standards are considered similar to n95 in the us: japanese ds2/rs2 (jmhlw-notification 214, 2018): eu-like grades with two-letter prefix – first letter d/r stands for disposable or replaceable; second letter s/l stands for dry (nacl) or oily (dop oil) particles. japanese ds2 respirators are made by companies such as hogy medical, koken, shigematsu, toyo safety, trusco, vilene and yamamoto safety. mexican n95 (nom-116-2009): same grades as in niosh. brazilian pff2 (abnt/nbr 13698:2011): eu-like grades. disinfection and reuse hard filtering facepiece respirator masks are generally designed to be disposable, for 8 hours of continuous or intermittent use. one laboratory found that there was a decrease in fit quality after five consecutive donnings. once they are physically too clogged to breathe through, they must be replaced. hard filtering facepiece respirator masks are sometimes reused, especially during pandemics, when there are shortages. infectious particles could survive on the masks for up to 24 hours after the end of use, according to studies using models of sars-cov-2; in the covid-19 pandemic, the us cdc recommended that if masks run short, each health care worker should be issued with five masks, one to be used per day, such that each mask spends at least five days stored in a paper bag between each use. if there are not enough masks to do this, they recommend sterilizing the masks between uses. some hospitals have been stockpiling used masks as a precaution. the us cdc issued guidelines on stretching n95 supplies, recommending extended use over re-use. they highlighted the risk of infection from touching the contaminated outer surface of the mask, which even professionals frequently unintentionally do, and recommended washing hands every time before touching the mask. to reduce mask surface contamination, they recommended face shields, and asking patients to wear masks too ("source masking"). apart from time, other methods of disinfection have been tested. physical damage to the masks has been observed when microwaving them, microwaving them in a steam bag, letting them sit in moist heat, and hitting them with excessively high doses of ultraviolet germicidal irradiation (uvgi). chlorine-based methods, such as chlorine bleach, may cause residual smell, offgassing of chlorine when the mask becomes moist, and in one study, physical breakdown of the nosepads, causing increased leakage. fit and comfort do not seem to be harmed by uvgi, moist heat incubation, and microwave-generated steam. some methods may not visibly damage the mask, but they ruin the mask's ability to filter. this has been seen in attempts to sterilize by soaking in soap and water, heating dry to 160 °c (320 °f), and treating with 70% isopropyl alcohol, and hydrogen peroxide gas plasma (made under a vacuum with radio waves). the static electrical charge on the microfibers (which attracts or repels particles passing through the mask, making them more likely to move sideways and hit and stick to a fiber; see electret) is destroyed by some cleaning methods. uvgi (ultraviolet light), boiling water vapour, and dry oven heating do not seem to reduce the filter efficiency, and these methods successfully decontaminate masks. uvgi (an ultraviolet method), ethylene oxide, dry oven heating and vaporized hydrogen peroxide are currently the most-favoured methods in use in hospitals, but none have been properly tested. where enough masks are available, cycling them and reusing a mask only after letting it sit unused for five days is preferred. it has been shown that masks can also be sterilized by ionizing radiation. gamma radiation and high energy electrons penetrate deeply into the material and can be used to sterilize large batches of masks within a short time period. the masks can be sterilized up to two times but have to be recharged after every sterilization as the surface charge is lost upon radiation. a recent development is a composite fabric that can deactivate both biological and chemical threats