Especially on construction sites and outdoors, you sometimes stand in the rain. To avoid getting into the fire and standing completely soaked in your workwear, waterproof or water-repellent protective clothing is the right choice. The protection professionals explain what the difference between waterproof and water-repellent is and what the water column is all about.
There is no such thing as bad working weather, there is the right protective clothing!
The water column determines the criteria according to which the water permeability of a substance or membrane is measured. Or to put it more clearly: How quickly does a fabric or membrane allow water to pass through?
Difference waterproof & water-repellent
Waterproof means that the material for the workwear is so dense that no water can pass through. in this case, you should stay dry, no matter how long you are out in the rain. If a work jacket is really waterproof, often only the surface soaks up. The clothing inside remains dry and protected by the special waterproof membranes. If the workwear is water-repellent (waterproof), the water will roll off the surface and be prevented from penetrating inside. In this case, in the event of continuous or heavy rain, it cannot be ruled out that it will also get wet inside the workwear over time.
The water column as a unit of measurement
The water column is the unit of measurement with which much water pressure can be applied to a fabric before it is considered to leak. It is the guideline value for the waterproofness of the fabric and serves as a reference value for rainwear and outdoor use, for example. The water column is measured and included in the product properties. This makes it easier to choose which clothing is suitable for the respective application and offers the necessary protection.
The higher the water column, the more waterproof the fabric is.
How does the water column test work?
In principle, the water column is always tested in a similar way. In a hydrostatic water pressure test, the outside of a substance is tested in the laboratory. In this process, a piece of fabric is clamped in a frame and exposed to increasing water pressure. As soon as three drops visibly penetrate the material, the test is over and the water column is determined.
Then it is recorded how long it took the water to make its way through the fabric. The pressure that was at work at this point in time is then given in millimeters of water column.
The standardised measurement
The measurements of the water column are carried out according to different norms and standards. For example, an international ISO 811 (DIN EN ISO 811:2018-08) or the AATCC standard 127 from the USA. In Germany, the European standard DIN EN 343:2010-05 (protective clothing against rain) comes into force for clothing.
If a textile is marked with 10,000 mm WS, the textile has a water column of 10,000 millimeters. 1,000 millimeters of water column corresponds approximately to the pressure of 0.1 bar.
For comparison:
1,000 mm: This is the pressure exerted by a reclining person weighing 80 kg at a height of 1.80 m. When sitting, a person weighing 80 kg generates a pressure of 5,000 mm due to the smaller area. In kneeling, it is already 14,000 mm at 80 kg.
Note: This is also the reason why you should not touch the tarpaulins in the tent when it rains. What previously kept the rain off leaks due to the higher pressure and results in a happy drop on the sleeping bag
How waterproof the rainwear must be is determined by the amount of pressure generated during the work activity. The more pressure is generated, the higher the water column of the textile must be. Therefore, seek advice from an occupational health and safety specialist so that the right protective clothing is used.