“Nowadays, the prevailing approach in pest management is the Integrated Pest Management (IPM) with emphasis on sustainability with the use of as less chemicals as possible. Through this approach, we invest most efforts in prevention, avoidance and monitoring so that control measures such as fumigation, would be applied only after all other alternatives were considered. Fumigants are among the most toxic pesticides in use; subject to injure people, animals and the commodity. The objective of this article is to provide basic information required before, during and after the performance of the fumigation. This article has the intention to provide information to people engaged in decision making regarding fumigation operations.”
Shlomo Navarro, Green Storage Ltd.
Hagit Navarro, Green Storage Ltd., firstname.lastname@example.org
Hazards of fumigants
There are numerous hazards of fumigants from several aspects. They can kill humans and animals or cause burns and damage human organs. They can cause fires and explosions. They can cause damage to commodity by their phyto-toxicity (i.e.: germination inhibition, burns), by discoloration or by causing corrosion to items. In some cases, they might exceed the legal residues level or produce off flavor and bad odor (Walter et al, 1999).
Therefore, a trained fumigator must be familiar with the fumigants registered in his country and know their limitations with regard to their characteristics, the legislation and the safety rules. After the decision to fumigate is taken, a fumigation plan must be conducted. Several aspects must be taken into consideration within this plan including risk assessment.
Before any fumigation is applied, fumigators must re-read the label. Labels are subject to change. The fumigator must make sure the fumigant can be used at the site, on the specific product and under the current climatic condition to ensure successful and safe application.
In some countries in Europe or Israel, phosphine fumigation is permitted in sites where there are neither people nor animals at a radius of 30 m and 200 m from sensitive areas such as hospitals, schools, retirement homes etc. Another significant consideration is whether the location for fumigation is suitable for safe aeration to release the fumigant after the exposure time is finished. The fumigator must examine products, items and people presence while fumigating and during exposure time. Additionally, when applying in-transit fumigation, the fumigator must ensure workers’ safety on ships and in ports.
Planning fumigation time
When planning fumigation, it is crucial to know when the commodity is planned for consumption or removal to another site. According to that, the fumigator should choose which fumigant to be used. Phosphine, Controlled Atmosphere (CA) or Modified Atmospheres (MA) require considerably long exposure times (more than 7 d) compared to Methyl Bromide (MB), Ethyl Formate (EF), Propylene Oxide (PPO) and Ethan Di-Nitrile (EDN) which require between 12-24 h treatments (Annis and Graver, 1990, Bond, 1984, Graver, 2004).
Gas tightness of the fumigation enclosure
The type of fumigation would be selected according to the structure in which the commodity is fumigated. The best option and most rare one is a rigid gas tight fumigation chamber. Gas tightness is determined by applying the half-life time pressure decay test (Navarro, 1998). It is a useful tool not only to ensure successful fumigation but also to determine the leakage degree of the fumigation structure with regard to people’s safety. Table 1 shows the recommended ranges of half-times for various applications. Half-life time pressure decay below those times, fumigation is not recommended. Half-life time pressure decay test is carried out by applying a positive or negative pressure for rigid structures but for flexible structures such as fumigation “bubbles” it is carried out only by applying negative pressure. To measure the pressure, fumigator must use a differential pressure gauge. Half-life time pressure decay test would not produce measurable levels under tarpaulin fumigation, whether the commodity is in bulk or in stack.
Table 1 - Provisional recommended ranges for variable pressure test carried out in structures destined for gaseous treatments to control storage insects.
Fumigator must monitor gas leaks with a personal safety gas detector device. Most common safety devices that are in the market today detect phosphine and MB at a range of 0-20 ppm. In most parts of the world. Threshold Limit Value (TLV) of phosphine in some counties is 0.1 ppm and for MB TLV is 1 ppm. Above these values, devices will alert the user (Bond, 1984). Today, there are also on-line monitoring devices which transmit a signal if concentration outside the fumigated structure exceeded its defined limits. In any fumigation, at least two people must be present, where one of them has to be a certified fumigator equipped with a personal gas detecting device.
Before fumigation, after all sealing has been done and before introducing the fumigant, fumigator must make sure there are life lines in case of an emergency. All fumigation structures must be properly posted with warning signs at eye height from all directions according to the local legislation.
