SILO GAS The Canada Plan Service prepares detailed plans showing how to construct modern farm buildings, livestock housing systems, storages and equipment for Canadian Agriculture. This leaflet gives the details for a farm building component or piece of farmstead xquipment. To obtain another copy of this leaflet, contact your local provincial agricultural engineer or extension advisor. SILO GAS At the corner's inquest, the forensic scientist reported that the victims' lungs showed massive bleeding and contained high levels of methemoglobin, evidence of exposure to a strong PLAN M -7410 REVISED 88:06 oxidizing agent. This was attributed to nitrogen dioxide (N02), or silo gas. FOREWORD Another more recent case emphasizes that N02 is not the only In 1977, near Gananoque, Ontario, the Conners were gas hazard in farm silos. In 1987, Wayne Smith, a farm employee of Dwight Gilmer and Sons, South Mountain, harvesting their corn crop somewhat early because of planned highway construction nearby. On Monday, September 12, they Ontario, entered a tower silo. It had been lined with a continued filling the silo but stopped on Tuesday because of suspended plastic bag, converting the silo to an oxygen-limiting storage for high moisture shelled corn. Smith rain. was working between the concrete wall and the slack plastic liner above the corn, tramping down some corn that remained On Wednesday, September 14, they decided to resume around the inside perimeter of the bag after the last of the free- harvesting. The silage distributor had not been adjusted and flowing corn had been augered out. silage had piled about 5 m higher against the silo wall at the chute side. From there it sloped steeply downwards towards Apparently the liner ripped open at one of the seams, perhaps the opposite side. Edward Conner (a son) apparently decided spilling C0 2 gas into the space where Smith was working. His to level the silage and adjust the distributor before restarting body was found some time later, where he had tumbled filling operations. Because all the chute doors were closed through the ripped liner and into the gas -filled space inside. except the top one, he decided instead to go in through the roof opening. Using a 7 m rope ladder, he let himself down the 9 m drop. These tragic events remind farmers and silo service people of the deadly nature of the gases sometimes found in and around farm silos. This publication explains the silo gas problem and Jack Conner (the father) returned from town at about 11:00 gives some safety rules for preventing further accidents of this a.m. and noticed that Edward was missing. A hired man, kind. William Carr, climbed the outside silo ladder, looked in, shouted that something was wrong, then jumped in. He landed part way up the silage slope. RECOMMENDED PROCEDURES - A SUMMARY 1. POST A WARNING SIGN in an obvious place such as on Hearing Carr's shout, Jack Conner climbed the outside ladder; the feed room door or beside the silo chute. Many silo he saw Edward lying at the bottom of the slope and William builders provide such signs, some with operating lying part way up. Mr. Conner yelled out that the boys were in instructions warning of gas and injury hazards peculiar to trouble. Another brother, Eldon Conner, ran from the house their own brand of silo. The message can be quite simple, and up the silo chute, followed by another hired man, Don such as DANGER, SILO GAS. Littlejones. Eldon kicked in two silo doors and entered. He tried without success to move Carr, then went farther down the 2. Check to see if your LOCAL FIRE DEPARTMENT (or slope to help his brother, Edward, and collapsed beside him. similar emergency service) has the pressure demand The father watched all of this from the top of the outside ladder! breathing apparatus with a long air-hose for such emergencies. Diving gear (SCUBA) is not suitable because the back-pack air tank is too big to be worn while Don Littlejones tried twice to pull Carr up to the silo chute. Jack climbing the silo chute or the outside ladder-cage. went back down the outside ladder, started up the tractor and 3. VENTILATE THE FEED ROOM in case silo gas spills out forage blower to ventilate the silo, then went up the chute. of the silo doors or is blown out by the silo unloader. Firemen and ambulance (called by Mrs. Conner) arrived on the scene. 