Industrial & Consumer Safety

The following are safety guidelines recommended for adhesives and sealants commonly used in industrial and household environments:

Physically Hardening Adhesives: The active components are mainly solid polymers and resins. For application these must be converted to a liquid form. This can either be carried out by users by means of heating (hot melts) or can be carried out by adhesive manufacturers by dissolving the components in organic solvents or dispersing the components in water. The dry, fully-aired adhesive is generally unreactive and biologically inert. There is therefore usually no health hazard. In contrast, there is a potential health hazard from auxiliary components, such as organic solvents, that are present in some of these adhesives. These can make up as much as 80% of the weight of the adhesive product.

  • Hot Melts: These adhesives contain largely polymers and resins and only small amounts of auxiliary materials. There is virtually never a health hazard. When applying these adhesives manually, there is the risk of burns and users must protect themselves against this. During heating, small amounts of auxiliary materials, contaminants and cleavage products can be liberated, but these are insignificant when small amounts of adhesive are being processed. In an industrial or commercial environment, a ventilation system is recommended due to the larger quantities being used and the longer working times with the adhesives.
  • Organic Solvent (e.g. Contact Adhesives): In these adhesives the polymers and resins are dissolved in organic solvents. The hazard potential is determined by the nature of the solvent (e.g. flammability, irritation potential). Due to the high volatility of the solvents, exposure by inhalation of the vapors is the biggest problem. For most solvents the maximum concentration at the work­place and limiting factors are laid down (Workplace limit value, see Glossary). Due to the small amounts of adhesive used by private users, these limit values are generally not reached or are only exceeded for a very short time.
  • Water-Based (e.g. PVA Wood Adhesives): In the adhesives the organic solvents are replaced by water and suitable polymers are dispersed in the water. There are hence no potential health hazards from organic solvents. However, water-based adhes­ives are sensitive to attack by micro-organisms (e.g. mold formation). For that reason dispersion adhesives contain small amounts of preservatives for protection purposes. The potential health hazard is the triggering of allergic skin reactions, for example allergic reactions triggered by natural polymers such as natural rubber and non-modified colophony resins. The risk of sensitization in non-allergic people is generally extremely low due to the very small amounts of preservatives in the adhesives. Skin contact is here the exposure issue. Depending on the mode of application, skin contact may be unavoidable, as for example when using wallpaper pastes. However, here the concentration of preserv­atives is reduced as a result of mixing with water.
  • Plastisols: When applying these adhesives manually, there is the risk of burns and users must protect themselves against this. During heating, small amounts of auxiliary materials, contaminants and cleavage products can be liberated, but these are insignificant when small amounts of adhesive are being processed. In an industrial or commercial environment, a ventilation system is recommended due to the larger quantities being used and the longer working times with the adhesives.

    Chemically Curing: The chemically reactive monomers/oligomers and hardeners and crosslinking agents determine the potential health hazard of these products. Once fully cured, the adhesive polymers are in general non-­hazardous. Exposure and risk considerations hence only apply for the time period up until the adhesives have fully cured. Chemically curing may be classified into Single Component (1-C) and Two-Component (2-C).