Photo 1: The setup of the automatic gas monitoring warning system
Automatic gas monitoring warning system
A very modern automated system for people safety was recently presented by Centaur.ag and includes 2 levels of protection. The system contains multiple gas sensors reading low concentrations of phosphine, CO2 or Oxygen. The frequency of monitoring is set by the user. The first level of protection is the “safe to enter” barrier. The area manager allows workers to enter only when the green light is on. The second barrier is activated upon detection of unsafe conditions. The system then initiates a visual and sound alarm for people to exit the area and a warning red light by the door informs people not to entry. The system automatically starts aeration fans to clear the air. All actions are automatically recorded and reports are released. The current conditions and history are available in real time on the cloud for users with password from every computer or smartphone. One of the strongest points of this system is that is based on many sensors. Even if one sensor fails, the rest will still maintain safety. When a person’s safety is based only on his personal meter, the risk of failure can be lethal.
Personal Protective Equipment
All fumigant applicators (fumigators and operators) must be equipped with Personal Protective Equipment (PPE) according to fumigants’ labels. Different type of gloves is required for each fumigant. For example, since phosphine in its solid form sublimates to gas by reacting the moisture in the air (with water vapors) fumigation will require cloth gloves to avoid transfer of sweaty hands during summer (Annis and Graver, 1990). MB reacts with sulfur which is one of the components in rubber, therefore, rubber gloves for MB fumigation are not recommended (Graver, 2004).
Since the mode of action of all fumigants is by inhalation, most important component of PPE is a respiratory mask under the category of Respiratory Protective Equipment (RPE). There are various types of masks; for short term exposure and low concentrations (phosphine <1%, <MB 2%) usually from minutes to hours (Graver, 2004). The simplest form of mask is a disposable respirator or a reusable half-face respirator with a filter cartridge, usually a half-face mask covering the mouth and nose. Both will have an assigned protection factor of up to 10. They can be combined with goggles or obtained as a whole-face mask to protect the eyes as well. Usually, whole-face mask will have an assigned protection factor of up to 50 (Wikipedia, 2019).
For prolonged exposure times such as a rescue procedure during accident, remote breathing apparatus should be used. The simplest form is a flexible tube of about 25 mm internal diameter connected to the mask on the wearer’s face and opening in clean air. This should be used for distances of maximum 9 m long, distances greater than that will be too long for natural breathing. For applications requiring extended filter life, some respirators are equipped with hose adapter that allows two fitted filters to be belt mounted and oriented away from the source of contamination, further reducing breathing resistance and increasing filter life (Walter et al., 1999).
A more advanced form of mask is the powered RPE or Powered Air Purifying Respirator (PAPR). This respiratory protection device uses a fan to deliver filtered air into a variety of different headgear and facepiece options. A PAPR is battery-powered and comes in many configurations to make sure the wearer is completely comfortable, regardless of the workplace or environment (Wikipedia, 2017).
PAPR will enable protection from couple of hours to up to twelve hours with an assigned protection factor of up to 1,000. Some of the brands incorporate a downloadable data-logging function that automatically records usage and performance information - making record keeping much easier. Usually they will supply a continuous airflow of 160 l/min (Wikipedia, 2017).
When there is an immediate danger to life and health, the highest form of respiratory protection is the Self-Contained Breathing Apparatus (SCBA) and pressure demand supplied air will protect the wearer for 30-75 minutes with an assigned protection factor of up to 10,000. SCBA is equipped with cylindered air (Wikipedia, 2019b).
Whether it’s a half-mask, a whole-mask (non-powered respirators), powered RPE or SCBA it is most important that the mask would fit properly. Wearer must be shaved. Each time the mask is put on, a check must be carried out to ensure that the rubber face piece is giving a good seal on the face. This is done easily by pinching the hose of the respirator or sealing the opening of the cartridge. If it fits properly then the wearer will not be able to breath as the mask will collapse against the face.
There are various filter cartridges available today in the market which gives protection against dusts, sprays, organic and inorganic vapors. All of them supply protection for short exposure time and low concentrations. Each cartridge would be marked on which specific toxicant it protects from and the degree of protection (marked from 1-3, where 3 symbols greater protection). Each cartridge has a maximum shelf-life of 6 months after it is opened. After each fumigation procedure cartridge should be removed from the mask and kept in a tight container when not in use. The mask should be washed and left to dry. It is most important to manage a list of the time used with the filter with all types of the non- PAPR to ensure wearer safety (Walter et al., 1999). Table 2 shows the color and letters coding of filters indications for each group of substances or particles. These could also be found in the market as combination filters which have more than one color code and letter code. For phosphine, operator would use “B” grey filter, for MB, EF, EDN and PPO “AX” brown filter. Most labels will recommend using ABEK P3 which is more expensive and protects also against high concentration of particles (P3).