4. During silo filling operations DON'T GO INTO THE SILO just to level the silage; instead, make adjustments to the Then the tractor running the blower ran out of fuel. Littlejones silage distributor at the top of the silo to keep the silage changed tractors, but broke a shear-pin when restarting the leveled during filling. blower. This had to be replaced before silo ventilation could be 5. It is sometimes necessary to go into a silo after filling continued. The am bulance attendant tried to climb he silot (such as to level and tramp the silage, install a plastic chute with an air-pack, but it was too big for the chute and had cover sheet, or to setup the silo unloader). DO THIS AS to be dropped. Without the air-pack, his rescue attempts were SOON AS THE LAST LOAD IS PUT IN, AND LEAVE THE futile. BLOWER RUNNING while inside. Don't wait until the next day. When opening a chute door into the silo, climb farther The bodies of the three men were finally removed with an up the chute (not down), in case silo gas spills out of the aerial platform, from which were suspended two ladders lashed doorway. together and lowered through the roof door to reach the silage surface. 6. Previous bulletins have recommended a safety harness The acid content of the silage continues to increase over a (or at least a loop of rope under the armpits) with a rope period of several weeks (depending on the chemistry of the leading to a helper at the top (the 'buddy system'). This silage material and the air tightness of the silo). Eventually, the was not a bad idea, but if you fall, ONE PERSON ALONE increasing acidity kills off the acid-forming bacteria that COULD NEVER PULL YOU UP THE SILO WALL and out produced it and inhibits the growth of molds and fungus that through the roof hatch or silo chute doors to safety. Two could further damage the silage as feed. This is the normal helpers is the minimum! silage making process which takes place in a silo with reason- ably airtight walls. ONE SILAGE GAS (C02) IS ALWAYS 7. Before entering a previously-filled silo, check the depth of PRODUCED in this process. The period of most rapid gas the settled silage. To make sure that the air-blast is production is during the first 6-7 days after filling. During this reaching all the way down into the headspace, attach a period the total volume of the various gases represents several tube adaptor to the blower pipe (see Figures 4 and 5). times the volume of the silo! For the next 3-4 weeks the gas Leave the chute doors closed and VENTILATE THE SILO production tapers off. Some gases stay trapped within the by running the forage blower. Larger silos and deeper silage during the storage period and silage settlement headspaces require more ventilation time (see Table 1). continues to squeeze the gases into the headspace above KEEP THE BLOWER RUNNING while you are in the silo. (see Figure 1). 8. Once operating, the silo unloader can ventilate the silo quite effectively. However, if the silo unloader fails and Another family of gases, the OXIDES OF NITROGEN (NOX), requires service in a recently filled silo, one must assume can also be produced. Any weather condition, cultural practice that some gas may have accumulated. In this case, or silage additive that increases the dissolved nitrate (N03) reventilate with the forage blower- and drop-pipe as in content of the plant material also raises the risk of producing recommendation 7, above. this group of deadly gases. The period of greatest danger is up to 3 weeks after filling. 9. If you discover someone collapsed in the silo, the first and most important step is to start the forage blower and VENTILATE THE SILO. Providing a fresh air supply is the For example, a drought period during the corn growing season most positive and immediate help to both victim and can cause a buildup of nitrate in the soil and the corn plants. The corn is then harvested before the thirsty plants can rescuers. convert the nitrate into useful food proteins, and the unwanted 10. As soon as the victim is outside in the fresh air, APPLY nitrogen is released as nitrous oxide (N20) and nitric oxide ARTIFICIAL RESUSCITATION, if necessary, to restore (NO). The N20 is produced in only minor quantities and is breathing. Obtain medical assistance. relatively harmless (laughing gas, an anaesthetic), but the NO is another matter. This unstable NO gas can be produced in 11. Chemical gas detectors presently available are accurate considerable quantities and it quickly combines with any enough but they are not suitable for operators who do not oxygen remaining in the silo headspace, forming deadling N02 also have the remote air supply equipment for silo entry. gas. Tests for C02 and NOx, should be carried out using two tubes for each gas. Take samples just above the lowest