For more than two decades, science has recognized that building fires have become hotter, faster-spreading and more toxic. One engineer blames it on the world’s “addiction to polymers,” a reference to synthetic materials that are everywhere—from the exterior wall systems that wrap modern towers to the furniture, carpets and even decorative features. As the fire safety publication NFPA Journal described in a headline, often what “Looks Nice, Burns Hot.”

The danger to people in burning buildings is greater. What was in the 1970s an average timeframe of 17 minutes in which occupants of a home had to escape after a smoke alarm activated, according to Underwriters Laboratories (UL), has shrunk to just two or three minutes.

At the same time, fire-resistant buildings and improved fire-suppression techniques have reduced the incidence of fire. But advances have been “somewhat offset by increases in the number and value of buildings,” reports the Insurance Information Institute.

2017年6月14日,讨论建筑fires changed. That day, a fast-moving fire climbed the sides of a 24-story public housing tower in London, killing 72 people. The repercussions of the Grenfell Tower disaster, along with other recent fires involving exterior walls with combustible materials, everywhere from Australia to Dubai, are still being felt. By May of this year, England’s government had made $250 million in funding available to private owners of apartment buildings to replace panel assemblies of the Grenfell Tower type. A state in Australia has also made financing available to replace panel assemblies.

The reverberations go further. Although U.S. codes are stricter about the use of metal composite material exterior panels than those used in England, and there have been no Grenfell-type tragedies in the U.S., a committee of the International Building Code did take steps to tighten the code to require that assemblies using such panels be fire-tested even in buildings with sprinklers. Beyond that, a new round of discussion started over whether the most frequently used test to gauge the reaction of Grenfell Tower-type exterior wall systems and all metal composite material exterior walls is the best choice.

消防工程师道格拉斯·H·埃文斯（Douglas H. Evans）指出：“这是该行业的辩论。”“如果我们考虑了已经使用了80年的标准时间温度曲线，并将其与如今的时间温度曲线进行更合理的[评估]进行比较，那么[问题是]是否需要任何更改。透明

一般而言，防火虽然不一定在美国，但已经崩溃了，这一想法来自美国消防专业知识的最高水平。国家消防协会（NFPA）主席吉姆·保利（Jim Pauley）在博客文章中询问格伦费尔（Grenfell）和其他最近的火灾灾难，问：“我们在哪里误入歧途？”他举例说，使用过时的代码和标准，安全要求的省钱减少，忽略了代码中的参考标准，并且普遍缺乏执法，教育和意识。其他s have stated that when it comes to building exterior walls, owners and designers are confused about the different composite systems and that NFPA’s important NFPA 285: Standard Fire Test Method for Evaluation of Fire Propagation Characteristics of Exterior Non-Load-Bearing Wall Assemblies Containing Combustible Components, may not be followed.

大规模火灾测试本身的可能缺点也在不同的时间出现。尽管该方法仍然是学习点火开关，火焰传播和建筑外墙组件的其他特征的唯一可能方法，但测试“非常昂贵，破坏性，并且由于许多实际的限制，通常是不可能的，”来自澳大利亚和中国的建模，在《杂志》杂志上的一篇文章中。根据国家标准技术研究所的火灾模型简报，全面测试“有时不可能为所需条件执行”。

The fire test discussion centers around three key building exterior wall fire safety tests: NFPA’s 285, insurer FM Global’s ANSI/FM 4880 PPT and England’s BS 8414. They differ substantially in the heat source used and distance from the source, heat release rate and failure criteria (see p. 26).

例如，NFPA 285用作热源两种丙烷燃烧器，ANSI/FM 4880依赖于一个丙烷燃烧器，而BS 8414在墙壁​​底部使用木材床。

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Gold Standard

The widely respected test published by NFPA, which oversees 300 codes and standards created by thousands of volunteers, has been the gold standard. The 30-minute fire test centers on a two-story, 17.5-ft-high mock-up, with a window in the middle of the lower floor. The scenario involves a flashover fire in the lower story that sends flames out the window and onto the exterior cladding.

The propane burners used—one in the lower-level room and another located under the window opening—provide a flow of heat to the exterior assembly being tested. The flow is gradually increased over the 30-minute test, with the highest heat reserved for the final five minutes. During the test, the temperature is also monitored inside the insulation and air cavities as well on the front of the facade, with thermocouples placed at various points across and inside wall assembly.

To pass, temperatures 10 ft above the window and 5 ft across from its center cannot exceed 1,000° F, while the insulation underneath the panels can’t exceed 750° F. The temperature of the interior wall in the second story room can’t exceed 500° F at a depth of 1 in. from the surface.

NFPA建筑防火和消防系统主管罗伯特·所罗门（Robert Solomon）说，NFPA 285仍然是“非常具有挑战性的测试”。

BS 8414在英格兰使用的测试，比NFPA 285的组件受到更多的能量和更高的热量。它涉及在角落情况下排列的26英尺高的主壁和机翼。主墙宽8英尺，而机翼壁必须至少为4英尺。

BS 8414的热源是木床。注意力集中在主墙开口上方的3.3英尺上。如果第二级的热电偶温度在点火点后15分钟至少半分钟，则面板会失败。

FM批准是与FM Global（保险公司）隶属于FM Global的第三方认证和测试服务，从1880年代开始生活，作为工厂共同实验室。它的网站表示，它已经制定了200多种批准标准。该部门的批准标准是室内饰面材料的1级火灾额定等级，4880年，可追溯至2015年10月，也获得了美国国家标准学院（ANSI）的认可。火灾测试依赖于平行面板测试，其两个16英尺的面板约为3英尺，底部有一个3.5英尺的砂燃烧器。15分钟的测试的丙烷热释放速率为360 kW。整个测试设置都放在热量计罩下，以测量释放速率和烟雾。

FM Global notes in a white paper that “fire incidents” around the world warrant an “international effort to reinvestigate and scrutinize building codes and the corresponding standard testing methods for such external wall assemblies.”

