Every time we publish an article about Hempcrete, we get a lot of comments on social media - with a certain level of irony - about what would happen if the material caught fire. This is actually a legitimate question, as there is still a lot of confusion about the differences between marijuana and hemp, both of which come from the same plant species (Cannabis Sativa). But while marijuana has psychoactive effects due to tetrahydrocannabinol (THC), mainly present in the flowers of the plant, hemp-based building materials are produced from its stem, which contains small amounts of THC. To quickly answer the title question: no, the building won't be destroyed in the event of a fire. In fact, some tests have shown that these materials have excellent behavior against fire, dissipate flames, maintain structural integrity, and don't emit toxic smoke.
The use of hemp in civil construction is a fairly old practice and several studies have shown how beneficial this plant can be for the future of the industry. It is a material with a negative carbon footprint, meaning that it absorbs more carbon than it emits in its production and, at the end of its useful life, it can be returned to the environment, degrading naturally. In concrete mixers, hemp, powdered limestone and water are mixed to obtain a thick paste, which through chemical reactions petrifies and becomes a light but very resistant block. For wall construction, the mix can be laid out as non-structural blocks, sprayed, or poured into linear shapes, in the same way as mud walls. Hempcrete has excellent thermoacoustic properties, helps regulate indoor temperature and humidity, and is resistant to mold.
Unlike what you might imagine, hemp-based materials work very well when exposed to fire. In order to measure the characteristics of each material, tests are carried out following specific rules. In the United States, for example, ASTM E 84-19B test results for hemp concrete showed impressive performance, reaching top marks for "flame spread" and "smoke production" ratings.
In Australia, a fire test has been documented to simulate embers' attacks during wildfires, where there is a potential for fuel to accumulate at the base of the walls. This is a particularly worrying situation in Australia, where large forest fires routinely occur. No damage was observed on the 200 mm thick hemp concrete walls, which were exposed to a 600 mm high flame, burning directly against the wall for a period of 60 minutes.
Similar results were verified in this collection of experiments with hemp concrete, where it is observed that hemp concrete forms a barrier between the building structure and the fire. As a non-flammable material, hemp concrete doesn't allow flames to dissipate. According to the author of the study, "currently available data suggests that hemp concrete is suitable for applications where 60-minute fire resistance is required and that this can easily be increased to 90- or 120-minute fire resistance with changes in specification."
When it comes to forces of nature like fire, all necessary precautions are important to preserve lives and resources. That is why so many researchers are focusing on the subject, investigating the behavior of each material in a fire. In short, hemp-based materials provide adequate fire resistance so residents can evacuate in time, reducing the spread of the fire and the risk of inhalation of smoke as it burns locally. In other words, burning a wall of hempcrete will be very difficult and will not have any psychoactive effects. Jokes aside, hemp is still an extremely stigmatized material in many countries but it needs to be addressed seriously. Its many applications for various industries carry the enormous potential to replace other polluting materials that are harmful to the environment and may become the protagonists of a change in the civil construction industry.