point of the silage surface. Other factors that can increase the nitrate content of silage are nitrogen fertilizer overdose (including manure), black soils that 12. Oxygen-limiting silos are a special case. If you have to are high in organic matter, and silage additives containing enter one of these silos for any reason, you must wear an nitrate nitrogen (for increasing the protein equaivalent of cattle external air supply. This consists of a pressure tank, a feed). For example, the Conners, prior to their accident, had supply hose long enough to reach into the silo, a been pumping ammonium nitrate solution through the forage 'pressure-demand' type of supply regulator and a full-face blower while filling the silo. Urea is another nitrogen chemical mask. sometimes used this way. MAKING SILAGE SILO GAS PROPERTIES Fresh silage material (corn, grains, grasses or legumes), when chopped and blown into silos, is living plant material. During CARBON DIOXIDE (C02) is not itself damaging to health. Its the ensiling process this living material quickly uses up the danger lies in the factthat in silos and similar tight spaces it limited supply of atmospheric: oxygen entrapped within the replaces the oxygen of the air (normal air is about 21% compressed silage mass, and dies. In this respiration process oxygen, 79% nitrogen and 0.03% carbon dioxide). In the oxygen is converted into some water and carbon dioxide oxygen-limiting silos, the contained atmosphere will be almost (C02). At the same time, acid-forming anaerobic microbes entirely C02 and nitrogen (N2); human survival in this multiply rapidly in the warm moist silage. They feed on part of atmosphere depends entirely on a safe, external air supply. the sugars and starches in the silage material and convert Carbon dioxide is an odorless, tasteless, colorless gas that is them to organic acids (lactic, acetic, etc.). These acid-forming 53% heavier than air. Humans and animals fortunately have a bacteria also produce more C02. built-in warning system for C02; when it reaches a certain concentration in the bloodstream, it triggers a nervous impulse and the victim gasps for air. At higher concentrations this reflex or 58% heavier), so it too accumulates at low points in the silo action is inhibited and the victim is asphyxiated. The C02 headspace, feed room, feed alleys, etc. The threshold limit 'threshold limit value' (TLV-STEL, explained later) is 15 000 value (TLV-STEL) is set at only 5 ppm. At this level it is barely ppm (parts per million), or 1.5% by volume. detectable by smell. When produced in sufficient quantities it is so dangerous that it can be a threat to man and beast by In conventional top-unloading silos with roofs, C02 can spilling over into the silo chute and draining down into the feed accumulate to dangerous concentrations when trapped at low room and connecting stable. points near the silage surface, and this risk should not be disregarded (see Figures 1 and 2). Nitrogen dioxide is deadly because when inhaled it dissolves with moisture on the wetted internal surfaces of the lungs, NITROGEN DIOXIDE (N02) is a deadly gas, appearing as a instantly forming potent nitric acid (4N02 + 2H20 + 02 -> 4HN03). reddish to yellowish-brown haze, with an acrid or bleach-like Here it 'burns' the sensitive oxygen-transfer surfaces of the odor. Like C0 2, it is heavier than air (its relative density is 1.58, lungs, effectively stopping any further oxygen supply to the 1 silo chute doors, closed for filling 1 wind blows through open roof hatch and top 2 top of silage just after filling of chute, ventilates silo dome and top of 3 settled silage headspace 4 dense silo gas, squeezed out of the silage, 2 highest concentration of silo gas is at the remains in the headspace lowest part of the headspace 3 workman opens chute door, silo gas pours down into chute Figure 1 Typical unsealed tower silo just after filling Figure 2 Behavior of silo gas on opening of a silo chute door body. Tiny blood vessels in the lungs break down, causing Another of these pumps, made by Drager in Germany (Figure massive bleeding, and death results (When Eldon Conner went 3), consists of a small hand-squeezed rubber bellows fitted down the sloping silage to try to rescue his brother, his father with check valves. One or more specified strokes of the watched him drop unconscious almost immediately. Even if bellows are required, depending on the concentration of the rescue could have been completed within minutes, it is very gas (the weaker the mix the more strokes to be counted). unlikely that either