For understanding red phosphorus fire retardants,The environmental impact of red phosphorus fire retardants


When chemical substances are used, there is always some kind of risk or hazardous properties. It is important to evaluate the quantity and period of exposure to a chemical substance as well as the degree of danger or harm inherent in the chemical substance itself, otherwise there is a risk of other dangers.
Red phosphorus itself must be handled as a Category II hazardous material under the Fire Service Act, but it is also possible to make it a non-hazardous material by converting it to a masterbatch. Moreover, the toxicity is low, and the risk to human health from any toxicity can be ignored.

There are no regulations prohibiting or restricting the use of red phosphorus fire retardants in Japan or any other country.

Red phosphorus is an environmentally-friendly fire retardant substance, and the quantity of decomposition products emitted from red phosphorus is infinitesimal, so that there is no environmental impact under normal usage conditions.


1. The regulatory status and toxicity of red phosphorus

The regulatory status and toxicity of red phosphorus

Red phosphorus is registered in the database of the Chemical Abstracts Service (“CAS” ? the information division of the American Chemical Society) as “phosphorus,” under the same number as the highly toxic yellow phosphorus. If you have investigated using the CAS registration number, check whether the item corresponds to “red phosphorus.”

1.1 Japanese statutory regulations

Red phosphorus is designated as a “combustible solid” (a solid that either ignites easily or which can easily catch fire at low temperatures), one of the Category II hazardous substances in the Fire Service Act.
(Specified quantity: 100kg)

1.2 Foreign statutory regulations

Red phosphorus is exempt from regulations governing harmful substances under RoHS (the EU’s Restriction of Hazardous Substances Directive), WEEE (the EU’s Waste Electrical and Electronic Equipment Directive) and ELV (the EU’s End of Life Vehicles Directive).

1.3 Other regulations

Green procurement
Red phosphorus is not listed in either Level A or Level B of the list of chemical substances that should be disclosed for products and components for electrical or electronic devices.

1.4 Assessment

German Federal Environment Agency (UBA)
Research report 204 08 542(old), 297 44 542(new)
(Microencapsulated) Red phosphorus:No environmental problems with use as a fire retardant

1.5 Acute toxicity

The LD50 level when administered to rats orally is 15,000 mg/kg or more, making red phosphorus practically harmless. The LD50 level for table salt administered orally to rats is 3,000 mg/kg.

1.6 Threshold limit value

Neither a TWA (Time Weighted Average) or a STEL/C (short term exposure limit and ceiling) has been established for red phosphorus.
Japan Society for Occupational Health (2006-2007)
No threshold limit value established.
Red phosphorus is classified as “other organic or inorganic dust”, for which the threshold limit values are 2mg/m3 for inhalant dust and 8mg/m3 for total dust.

1.7 Carcinogenicity

No reports of carcinogenicity in ACGIH (2006), Japan Society for Occupational Health (2006-2007), IARC MONOGRAPHS VOL.1 to 88(2006), or 67/548EEC Annex I (29ATPS)


ACGIH stands for the American Conference of Governmental Industrial Hygienists, a US organization of experts in industrial health and safety Every year, ACGIH publishes information in relation to chemical substances, physical effects and biomonitoring, for managerial and technical fields in relation to the health of the workplace and the environment. This information includes rankings of the carcinogenicity of chemical substances and recommended values for the tolerable concentrations in workplaces (the ‘TLV’ or Threshold Limit Value).


2. Toxicity of decomposition products

Red phosphorus fire retardants decompose extremely slowly, producing phosphine and oxacids of phosphorus. Even taking into account the impact of these decomposition products, red phosphorus fire retardants have no environmental impact.

2.1 TLVs for decomposition products

  Phosphine Phosphoric acid
(an example of an oxacid of phosphorus)
Chlorine Formaldehyde
CAS registration number 7803-51-2 7664-38-2 7782-50-5 50-00-0
TWA 0.3ppm 1mg/? 0.5ppm
STEL/C 1ppm 3mg/? 1ppm C 0.3ppm
Japan Society for Occupational Health
Maximum TLV 1mg/? Maximum TLV
  Maximum TLV

2.2 Work environment during processing

Phosphine gas may build up within the container while the product is being stored, so care is required not to breathe in the gas inside the container.
Only a miniscule amount of phosphine is released when compound resins are molded or processed using red phosphorus fire retardants. Normally workplaces are ventilated constantly, with local air exhausters installed at the necessary locations. In such circumstances, the concentration will not reach the threshold limit value for a work environment.
In our factory for manufacturing red phosphorus fire retardant masterbatches, the concentration drops rapidly as the distance from the area around the exhaust of the extrusion die increases, so that when setting 15 cm away from the exhaust of the die the concentration is less than 0.05 ppm, well below the threshold limit value.

2.3 The environment when red phosphorus fire retardants are used

Red phosphorus fire retardants are safe in daily life as well, given that the amount of phosphine emitted from products containing red phosphorus fire retardants is miniscule, and well below the threshold limit value for the work environment. Moreover, phosphine oxidizes easily, ultimately becoming either an inorganic phosphate or an oxacid of phosphorus.
The amount of oxacids of phosphorus released from products containing red phosphorus fire retardants is also miniscule, and is not at a level that has an effect on human health.

2.4 Noxious gases during fires

As for the toxicity of the combustion gases during a fire, the toxicity due to phosphine has been shown to be relatively small, with a higher impact resulting from the noxious gases emitted from the resin itself (such as CO, HCN, and HCI).
There is no need to consider the toxicity due to phosphine during fires.

2.5 Environmental impacts due to disposal

In water, products containing red phosphorus fire retardants release miniscule amounts of oxacids of phosphorus, such as hypophosphorus acid, phosphorus acid, and phosphoric acid, eventually converting into either phosphoric acid or one of its salts. Even if it ends up in landfill, it will not reach a concentration that will affect aquatic organisms, and will be absorbed by the natural environment, becoming a source of nutrients for the common plankton or becoming immobilized by forming inorganic substances in the soil or water-insoluble salts (such as salts of calcium and magnesium). A significant portion of the sources of phosphorus burden on the aquatic environment consist of natural sources, fertilizer, pesticides, livestock wastewater, and domestic wastewater. Given the low usage rate and the low level of solubility in water, it would be ridiculous to view eutrophication due to red phosphorus fire retardants as a problem. In relation to eutrophication, efforts are underway throughout society, focusing on wastewater.


3. Further information

Materials relating to the phosphorus committee of the Flame Retardant Chemicals Association of Japan

1)‘Position Paper on Eutrophication due to Red Phosphorus Fire Retardants’ (2006.07.01)
2)‘Test Report on Phosphine Emissions from Red Phosphorus’ (2006.01.18)
3)‘Phosphine Emissions from Red Phosphorus Fire Retardants’ (2005.09.01)
4)‘Overview of the Relative Toxicity of Red Phosphorus Fire Retardants’ (2004.12.03)
5)‘The Safety of Red Phosphorus Fire Retardants’ (2004.09.09)

Report of National Research Institute of Fire and Disaster
6)‘The toxicity of phosphine etc. when synthetic resins containing red phosphorus fire retardants are burned’ Report of National Research Institute of Fire and Disaster, Volume 80, pp 30-35 (1995)

Rin Kagaku Kogyo internal document
7)‘Environmental safety of red phosphorus fire retardants' (1999.03.15)

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