Portable Sanitation Association International

Association Insight Dec 01 2021

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4 I PSAI Association Insight, December 1, 2021 Winterization: How to Prepare Restrooms and Equipment for Extremely Cold Weather (Part 2) (continued from page 2) dilution than magnesium chloride. In practical terms, that means that two parts of CaCl 2 does more work in less time than three parts of MgCl 2 . That article also suggests that magnesium chloride is more corrosive to concrete, more toxic to plant life, and more damaging to metals than both calcium chloride and common salt. Methanol Another additive commonly used in extremely cold conditions is methanol, also known as methyl alcohol or methyl hydrate. Methanol is the simplest alcohol with the formula CH 3 0H, often abbreviated to MeOH. It is a light, volatile, colourless, and flammable liquid with a distinct alcoholic odour similar to that of ethanol (the main alcohol used in spirits like vodka and gin). Methanol is reasonably abundant, with more than 20 million tons produced annually and largely distributed by a number of petrochemical suppliers. Prices will vary, but current prices for bulk methanol in the US are just under $3 a gallon. When it's used to prevent freezing, 6.4 fluid ounces of methanol per gallon (50ml per litre) of water will protect tanks at 28°F (-2°C). At higher concentrations, methanol will prevent freezing at even lower temperatures. A concentration of 30 percent methanol to water (38 fl oz per gallon or 300ml per litre) will protect against freezing down to -4°F (-20°C) without being corrosive to aluminium or steel. The freezing point of different concentrations of methanol solution are shown in Table 2. contaminate the freshwater tank on the truck. That's useful because you can't wash down with salt brine; it leaves a chalky residue when it dries. Using a separate container is a low-tech option that doesn't require any extra plumbing on the truck. It allows you to fill buckets by gravity, just using a hose, and means you can remove the tank from the truck when the weather improves. If you do use salt, you need to keep in mind that salt brine is corrosive. It will rust steel, and it will react with aluminum to produce a white oxide and surface pitting. This corrosion will eventually weaken any fixtures and fittings. Rinsing the pump, hoses, and waste tank every day will help to reduce the damage. A strong cleaner such as Scale-X should also help to remove any residue. Operators buying new tanks should consider getting the inside painted with a protective coating before use. Although salt brine works well, it's not effective when temperatures drop below 25°F (-3°C). When that happens, operators will need to find an alternative approach. Two alternatives with a slightly lower freezing point than salt brine are magnesium chloride (MgCl 2 ) and calcium chloride (Ca Cl 2 ). Both can be bought as crystals or flakes or in a solution up to 30 percent. These are commonly used as additives in antifreeze and deicers and can be mixed in the same way as salt brine. Many academics have compared the properties of sodium, magnesium chloride, and calcium chloride when used as frost protectants. One article published by Peter Chemicals 1 states that calcium chloride is the less corrosive and works in greater (continued on page 5) CONCENTRATION OF SOLUTION METHANOL DOSE (PER GAL) METHANOL DOSE (ML PER LITRE) FREEZING POINT OF SOLUTION 5% 6.4fl oz 50ml 28°F (-2°C) 10% 12.8fl oz 100ml 22°F (-°5C) 15% 19.2fl oz 150ml 17°F (-8°C) 20% 25.6fl oz 200ml 11°F (-11°C) 25% 32.0fl oz 250ml 4°F (-15°C) 30% 38.4fl oz 300ml -4°F (-20°C) Table 2. Mixing Guide: Methanol Solution NOTE 1: Contact with bare skin at very cold temperatures can lead to serious injury and harm. Correct PPE must be worn when handling these solutions. NOTE 2: Methanol can be flammable when mixed with water. Do NOT exceed a methanol:water concentration greater than 33 percent.

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