Eldon or Edward could have been revived). Research showed that the Drager bellows type was easier to use than the piston type and more suitable for the wide ranges Even small periodic dosages of N02 (such as from working of temperature and humidity encountered in and around farm each day in a poorly-ventilated feed room at the bottom of the silos. Consult the Drager chemical tube specifications and take silo chute) has been blamed for a host of chronic respiratory special care when interpreting the readings at temperatures problems, including shortness of breath, coughing and fluid in below freezing. the lungs. These symptoms can also result from a single non-lethal exposure and may be first noticed several weeks afterwards. This delayed effect has sometimes made an accurate diagnosis difficult. DETECTING SILO GASES During the danger period after filling the silo, use the following silo gas indicators: • Acrid bleach-like odor or a brownish to yellowish haze at the silage surface or on the feed room floor can indicate nitrogen dioxide. Sometimes an unnatural bright-yellow to orange coloration in the silage is another indicator. • Unnatural breathing, or coughing of livestock and people, may indicate either N0 2 or C02, or both. • Dead flies, cats or mice on the feed room floor, or dead birds in the silo, may indicate silo gases. Animals on the floor will be exposed to heavier gas concentrations than a standing person. In addition, chemical detectors are available for many hazardous gases, including C0 2, combined NO and N02 (NOX), Figure 3. Drager gas tester consisting of bellows pump, and N02 alone. The simplest of these is a paper tape that attached chemical tube and extension hose for changes color when exposed to N02 in silos and feed rooms, remote sampling. but it doesn't indicate how much gas is present. The tape is therefore not recommended. A practical difficulty is that all of these chemical tube detectors are calibrated with the glass tubes plugged directly into their air CHEMICAL TUBE DETECTORS, on the other hand, can be pumps. This means that the operator himself must enter the calibrated and should be considered for use by trained silo or other danger area, which is hazardous unless he is technicians and rescue teams (firemen, etc.). This type of wearing a remote air supply system. Use of the tube detector detector consists of a sealed glass tube containing a specific will give the best indication that it is safe for others to follow chemical reagent that changes color progressively along its without the protection of a remote air supply system. For length when the gas in question is drawn through the tube. practical purposes, an extension tube up to 5.5 m (18 ft) long Each tube is activated by snapping off both ends of the glass (provided by the manufacturer) is probably accurate enough and plugging it into a small hand-operated air pump. Operating when reading near the threshold limit values. At least two instructions specify the number of pump strokes required to chemical tubes for each gas (C02 and NOX) should be used to draw a specified air volume through the sampling tube. The check a silo. In many cases the extension tube is not nearly gas concentration is read either directly or by comparing the long enough to reach from the safety of the outside silo ladder length of tube that has changed color to tables or charts down to the sampling point inside the silo. reading in parts per million (ppm), by volume. THRESHOLD LIMIT VALUES (TLV) are the upper safety limits of hazardous gas concentrations. The American Conference of Several approved brands of tube detectors (MSA, Kitagawa, Government and Industrial Hygienists (1980) has published Drager, and Gastec) are available at safety supply stores. One two values: the TLV-TWA (time weighted average) value is the type of air pump consists of a piston and cylinder somewhat upper safety limit for workers repeatedly exposed for the like an oversized hypodermic syringe. One pull of the handle typical 8-hour workday; the TLV STEL (short-term exposure draws a precise quantity of the air in question (typically 100 limit) is the upper safety limit for four daily exposures of up to mL) through the chemical tube. 15 minutes, separated by 1-hour periods of no exposure. The This simple adaptation improved remarkably the penetration of latest published values for silo gases are: the air-blast deep into the silo headspace. The makeshift TLV-TWA TLV-STEL arrangement shown in Figure 2 was experimentally effective, (ppm) (%) (ppm) (%) but there is too much chance that in a real gas -hazard situation the tube could be dislodged by air and vibration. This Carbon dioxide (C0 2) 5000 0.5 15 000 1.5 could leave someone in the silo without a continuing air Nitric oxide (NO) 25 35 supply. Therefore the tube should be tied securely in place.