Single Component

  • Heat Curing (e.g. epoxies, phenol-formaldehyde): When applying these adhesives manually, there is the risk of burns and users must protect themselves against this. During heating, small amounts of auxiliary materials, contaminants and cleavage products can be liberated, but these are insignificant when small amounts of adhesive are being processed. In an industrial or commercial environment, a ventilation system is recommended due to the larger quantities being used and the longer working times with the adhesives.
  • Moisture Curing (e.g. polyurethanes): This group of adhesives reacts with water from the surroundings or water on the substrate. When applying these materials, it is suggested to wear gloves, and eye protection. These materials cure over a period of hours or even days; however, contact with the skin should be minimized as they can cause some skin irritation/dermatitis. Vapors can cause eye irritation and direct contact to the eyes with rubbing may cause some abrasion to them. In limited use, no additional protection is needed; however, an open area is recommended for production use. As with any moisture curing product, increasing the ambient humidity level will decrease cure time.
  • Cyanoacrylates: This group of adhesives reacts with water from the surroundings or water on the substrate. As private individuals only usually use small drops when applying the adhesive, the potential health hazard here is that if there is contact with the eyes or splashes of adhesive enter the eye then undesired bonding can take place (can gradually be dissolved using a soap solution). When being used industrially and commercially, possible irritation caused by the cyanoacrylate monomer, thermal effects and the rapid polymerization reaction have to be taken into consideration. Increasing the humidity prevents irritation of the respiratory tract. When carrying out major bonding tasks, not only is it recommended to adjust the humidity of the air but also to wear safety glasses and protective gloves.
  • Anaerobic: These types of materials are free radical cure mechanisms and begin to cure when they are confined between substrates of limited dimension, thus removing ambient air. Oxygen stabilizes these products, so the elimination of it (as in a joint), along with the presence of a free radical metallic ion the cure begins. Many of these materials contain some amount of mild acids and acrylic monomers so the use of gloves and eye protection is advised. Generally speaking, these materials are used as threadlocking agents, bearing (cylindrical bonding) retaining, flange sealing and thread sealing. They can be applied via manual application from a packaged bottle, or with automated equipment. Ventilation is not normally needed; however, in flange sealing, larger amounts are applied so open areas are often advised.
  • Radiation Cure: Radiation Cure is a method of initiation of the cure. It utilizes a photoinitiator as one of the raw materials in the adhesive/sealant. Once exposed to the chosen wavelength of energy (ultraviolet, visible, and even microwave) the photonitiator will react and cause the initiation of the curing process. In terms of safety, there are two concerns -- the adhesive/sealant itself, and the energy emitting source. For the adhesive/sealant, there are versions of cyanoacrylate, epoxy, silicone, anaerobic, and acrylic products all available as radiation curing. Thus, refer to the respective product descriptions in this section for handling and exposure limitations. With respect to the energy source, the first topic is microwave energy. While these materials are limited in use, they need to be mentioned, and normal concerns for microwave exposure are valid. These include the very same restrictions as when using microwave ovens at home - microwave energy must always be shielded. Use of ultraviolet light is common and requires the use of eye protection (designed specifically as UV blocking and intensity reduction) as well as skin protection to prevent burns. Many of the radiation curing adhesives utilize high intensity lights which are harmful to look at without eye protection. The same concerns are appropriate when discussing visible light cure. These materials utilize the very same idea of a photoinitiator, but it responds to a different wavelength of light. In this case the concern is the intensity of the light source. Again, use of eye protection is necessary. There are some low intensity visible light curing materials, with corresponding low intensity emitting lamps, but prolonged exposure them is not advised without UV blocking eye protection as some amount of stray UV light is likely to be emitted.
  • Silicones: Single component silicones have very similar handling and use concerns as the single component polyurethanes as described earlier. Therefore, the same handling methodology should be used. This group of adhesives reacts with water from the surroundings or water on the substrate. While both single and two-component materials are available, these comments refer specifically to the single component products. When applying these materials, it is suggested to wear gloves, and eye protection. These materials cure over a period of hours or even days; however, contact with the skin should be minimized as they can cause some skin irritation/dermatitis. Vapors can cause eye irritation and direct contact to the eyes will cause irritation. In limited use, no additional protection is needed, however, an open area is recommended for production use. As with any moisture curing product, increasing the ambient humidity level will decrease cure time.

Two Component

  • Epoxiens : Epoxy materials have both a resin and hardener, which require mixing prior to use. These of these parts should be used with gloves and eye protection as they can cause mild skin and eye irritation. Normally, inhalation is not a concern; however, some people will experience some respiratory tract irritation, so open areas are suggested.
  • Urethanes:When a two-component polyurethane is used, the reaction for curing is the combining of the two parts. The mixed material is similar in safety related concern to the single component urethane as described above.
  • Methyl Methacrylates:This category of adhesives are usually used in structural bonding of metal substrates. Also known as “MMA’s”, these materials have a strong, pungent odor, and can cause headaches, nausea, dizziness and respiratory tract irritation. They cure via the mixing of the two parts, so when handling, gloves and eye protection are recommended. They are irritating to the skin and eyes. Localized ventilation is suggested for prolonged use. Otherwise, application in an open area is suggested.
  • Silicones: Silicones react with water. Depending on the type of silicone, this reaction releases either acetic acid or alcohols. The acetic acid can be clearly sensed by the nose before any irritation begins. In general the slowly released amounts are so small that they pre­sent no health risk, especially in the case of private users. Old formulations of neutral silicones which release butanone oxime must be labeled, but they are only used nowadays for special applications. It should be noted that these products may also be found as single component products.

Pressure Sensitive Adhesives: Private users only come into contact with these adhesives in the form of self-adhesive articles such as labels, adhesive tape, etc. As such these adhes­ives represent no hazard to private users in practice. Such articles are manufactured industrially using adhesives in the form of solutions, but mostly using dispersions and melts.