Is FAS safer than Sodium Hydrosulfite?
Direct Answer
Direct Answer It is safer in all three respects, handling, storage and transport. But safer is relative, and it does not mean harmless.
Why it is safer
- Behaviour with water: sodium hydrosulfite decomposes exothermically on contact with a small amount of water, can self-ignite and releases sulphur dioxide. formamidinesulfinic acid (FAS) dissolves and decomposes slowly and controllably, with no risk of flash ignition
- Storage and transport window: hydrosulfite normally needs low temperature, sealed moisture-proof packaging and cannot be loaded in rain. FAS needs only normal dry conditions, leaving much more margin in warehousing and freight
- Exposure at the point of use: the solution is stable and does not release irritant gas abruptly, so worker exposure and emergency pressure are lower
- Odour: essentially odourless, whereas hydrosulfite releases sulphur dioxide in hot alkali with a sharp smell
Hazard classification (per our SDS)
| Classification | Category |
|---|---|
| Acute oral toxicity | Category 4 |
| Acute inhalation toxicity | Category 4 |
| Skin irritation | Category 2 |
| Serious eye damage | Category 1 |
| Specific target organ toxicity, single exposure | Category 3 |
| Specific target organ toxicity, repeated exposure | Category 2 |
| Self-reactive substances and mixtures | Type G |
Principal hazard statements
- H252 Self-heating in large quantities; may catch fire
- H302 Harmful if swallowed
- H315 Causes skin irritation
- H318 Causes serious eye damage
- H332 Harmful if inhaled
- H335 May cause respiratory irritation
- H373 May cause damage to organs through prolonged or repeated exposure
Transport classification
UN 3341, Class 4.2 self-heating substance, packing group II, not classified as a marine pollutant.
Why it still cannot be called harmless
The classification includes inhalation toxicity and target organ toxicity, so operators still need a dust mask, goggles and gloves, dust inhalation must be avoided, and the workplace must be ventilated.
Bottom line
Safer than hydrosulfite in handling, storage and transport, but the safety is relative: the seven classifications and seven hazard statements in the SDS still have to be put into practice.
Sources
- 我司产品 SDS 与 TDS（危害分类、运输分类、热分解温度、溶解度等物性数据）
- US5958184A, Process for producing thiourea dioxide（还原当量质量比、碱中水解式、木浆与脱墨浆等当量漂白实施例），https://patents.google.com/patent/US5958184A/en
- 我司产品安全数据表《Material Safety Data Sheet — THIOUREA DIOXIDE》（MSDS，签发日期 2023-03-03）
- 我司产品技术数据表《THIOUREA DIOXIDE Technical Data Sheet》（TDO-TDS，签发日期 2024-05-08）
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