__ Nitrogen dioxide (N0 2) 3 5 Oxides of nitrogen 'Spring Flex' tubing, by Flexhaust Co., 11 Chestnut St., (NOX) 3* 5*____ Amesbury, Mass., U.S.A. Available from Indus trial Rubber * Based on the most dangerous possibility that all the NOX can products, 90 Commander Blvd., Agincourt, Ont. M1S 3H7, convert to N02 and ForestTube Inc., 3555 boul. Cremazie E., Montreal, Que., H1Z 2S3. VENTILATING THE SILO AND FEED ROOM PORTABLE EXHAUSTER FANS were tried in controlled experiments with C02 in full-size farm silos. Two sizes of electric blowers were tested, each being connected to 15 m (50 ft) of clothes-drier hose. The larger blower was rated at 215 L/s when connected to the collapsible tubing. Once in place and operating, it reduced the C02 concentration in the silo headspace to that of normal air (around 3000 ppm) in 15 to 20 minutes. However, it was quite difficult to place the tubing at the far side of the silo while standing safely in the ladder cage outside the roof. Probably few farmers would buy and routinely use such special-purpose equipment. THE FORAGE BLOWER can move more air than any other easily-portable system, and it has the important advantage of already being in place at the end of silo filling. Air-moving capacities of various forage blowers running 'empty' at rated tractor speed were from 800 to 1000 L/s (1700-2100 cfm); this is about five times the capacity of the larger portable exhauster that was tested! After the initial 5-8 days of most rapid gas production, the forage blower is the most practical way to remove silo gases. A forage blower, equipped at the top of the silo with the side-fill deflector-type of silage spreader (Badger, Lancaster Multi-flo, etc.), is effective as long as the silage level is not more than 5 m (16 ft) below the distributor hood. At greater headspace depths, however, the splitter vanes appear to break up the airflow and prevent the air stream from penetrating deep enough to properly mix and displace the bad air deep inside the silo. With the various types of rotating center-fill silage dis tributors (Even-flo, Butler, etc.) some of the air blast is lost from the open underside of the long arched gooseneck, and the rotating distributor baffle-plate further deflects the remaining air-blast toward the silo wall. With a center-fill spreader attached, the forage blower gives rather poor ventilation, especially where the headspace from distributor to silage is greater than 5 m. To better direct the air-blast downward and to prevent 1 forage blower interference by the silage distributor (either type), a 5 m (16 ft) 2 fixed filler pipe, 230 mm (9 in.) length of 200 mm (8 in.) wire-wound flexible exhaust ducting * 3 200 mm (8 in.) Spring Flex wire-wound tubing was stuffed into the throat of the blower pipe (Figure 4). 4 air blast penetrates to bottom of headspace 5 mixed and diluted silo gas escapes through open roof hatch Figure 4. Silo ventilation by forage blower and flexible drop-tube stuffed into throat of silo filler pipe Really, a better method of attachment is required. Figure 5 opinion, we also found that the forage blower was more shows a suggested adaptor for the rotary center fill type effective as a silo ventilator with all the CHUTE DOORS distributors. At this time, we are recommending to silo CLOSED and the ROOF PANEL OPEN. equipment manufacturers that they develop and market these important safety devices. This procedure also avoids the dangerous possibility of the silo gas simply moving from the silo down into the feed room and Another important fact was discovered. Contrary to popular connecting stable. 1 attachment fitting and rectangular-to-round 3 external crank and cable pulls valve to transition piece; bolts to throat of gooseneck, 'bypass' position for ventilating the silo bolt heads smooth and flush inside throat 4 200 mm (8 in.) 