In machining enterprises, machine tool operators and other workshop personnel face a high risk of inhaling airborne droplets and various odorous gases containing working media. In most situations, these consist of putrid odors caused by fluid spoilage, followed by the inherent chemical scents of the working media’s components. These emissions directly trigger strong olfactory sensations.
1. Understanding the Mechanics of MWF Odors
The so-called sense of smell is the biological perception of odors. When a portion of organic or inorganic compound molecules floating in the atmosphere is inhaled through the nostrils, they are captured by the olfactory cells at the uppermost part of the nasal cavity.
Once captured, those cells become excited. The chemical information carried by the molecules is converted into electrical signals and sent to the brain. As soon as the olfactory threshold is reached, the sensation of smell is produced.
It is important to note that metabolites generated by microbial contamination often produce the most intense foul odors. Among these, Hydrogen Sulfide (H2S) is the most representative and problematic.
2. The “Monday Morning Phenomenon” in Machining
The human olfactory threshold for H2S is extremely low—between 0.012 and 0.030 mg/m³—making it incredibly easy to detect.
When a workshop shuts down on Friday and the working fluid is left stagnant over the weekend, anaerobic bacteria and other microorganisms multiply rapidly, excreting large amounts of H2S. Due to the coverage of the tramp oil slick and the stagnation of the liquid, the H2S temporarily accumulates beneath the surface.
However, when the machine is turned on and the liquid is agitated, this gas is abruptly released. This results in a concentrated putrid smell spreading throughout the workshop when work resumes on Monday morning. This widespread issue is known as the “Monday Morning Phenomenon.”
Besides hydrogen sulfide, this rancid odor also includes compounds such as lower amines, thiols, and lower acids. These foul odors have a severe detrimental effect on the operating environment (especially in closed, constant-temperature workshops) and lead to significant user complaints.
3. Sources of Malodorous Substances in Metalworking Fluids
Water-based metalworking fluids emit a variety of malodorous substances. As shown in Table 1 below, microbial contamination is the primary source of these odorous pollutants.
Table 1: Sources and Characteristics of Malodorous Substances in MWF
| Substance Name | Primary Source | Nature of Odor |
|---|---|---|
| Hydrogen Sulfide | Microbial metabolites; residual impurities of sulfur-containing additives | Rotten egg odor |
| Ammonia | Microbial metabolites; components contained in the product | Urine odor, pungent odor |
| Amines | Microbial metabolites; components contained in the product | Fecal odor |
| Hydrocarbons | Components contained in the product | Pungent odor |
| Aldehydes | Microbial metabolites; components contained in the product | Pungent odor |
| Fatty Acids | Microbial metabolites; components contained in the product | Pungent odor |
| Alcohols | Microbial metabolites; components contained in the product | Pungent odor |
| Phenols | Components contained in the product | Pungent odor |
| Esters | Components contained in the product | Perfume odor, pungent odor |
4. The 6 Major Health Hazards of MWF Odors
Malodorous gases produced through pathways like bacterial spoilage pose numerous hazards to the human body’s systems:
① Hazards to the Nervous System: Long-term stimulation by low-concentration malodorous substances first causes olfactory fatigue, leading to a loss of smell. This subsequently disrupts the regulatory functions of the excitation and inhibition processes in the cerebral cortex. The common hydrogen sulfide gas not only smells foul but also exerts toxic side effects on the nervous system.
② Hazards to the Respiratory System: When operators open equipment doors or enter confined spaces of large working fluid sumps, the accumulation of massive malodorous gases can cause a reflexive, complete cessation of breathing. This severely hinders normal respiratory functions. A sudden exposure to high-concentration malodorous substances can also cause pulmonary edema, which can be life-threatening in severe cases.
③ Hazards to the Circulatory System: Along with changes in the respiratory system, variations in pulse and blood pressure will occur. For instance, if H2S gas enters the bloodstream through the respiratory tract, it interacts with cells to produce toxicity. This hinders oxygen transport in the body, causing tissue hypoxia.
④ Hazards to the Digestive System: Working long-term in an area with spoiled working fluids forces frequent exposure to malodors. This can induce symptoms such as anorexia, nausea, and vomiting. This loss of appetite can further develop into a decline in overall digestive functions.
⑤ Hazards to the Endocrine System: Frequent and prolonged stimulation by malodorous substances can cause endocrine dysfunction, negatively affecting the body’s metabolic functions.
⑥ Other Health & Safety Hazards: The continuous impact of malodorous substances can make operators irritable, depressed, and suffer from insomnia. It leads to a lack of concentration and memory loss, which inevitably reduces work efficiency and may even trigger serious workplace accidents.
Conclusion
Therefore, figuring out how to reduce the inherent component odors and rancid putrid odors of metalworking fluid products is a critical topic for R&D engineers. It is a vital issue directly related to environmental safety and employee welfare in the manufacturing industry.