Table 2: Color and letter codes of filters indications for each group of substances or particles.
Aeration and release of fumigant residues
When fumigation is over, the release of the fumigant is an important procedure. This procedure involves, where possible, active aeration. Most grain silos are equipped with aeration system. Such aeration systems operate within a range of airflow 3 to 12 (m3/h)/tonne (Annis and Graver, 1990). It is important to ensure that such airflow is available and it can be used to remove the fumigant. With airflow in pressure system, during aeration, the exhaust system should convey the air directly to the atmosphere. In suction systems (airflow from top to bottom of the silo), gas contaminated air is conveyed to the bottom of the silo, Therefore, care should be taken to avoid presence of workers at air exhaust point, To avoid workers respiration of the fumigant contaminated air, warning signals that the fumigant is released to the atmosphere should be placed in visible sites (Annis and Graver, 1990). To ensure complete release of the fumigant, an intermittent aeration procedure should be applied. In this process, after an initial two hour aeration, several hours of pause will enable desorption of the gas that was sorbed (absorbed) by the commodity into the interstitial airspace of the grain bulk. Such procedure can be applied for phosphine with two cycles of intermittent aeration and for methyl bromide several more cycles would be necessary.
For facilities that are not equipped with aeration system, the solution is to turn the grain through the conveyor chains and elevators. This process causes in each passage the grain to shrink (and break), facts that are far less desirable than aeration for releasing the fumigant. In some cases for grain stored in silos without aeration systems, after fumigating with phosphine gas, a simple opening of the top silo hatch is considered as aeration. This method has its own disadvantages of spreading uncontrolled phosphine concentrations around the silo posing a risk to workers safety.
Following a fumigation under tarpaulin, the conventional method is to uncover the stack of grain and release the fumigant to the warehouse or enclosure where the commodity is stored. In such case extreme care should be taken by the fumigator to use appropriate RPE during the uncovering the tarpaulin. In addition, workers should be warned not to enter the premises where the fumigant is released. The fumigator should check the gas concentration using the personal gas detector to ensure that the concentrations are below the permissible limit for entering the premises.
When fumigating with solid phosphine (pills/tablets/blankets/plates), the fumigator must collect and deactivate the remaining phosphide dust. During deactivation, the fumigator must be protected with PPE which includes a mask, goggles (or whole-face mask), gloves, working shoes.
Fumigants are among the most toxicant products of all pesticides. One should act with care and attention while in any kind of operation with them. Most fumigants are odorless, colorless and cannot be detected unless using a specific measuring device.
Annis, P. C., & Graver, J. V. S. (1990). Suggested recommendations for the fumigation of grain in the ASEAN region
Bond, E. J., & Monro, H. A. U. (1984). Manual of fumigation for insect control (Vol. 54). Rome: FAO.
Graver, J. V. S. (2004). Guide to fumigation under gas-proof sheets. Food and Agriculture Organization of the United Nations.
Navarro S. (1998) Pressure tests for gaseous applications in sealed storages: Theory and practice. p. 385-390 (Vol. I) (In) Proc. 7th Int. wkg. Conf. Stored-Product Protection, (Eds. Zuxun, J., Quan, L., Yongsheng, L., Xianchang, T., and Lianghua, G.) 14-19 October Beijing China, Sichuan Publishing House of Science and Technology, Chengdu, Sichuan Province.
Walter, V. E., Gold, R. E., & Hamman, P. J. (1999). Structural and Commodity Fumigation. Texas Agricultural Extension Service, Texas A & M University System.
Wikipedia (2019a) https://en.wikipedia.org/wiki/Respirator_assigned_protection_factors. Last edited on 15 March 2019
Wikipedia (2017) https://en.wikipedia.org/wiki/Powered_air-purifying_respirator last edited on 7 April 2017
Wikipedia (2019b) https://en.wikipedia.org/wiki/Self-contained_breathing_apparatus last edited on 8 June 2019.