'Spring Flex' wire-wound 2 diverter flap-valve spring-loaded to 'open' ventilaon tubing, gear clamp to transition position piece 1 Figure 5. Proposed gooseneck attachment for diverting the ventilation down into the silo headspace (gooseneck design by Lancaster Level-Flo, Inc., Lancaster, Pennsylvania 17602, USA). In an emergency, black plastic drainage tubing 200 mm (8 in.) This prevents effective natural ventilation that could be diameter, without perforations, could be substituted for the accomplished by opening an outside feed room door. more durable and lightweight wire-wound ventilation ducting. A simple and inexpensive solution is to move one of the barn exhaust fans (the one that runs most) to the feed room. This Table 1 gives calculated ventilation times for various sizes of will exhaust the barn air through the feed room, instead of the silo headspace, assuming ventilation with a forage blower at reverse. To make sure that the heavier-than-air silo gases are 800 L/s (full rated tractor pto speed of 540 rpm) and an initial effectively removed, build a box duct over the inside of the fan gas concentration of 10% C02. In headspaces of 6 m (20 ft) and extending down to about 150 mm (6 in.) from the feed and deeper, this table is valid only with the drop pipe room floor. The opening areas of the duct cross-section and attachment in place. Also, this table is not applicable to the the inlet at the floor should each be at least twice that of the period of most rapid gas production, for 5-8 days after filling - fan opening. The feed room should be insulated to prevent during this extreme danger period, even the forage blower is condensation on the walls and ceiling. too small to assure enough gas dilution for safety. A further advantage of this arrangement is that in winter the TABLE 1 MINIMUM TIME TO VENTILATE TOWER SILO feed room is heated at no cost by warm air drawn from the HEADSPACES livestock barn. It will be necessary to use some closure such Silo Ventilation time* (minutes) for headspace as a silage funnel attachment to close off the bottom of the silo diameter _____________depths of________________ chute. This is to ensure that the fan will draw air from the stable, not from the silo. The silage funnel should be tied off 3m 4.5 m 6m 7.5 m 9m with a plastic bag (or other suitable closure) except when the m (ft) (10 ft) (15 ft) (20 ft) (25 ft) (30 ft) silo unloader is operated. 3.6 (12) 3 4 5 7 8 4.8 (16) 5 7 9 11 13 6.0 (20) 7 10 14 17 21 7.2 (24) 10 14 20 25 29 REFERENCES * based on C-Ci = e –KQt/V 1. Airborne Contaminants Committee. 1980. TLV's, Co-Ci threshhold limit values for chemical substances and where C = C02 gas concentration at time t (assumed 0.015, the physical agents in the workroom environment, with TLV-STEL) intended changes for 1980. Amer. Conf. of Govt. Industrial Ci = inlet C02 concentration (assumed 0.0003, as in fresh Hygienists, PO. Box 1937, Cincinnati, OH 45201, U.S.A. air) 2. Wells, D. 1980. Respiratory protection for agricultural Co = original C02 concentration (assumed 0.10 in the tower silos and manure pits. Farm Safety Assoc. Inc., 340 headspace) Woodlawn Rd. W., Guelph, Ont. N1H 7K6. K = mixing factor (assumed 1.0) Q = ventilation rate (assumed 48 m³/min) 3. Sabourin, H.M., W.S. Reid, J.E. Turnbull and M. Ihnat. t = ventilation time, min 1982. Silo gas production, detection, ventilation and related safety procedurs. Can. Soc. of Agric. Eng. paper V = headpsace volume, m³ no. 82-207, presented at ann. conf., Vancouver, B.C. e = 2.718 Contribution no. I-421, from Eng. and Stat. Res. Center, Research Br., Agriculture Canada, Ottawa K1A OC6. THE SILO UNLOADER (once installed and operating) is an effective silo ventilator, but it provides no ventilation (and 4. Turnbull, J.E. 1984. Silo gas - what can be done? Proc., hence no protection) before it is lowered to the leveled silage Int. Silo Safety Conf., Kitchener, Ont. Nov. 28. surface, adjusted and started up. This start-up time is, Contribution no. I-660, from Eng. and Stat. Res. Center, unfortunately, the time of greatest risk from silo gas. Research Br., Agriculture Canada, Ottawa K1A OC6. 5. Meiering, A.G., M.G. Courtin, S.F Spoelstra, G. Pahlow, FEED ROOM VENTILATION is important as well. There is a H. Honig, R.E. Subden and E. Zimmer. 1988. real danger that silo gas can fill up to the level of the open Fermentation kinetics and toxic gas production of silages. chute doors and spill down the silo chute. This is of little Trans. of ASAE. Vol. 31. consequence if the silo stands alone outside and is connected to the feed room with only a feed conveyer. In most cases, however, the silo chute connects directly through the roof of an attached feed room, and the feed room connects in turn with the barn. Exhaust ventilation fans in the barn can easily draw silo gases through the crack under the feed room door, endangering livestock as well as people. The problem is potentially worse where the feed room floor is below outside ground level (a common situation with bank barns).