In carrying out the ANSI/FM Global 4880 test, the laboratory staff directs 100 kW per square meter of energy onto a panel assembly, more than twice that of NFPA 285.

FM Global新利18备用最近的一项研究检查了七个不同的外部面板组件，该组件用铝核心进行了研究。这些包括不同类型的此类面板和面板之间的两种不同类型的绝缘材料。七个组件中有六个以前已经通过了NFPA285。其中两个小组组件通过了NFPA测试“果断失败” FM Global的平行面板测试，其中四分钟内火焰射击了25英尺，这时测试结束了。根据FM Global研究，两者都使用了“具有相对较厚的铝面的可燃热核[铝制核心面板]”。新利18备用另外两个通过NFPA 285的小组组件足够好，没有对其使用的高度限制，仅通过了FM Global的4880，用于50英尺以下。

“The fire test may be large-scale in nature, but it won’t capture the vertical fire spread behavior of the wall system if the heat flux exposure is too low,” the study notes.

当2010年对绝缘层以及空气和水障碍的需求增加时，NFPA 285更加重要。随着当时对国际建筑法规的更新，随着其他可燃组件包含在更新中，它的相关性越来越大。通过NFPA 285测试对于建筑覆层材料的制造商，例如杜邦和欧文斯 - 折叠至关重要。Owens-Corning在其营销材料中，涵盖了涵盖各种砖石饰面外部饰面的“外壳解决方案”通过测试的事实。其产品的在线手册包括火灾测试的照片。

现在，FM Global表示，现在是时候改变测试的时间了，认为它们可能根本不够热，也不足够强烈，无法真正捕捉到当今火灾的凶猛。保险公司还在外墙组装的一条小册子中指出，“建筑物和消防法规通常是共识创建的最低标准，主要集中于生命安全”，并且不必“提供最佳的财产损失”建议。

几年前，当消防员开始报道说，当他们独立的呼吸器上的镜头在建筑物和其他建筑物中战斗时，人们对现代大火变化的关注被驱赶回家。

美国国家标准技术研究所（National Standitds of Stradions of Technology）的消防研究部代理主任纳尔逊·布莱纳（Nelson Bryner）帮助领导了提高用于证明消防员呼吸设备的测试中的热量水平的努力，并在NFPA监督的代码中设定了新标准。布莱纳说：“我们重新设计了测试，并大大升高了温度。”

Oxygen Bomb Method

As modern fires grew hotter and more dangerous, different players in the testing business began pushing rival methods. A British research team argued the small-scale oxygen bomb method of testing has the potential to be both more effective and more cost effective compared to large-scale wall assemblies.

However, Abhishek Chhabra, market development manager for Thomas Bell-Wright International Consultants in Dubai, contends the oxygen bomb test on its own is not sufficient. Chhabra advocates for a two-tiered testing process, with oxygen bomb, calorific-style testing of specific materials followed by further tests using a larger-scale mock-up.

Chhabra suggests the first step is to gain an understanding of how the material in question reacts to fire. But just simply knowing how individual materials react to fire is one thing. A larger-scale mock-up is needed to understand how differing materials with differing fire properties perform when combined on the facade of a tower or building.

“人们在设计系统时无法理解的是，邻接会发挥作用。如果[组件一个]确实着火，那将点燃材料两，”恰布拉说，以身作则。

在实验室中对特定材料进行小规模测试的角色，总部位于英国FM Global的国际消防安全法规和标准的高级顾问Tom Roche回答。但是，使用更大的实际材料模型反映了它们如何在实际的塔楼或建筑物中使用的实际材料，因此没有替代火灾安全测试。

“Yes, you can infer things” from small-scale material testing, “but if you really want to know, large scale testing is what you need to do,” says Roche.

To be sure, a nonprofit code-writing organization such as NFPA brings together code officials and the industry stakeholders when revising its codes and standards. NFPA updates then make their way into other safety and building codes. The organization describes its educational mission as eliminating “death, injury, property and economic loss from fire, electrical and other hazards.” And it is, on balance, successful.

The question is whether the ANSI/FM approval standard is a case of risk-control overkill, especially for the way it could affect construction costs.

NFPA has updated and published research on combustible exterior wall assemblies in 2014 and last year. NFPA’s Solomon says FM Global had developed a “nice test,” but that it is focused on a much different scenario. FM Global’s parallel panel test is based on a dumpster or car fire spreading to the building, while NFPA’s test is based on a fire starting inside and flashing over onto the facade.

Solomon谈到FM Global测试时说：“这是一个更高的能量水平。”“我不会在80层建筑物的四楼外面有15立方英尺的垃圾箱。”他说，这种方法“不会采取任何措施来增强测试”。