentrations resulting from oxime curing, skin contact may lead to mild skin irritation or trigger allergic dermal reactions. Eye contact is particularly severe, causing serious eye irritation upon exposure to fumes and irreversible eye damage upon concentrated contact . Although acute toxicity through inhalation is classified as low, it may still result in respiratory irritation, posing significant long-term exposure risks. Acute oral toxicity is low but is less relevant for sealant applications.
Even more concerning is the carcinogenicity of MEKO over an extended period of exposure. MEKO is categorised as a Class 3 carcinogen by Safe Work Australia [1, 2]. Substances with this classification typically bear a 'suspected of causing cancer' warning as per Australian Work Health and Safety (WHS) legislation. In a carcinogenicity study, rats were exposed to doses of 374 ppm through inhalation for 18 months . At the conclusion of the study, researchers observed degeneration of the respiratory system and a significantly increased incidence of hepatocellular carcinomas, the most common type of liver tumour . These findings, in conjunction with other MEKO studies, strongly indicate the carcinogenic nature and long-term exposure risks associated with MEKO.
It is important to comprehend the risks associated with the use of wet silicone sealants in order to minimise and effectively control them. The American Industrial Hygiene Association recommends a maximum MEKO exposure limit of 36 mg/m3 (10ppm) . To maintain MEKO concentrations below this level, workspaces should be adequately ventilated, and all other personal protective equipment recommended by the sealant manufacturer should be worn when using oxime-based sealants safely. Although there are other neutral curing silicones under development with lower carcinogenic risks, such as alkoxy and amine curing sealants, each still produces by-products that can be harmful to human health. Inherently, the use of any wet sealant presents some degree of risk to human health and safety..
While exposure limits and personal protective equipment do offer a foundational level of risk reduction, those well-versed in the Hierarchy of Hazard Controls recognize that elimination and substitution are more preferable and potent means of risk reduction. Decreasing the amount of wet sealant used can significantly diminish workplace risk by reducing the emission of toxic by-products into the environment. A viable alternative to wet silicone seals, when required to seal cable ducts, is to use our mechanical transit seals from Kraso GMBH. Click to view our range.
Classification of OXIME-based sealants according to ECHA Europa
Name: 2-Butanone Oxime (MEKO)
Type of classification: harmonised classification
Classification according to the harmonized classification and labelling (ATP15) as stated in Annex VI of Regulation (EC) 1272/2008 approved by the European Union and self-classification.
H301: Toxic if swallowed.
H312: Harmful in contact with skin.
H336: May cause drowsiness or dizziness.
H370: Causes damage to organs <or state all organs affected, if known> <state route of exposure if it is conclusively proven that no other routes of exposure cause the hazard>.
H315: Causes skin irritation.
H318: Causes serious eye damage.
H317: May cause an allergic skin reaction.
H350: May cause cancer <state route of exposure if it is conclusively proven that no other routes of exposure cause the hazard>.
H373: May cause damage to organs <or state all organs affected, if known> through prolonged or repeated exposure <state route of exposure if it is conclusively proven that no other routes of exposure cause the hazard>.
GHS06: skull and crossbones
GHS08: health hazard
The choice to opt for products containing MEKO is a matter entirely under your control. However, the purpose of this blog is to shed light on the potential risks associated with MEKO. It is worth noting that Europe has classified MEKO as a Carcinogen Category 1B, and it's likely only a matter of time before the UK follows suit.
At AC Cable Solutions, our recent focus has been on the development of duct sealing systems designed to effectively seal cables and pipes within ducted networks. Right from the outset, our primary goal was to create a silicone sealant that completely eliminates the use of Methyl Ethyl Ketoxime (MEKO).
Benefits of a zero MEKO Silicone:
- Far less hazardous for the user
- Less odour & fumes – better for confined spaces
- No requirements for a face mask
- Less labelling requirements
- Significantly easier for cosh assessments
- Freely able to sell & use in all countries.
ECHA Europa. https://echa.europa.eu/registration-dossier/-/registered-dossier/14908/2/1
Safe Work Australia. Hazardous Substances Information System (HSIS). [cited 16 April 2018]; Available from: http://hsis.safeworkaustralia.gov.au/HazardousSubstance.
National Industrial Chemicals Notification and Assessment Scheme. HUMAN HEALTH TIER II ASSESSMENT FOR 2-Butanone, oxime CAS Number: 96-29-7. [cited 16 April 2018]; Available from: https://www.nicnas.gov.au/chemical-information/imap-assessments/imap-assessment-details?assessment_id=103#cas-A_96-29-7.
REACH Dossier. Butanone Oxime (96-29-7). [cited 16 April 2018]; Available from: http://echa.europa.eu/web/guest/information-on-chemicals/registered-substances.
Written by Carl Pike - The Duct Sealing Man